     [file version.texi not included]

This file documents the recode command, which has the purpose of converting files between various character sets and surfaces.

Copyright (C) 1990, 93, 94, 96, 97, 98, 99, 00 Free Software Foundation, Inc.

Permission is granted to make and distribute verbatim copies of this manual provided the copyright notice and this permission notice are preserved on all copies.

Permission is granted to copy and distribute modified versions of this manual under the conditions for verbatim copying, provided that the entire resulting derived work is distributed under the terms of a permission notice identical to this one.

Permission is granted to copy and distribute translations of this manual into another language, under the above conditions for modified versions, except that this permission notice may be stated in a translation approved by the Foundation.

recode
******

This recoding library converts files between various coded character sets and surface encodings.  When this cannot be achieved exactly, it may get rid of the offending characters or fall back on approximations. The library recognises or produces more than 300 different character sets and is able to convert files between almost any pair.  Most RFC 1345 character sets, and all libiconv character sets, are supported. The recode program is a handy front-end to the library.

The current recode release is VERSION.

Quick Tutorial
**************

So, really, you just are in a hurry to use recode, and do not feel like studying this manual?  Even reading this paragraph slows you down? We might have a problem, as you will have to do some guess work, and might not become very proficient unless you have a very solid intuition....

Let me use here, as a quick tutorial, an actual reply of mine to a recode user, who writes:

     My situation is this---I occasionally get email with special characters in it.  Sometimes this mail is from a user using IBM software and sometimes it is a user using Mac software.  I myself am on a SPARC Solaris machine.

Your situation is similar to mine, except that I often receive email needing recoding, that is, much more than occasionally! The usual recodings I do are Mac to Latin-1, IBM page codes to Latin-1, Easy-French to Latin-1, remove Quoted-Printable, remove Base64.  These are so frequent that I made myself a few two-keystroke Emacs commands to filter the Emacs region.  This is very convenient for me.  I also resort to many other email conversions, yet more rarely than the frequent cases above.

     It seems like this should be doable using recode.  However, when I try something like grecode mac macfile.txt I get nothing out---no error, no output, nothing.

Presuming you are using some recent version of recode, the command:

     recode mac macfile.txt

is a request for recoding macfile.txt over itself, overwriting the original, from Macintosh usual character code and Macintosh end of lines, to Latin-1 and Unix end of lines.  This is overwrite mode.  If you want to use recode as a filter, which is probably what you need, rather do:

     recode mac

and give your Macintosh file as standard input, you'll get the Latin-1 file on standard output.  The above command is an abbreviation for any of:

     recode mac..
     recode mac..l1
     recode mac..Latin-1
     recode mac/CR..Latin-1/
     recode Macintosh..ISO_8859-1
     recode Macintosh/CR..ISO_8859-1/

That is, a CR surface, encoding newlines with ASCII CR, is first to be removed (this is a default surface for mac), then the Macintosh charset is converted to Latin-1 and no surface is added to the result (there is no default surface for l1).  If you want mac code converted, but you know that newlines are already coded the Unix way, just do:

     recode mac/

the slash then overriding the default surface with empty, that is, none. Here are other easy recipes:

     recode pc          to filter IBM-PC code and CR-LF (default) to Latin-1
     recode pc/         to filter IBM-PC code to Latin-1
     recode 850         to filter code page 850 and CR-LF (default) to Latin-1
     recode 850/        to filter code page 850 to Latin-1
     recode /qp         to remove quoted printable

The last one is indeed equivalent to any of:

     recode /qp..
     recode l1/qp..l1/
     recode ISO_8859-1/Quoted-Printable..ISO_8859-1/

Here are some reverse recipes:

     recode ..mac       to filter Latin-1 to Macintosh code and CR (default)
     recode ..mac/      to filter Latin-1 to Macintosh code
     recode ..pc        to filter Latin-1 to IBM-PC code and CR-LF (default)
     recode ..pc/       to filter Latin-1 to IBM-PC code
     recode ..850       to filter Latin-1 to code page 850 and CR-LF (default)
     recode ..850/      to filter Latin-1 to code page 850
     recode ../qp       to force quoted printable

In all the above calls, replace recode by recode -f if you want to proceed despite recoding errors.  If you do not use -f and there is an error, the recoding output will be interrupted after first error in filter mode, or the file will not be replaced by a recoded copy in overwrite mode.

You may use recode -l to get a list of available charsets and surfaces, and recode --help to get a quick summary of options. The above output is meant for those having already read this manual, so let me dare a suggestion: why could not you find a few more minutes in your schedule to peek further down, right into the following chapters!

Terminology and purpose
***********************

A few terms are used over and over in this manual, our wise reader will learn their meaning right away.  Both ISO (International Organization for Standardisation) and IETF (Internet Engineering Task Force) have their own terminology, this document does not try to stick to either one in a strict way, while it does not want to throw more confusion in the field. On the other hand, it would not be efficient using paraphrases all the time, so recode coins a few short words, which are explained below.

A charset, in the context of recode, is a particular association between computer codes on one side, and a repertoire of intended characters on the other side.  Codes are usually taken from a set of consecutive small integers, starting at 0.  Some characters have a graphical appearance (glyph) or displayable effect, others have special uses like, for example, to control devices or to interact with neighbouring codes to specify them more precisely.  So, a charset is roughly one of those tables, giving a meaning to each of the codes from the set of allowable values. MIME also uses the term charset with approximately the same meaning. It does not exactly corresponds to what ISO calls a coded character set, that is, a set of characters with an encoding for them. An coded character set does not necessarily use all available code positions, while a MIME charset usually tries to specify them all.  A MIME charset might be the union of a few disjoint coded character sets.

A surface is a term used in recode only, and is a short for surface transformation of a charset stream.  This is any kind of mapping, usually reversible, which associates physical bits in some medium for a stream of characters taken from one or more charsets (usually one). A surface is a kind of varnish added over a charset so it fits in actual bits and bytes.  How end of lines are exactly encoded is not really pertinent to the charset, and so, there is surface for end of lines. Base64 is also a surface, as we may encode any charset in it. Other examples would DES enciphering, or gzip compression (even if recode does not offer them currently): these are ways to give a real life to theoretical charsets.  The trivial surface consists into putting characters into fixed width little chunks of bits, usually eight such bits per character.  But things are not always that simple.

This recode library, and the program by that name, have the purpose of converting files between various charsets and surfaces.  When this cannot be done in exact ways, as it is often the case, the program may get rid of the offending characters or fall back on approximations. This library recognises or produces around 175 such charsets under 500 names, and handle a dozen surfaces.  Since it can convert each charset to almost any other one, many thousands of different conversions are possible.

The recode program and library do not usually know how to split and sort out textual and non-textual information which may be mixed in a single input file.  For example, there is no surface which currently addresses the problem of how lines are blocked into physical records, when the blocking information is added as binary markers or counters within files.  So, recode should be given textual streams which are rather pure.

This tool pays special attention to superimposition of diacritics for some French representations.  This orientation is mostly historical, it does not impair the usefulness, generality or extensibility of the program. recode is both a French and English word.  For those who pay attention to those things, the proper pronunciation is French (that is, racud, with a like in above, and u like in cut).

The program recode has been written by François Pinard. With time, it got to reuse works from other contributors, and notably, those of Keld Simonsen and Bruno Haible.

Overview of charsets
====================

Recoding is currently possible between many charsets, the bulk of which is described by RFC 1345 tables or available in the iconv library. See Tabular, and see libiconv.  The recode library also handles some charsets in some specialised ways.  These are:

  * 6-bit charsets based on CDC display code: 6/12 code from NOS; bang-bang code from Université de Montréal;

  * 7-bit ASCII: without any diacritics, or else: using backspace for overstriking; Unisys' Icon convention; TeX/LaTeX coding; easy French conventions for electronic mail;

  * 8-bit extensions to ASCII: ISO Latin-1, Atari ST code, IBM's code for the PC, Apple's code for the Macintosh;

  * 8-bit non-ASCII codes: three flavours of EBCDIC;

  * 16-bit or 31-bit universal characters, and their transfer encodings.

The introduction of RFC 1345 in recode has brought with it a few charsets having the functionality of older ones, but yet being different in subtle ways.  The effects have not been fully investigated yet, so for now, clashes are avoided, the old and new charsets are kept well separate.

Conversion is possible between almost any pair of charsets.  Here is a list of the exceptions.  One may not recode from the flat, count-characters or dump-with-names charsets, nor from or to the data, tree or :libiconv: charsets. Also, if we except the data and tree pseudo-charsets, charsets and surfaces live in disjoint recoding spaces, one cannot really transform a surface into a charset or vice-versa, as surfaces are only meant to be applied over charsets, or removed from them.

Overview of surfaces
====================

For various practical considerations, it sometimes happens that the codes making up a text, written in a particular charset, cannot simply be put out in a file one after another without creating problems or breaking other things.  Sometimes, 8-bit codes cannot be written on a 7-bit medium, variable length codes need kind of envelopes, newlines require special treatment, etc.  We sometimes have to apply surfaces to a stream of codes, which surfaces are kind of tricks used to fit the charset into those practical constraints.  Moreover, similar surfaces or tricks may be useful for many unrelated charsets, and many surfaces can be used at once over a single charset.

So, recode has machinery to describe a combination of a charset with surfaces used over it in a file.  We would use the expression pure charset for referring to a charset free of any surface, that is, the conceptual association between integer codes and character intents.

It is not always clear if some transformation will yield a charset or a surface, especially for those transformations which are only meaningful over a single charset.  The recode library is not overly picky as identifying surfaces as such: when it is practical to consider a specialised surface as if it were a charset, this is preferred, and done.

Contributions and bug reports
=============================

Even being the recode author and current maintainer, I am no specialist in charset standards.  I only made recode along the years to solve my own needs, but felt it was applicable for the needs of others.  Some FSF people liked the program structure and suggested to make it more widely available.  I often rely on recode users suggestions to decide what is best to be done next.

Properly protecting recode about possible copyright fights is a pain for me and for contributors, but we cannot avoid addressing the issue in the long run.  Besides, the Free Software Foundation, which mandates the GNU project, is very sensible to this matter.  GNU standards suggest that we stay cautious before looking at copyrighted code.  The safest and simplest way for me is to gather ideas and reprogram them anew, even if this might slow me down considerably.  For contributions going beyond a few lines of code here and there, the FSF definitely requires employer disclaimers and copyright assignments in writing.

When you contribute something to recode, please explain what it is about.  Do not take for granted that I know those charsets which are familiar to you.  Once again, I'm no expert, and you have to help me. Your explanations could well find their way into this documentation, too. Also, for contributing new charsets or new surfaces, as much as possible, please provide good, solid, verifiable references for the tables you used (I'm not prone at accepting a charset you just invented, and which nobody uses yet: convince your friends and community first!).

Many users contributed to recode already, I am grateful to them for their interest and involvement.  Some suggestions can be integrated quickly while some others have to be delayed, I have to draw a line somewhere when time comes to make a new release, about what would go in it and what would go in the next.

Please send suggestions, documentation errors and bug reports to recode-bugs@iro.umontreal.ca or, if you prefer, directly to pinard@iro.umontreal.ca, François Pinard.  Do not be afraid to report details, because this program is the mere aggregation of hundreds of details.

How to use this program
***********************

With the synopsis of the recode call, we stress the difference between using this program as a file filter, or recoding many files at once.  The first parameter of any call states the recoding request, and this deserves a section on its own.  Options are then presented, but somewhat grouped according to the related functionalities they control.

Synopsis of recode call
=======================

The general format of the program call is one of:

     recode [OPTION]... [CHARSET | REQUEST [FILE]... ]

Some calls are used only to obtain lists produced by recode itself, without actually recoding any file.  They are recognised through the usage of listing options, and these options decide what meaning should be given to an optional CHARSET parameter.  See Listings.

In other calls, the first parameter (REQUEST) always explains which transformations are expected on the files.  There are many variations to the aspect of this parameter.  We will discuss more complex situations later (see Requests), but for many simple cases, this parameter merely looks like this (In previous versions or recode, a single colon : was used instead of the two dots .. for separating charsets, but this was creating problems because colons are allowed in official charset names.  The old request syntax is still recognised for compatibility purposes, but is deprecated.):

     BEFORE..AFTER

where BEFORE and AFTER each gives the name of a charset.  Each FILE will be read assuming it is coded with charset BEFORE, it will be recoded over itself so to use the charset AFTER.  If there is no FILE on the recode command, the program rather acts as a Unix filter and transforms standard input onto standard output.

The capability of recoding many files at once is very convenient. For example, one could easily prepare a distribution from Latin-1 to MSDOS, this way:

     mkdir package
     cp -p Makefile *.[ch] package
     recode Latin-1..MSDOS package/*
     zoo ah package.zoo package/*
     rm -rf package

(In this example, the non-mandatory -p option to cp is for preserving timestamps, and the zoo program is an archiver from Rahul Dhesi which once was quite popular.)

The filter operation is especially useful when the input files should not be altered.  Let us make an example to illustrate this point. Suppose that someone has a file named datum.txt, which is almost a TeX file, except that diacriticised characters are written using Latin-1.  To complete the recoding of the diacriticised characters only and produce a file datum.tex, without destroying the original, one could do:

     cp -p datum.txt datum.tex
     recode -d l1..tex datum.tex

However, using recode as a filter will achieve the same goal more neatly:

     recode -d l1..tex <datum.txt >datum.tex

This example also shows that l1 could be used instead of Latin-1; charset names often have such aliases.

The REQUEST parameter
=====================

In the case where the REQUEST is merely written as BEFORE..AFTER, then BEFORE and AFTER specify the start charset and the goal charset for the recoding.

For recode, charset names may contain any character, besides a comma, a forward slash, or two periods in a row.  But in practice, charset names are currently limited to alphabetic letters (upper or lower case), digits, hyphens, underlines, periods, colons or round parentheses.

The complete syntax for a valid REQUEST allows for unusual things, which might surprise at first.  (Do not pay too much attention to these facilities on first reading.)  For example, REQUEST may also contain intermediate charsets, like in the following example:

     BEFORE..INTERIM1..INTERIM2..AFTER

meaning that recode should internally produce the INTERIM1 charset from the start charset, then work out of this INTERIM1 charset to internally produce INTERIM2, and from there towards the goal charset.  In fact, recode internally combines recipes and automatically uses interim charsets, when there is no direct recipe for transforming BEFORE into AFTER.  But there might be many ways to do it.  When many routes are possible, the above chaining syntax may be used to more precisely force the program towards a particular route, which it might not have naturally selected otherwise.  On the other hand, because recode tries to choose good routes, chaining is only needed to achieve some rare, unusual effects.

Moreover, many such requests (sub-requests, more precisely) may be separated with commas (but no spaces at all), indicating a sequence of recodings, where the output of one has to serve as the input of the following one.  For example, the two following requests are equivalent:

     BEFORE..INTERIM1..INTERIM2..AFTER
     BEFORE..INTERIM1,INTERIM1..INTERIM2,INTERIM2..AFTER

In this example, the charset input for any recoding sub-request is identical to the charset output by the preceding sub-request.  But it does not have to be so in the general case.  One might wonder what would be the meaning of declaring the charset input for a recoding sub-request of being of different nature than the charset output by a preceding sub-request, when recodings are chained in this way.  Such a strange usage might have a meaning and be useful for the recode expert, but they are quite uncommon in practice.

More useful is the distinction between the concept of charset, and the concept of surfaces.  An encoded charset is represented by:

     PURE-CHARSET/SURFACE1/SURFACE2...

using slashes to introduce surfaces, if any.  The order of application of surfaces is usually important, they cannot be freely commuted.  In the given example, SURFACE1 is first applied over the PURE-CHARSET, then SURFACE2 is applied over the result.  Given this request:

     BEFORE/SURFACE1/SURFACE2..AFTER/SURFACE3

the recode program will understand that the input files should have SURFACE2 removed first (because it was applied last), then SURFACE1 should be removed.  The next step will be to translate the codes from charset BEFORE to charset AFTER, prior to applying SURFACE3 over the result.

Some charsets have one or more implied surfaces.  In this case, the implied surfaces are automatically handled merely by naming the charset, without any explicit surface to qualify it.  Let's take an example to illustrate this feature.  The request pc..l1 will indeed decode MS-DOS end of lines prior to converting IBM-PC codes to Latin-1, because pc is the name of a charset (More precisely, pc is an alias for the charset IBM-PC.) which has CR-LF for its usual surface. The request pc/..l1 will not decode end of lines, since the slash introduces surfaces, and even if the surface list is empty, it effectively defeats the automatic removal of surfaces for this charset. So, empty surfaces are useful, indeed!

Both charsets and surfaces may have predefined alternate names, or aliases. However, and this is rather important to understand, implied surfaces are attached to individual aliases rather than on genuine charsets. Consequently, the official charset name and all of its aliases do not necessarily share the same implied surfaces.  The charset and all its aliases may each have its own different set of implied surfaces.

Charset names, surface names, or their aliases may always be abbreviated to any unambiguous prefix.  Internally in recode, disambiguating tables are kept separate for charset names and surface names.

While recognising a charset name or a surface name (or aliases thereof), recode ignores all characters besides letters and digits, so for example, the hyphens and underlines being part of an official charset name may safely be omitted (no need to un-confuse them!).  There is also no distinction between upper and lower case for charset or surface names.

One of the BEFORE or AFTER keywords may be omitted.  If the double dot separator is omitted too, then the charset is interpreted as the BEFORE charset. (Both BEFORE and AFTER may be omitted, in which case the double dot separator is mandatory.  This is not very useful, as the recoding reduces to a mere copy in that case.)

When a charset name is omitted or left empty, the value of the DEFAULT_CHARSET variable in the environment is used instead.  If this variable is not defined, the recode library uses the current locale's encoding. On POSIX compliant systems, this depends on the first non-empty value among the environment variables LC_ALL, LC_CTYPE, LANG, and can be determined through the command locale charmap.

If the charset name is omitted but followed by surfaces, the surfaces then qualify the usual or default charset.  For example, the request ../x is sufficient for applying an hexadecimal surface to the input text (MS-DOS is one of those systems for which the default charset has implied surfaces, CR-LF here.  Such surfaces are automatically removed or applied whenever the default charset is read or written, exactly as it would go for any other charset.  In the example above, on such systems, the hexadecimal surface would then replace the implied surfaces.  For adding an hexadecimal surface without removing any, one should write the request as /../x.).

The allowable values for BEFORE or AFTER charsets, and various surfaces, are described in the remainder of this document.

Asking for various lists
========================

Many options control listing output generated by recode itself, they are not meant to accompany actual file recodings.  These options are:

--version
     The program merely prints its version numbers on standard output, and exits without doing anything else.

--help
     The program merely prints a page of help on standard output, and exits without doing any recoding.

-C
--copyright
     Given this option, all other parameters and options are ignored.  The program prints briefly the copyright and copying conditions.  See the file COPYING in the distribution for full statement of the Copyright and copying conditions.

-h[LANGUAGE/][NAME]
--header[=[LANGUAGE/][NAME]]
     Instead of recoding files, recode writes a LANGUAGE source file on standard output and exits.  This source is meant to be included in a regular program written in the same programming LANGUAGE: its purpose is to declare and initialise an array, named NAME, which represents the requested recoding.  The only acceptable values for LANGUAGE are c or perl, and may may be abbreviated. If LANGUAGE is not specified, c is assumed.  If NAME is not specified, then it defaults to BEFORE_AFTER. Strings BEFORE and AFTER are cleaned before being used according to the syntax of LANGUAGE.

     Even if recode tries its best, this option does not always succeed in producing the requested source table.  It will however, provided the recoding can be internally represented by only one step after the optimisation phase, and if this merged step conveys a one-to-one or a one-to-many explicit table.  Also, when attempting to produce sources tables, recode relaxes its checking a tiny bit: it ignores the algorithmic part of some tabular recodings, it also avoids the processing of implied surfaces. But this is all fairly technical.  Better try and see!

     Beware that other options might affect the produced source tables, these are: -d, -g and, particularly, -s.

-k PAIRS
--known=PAIRS
     This particular option is meant to help identifying an unknown charset, using as hints some already identified characters of the charset.  Some examples will help introducing the idea.

     Let's presume here that recode is run in an ISO-8859-1 locale, and that DEFAULT_CHARSET is unset in the environment. Suppose you have guessed that code 130 (decimal) of the unknown charset represents a lower case e with an acute accent.  That is to say that this code should map to code 233 (decimal) in the usual charset. By executing:

          recode -k 130:233

     you should obtain a listing similar to:

          AtariST atarist
          CWI cphu cwi cwi2
          IBM437 437 cp437 ibm437
          IBM850 850 cp850 ibm850
          IBM851 851 cp851 ibm851
          IBM852 852 cp852 ibm852
          IBM857 857 cp857 ibm857
          IBM860 860 cp860 ibm860
          IBM861 861 cp861 cpis ibm861
          IBM863 863 cp863 ibm863
          IBM865 865 cp865 ibm865

     You can give more than one clue at once, to restrict the list further. Suppose you have also guessed that code 211 of the unknown charset represents an upper case E with diaeresis, that is, code 203 in the usual charset.  By requesting:

          recode -k 130:233,211:203

     you should obtain:

          IBM850 850 cp850 ibm850
          IBM852 852 cp852 ibm852
          IBM857 857 cp857 ibm857

     The usual charset may be overridden by specifying one non-option argument. For example, to request the list of charsets for which code 130 maps to code 142 for the Macintosh, you may ask:

          recode -k 130:142 mac

     and get:

          AtariST atarist
          CWI cphu cwi cwi2
          IBM437 437 cp437 ibm437
          IBM850 850 cp850 ibm850
          IBM851 851 cp851 ibm851
          IBM852 852 cp852 ibm852
          IBM857 857 cp857 ibm857
          IBM860 860 cp860 ibm860
          IBM861 861 cp861 cpis ibm861
          IBM863 863 cp863 ibm863
          IBM865 865 cp865 ibm865

     which, of course, is identical to the result of the first example, since the code 142 for the Macintosh is a small e with acute.

     More formally, option -k lists all possible before charsets for the after charset given as the sole non-option argument to recode, but subject to restrictions given in PAIRS.  If there is no non-option argument, the after charset is taken to be the default charset for this recode.

     The restrictions are given as a comma separated list of pairs, each pair consisting of two numbers separated by a colon.  The numbers are taken as decimal when the initial digit is between 1 and 9; 0x starts an hexadecimal number, or else 0 starts an octal number.  The first number is a code in any before charset, while the second number is a code in the specified after charset. If the first number would not be transformed into the second number by recoding from some before charset to the after charset, then this before charset is rejected.  A before charset is listed only if it is not rejected by any pair.  The program will only test those before charsets having a tabular style internal description (see Tabular), so should be the selected after charset.

     The produced list is in fact a subset of the list produced by the option -l.  As for option -l, the non-option argument is interpreted as a charset name, possibly abbreviated to any non ambiguous prefix.

-l[FORMAT]
--list[=FORMAT]
     This option asks for information about all charsets, or about one particular charset.  No file will be recoded.

     If there is no non-option arguments, recode ignores the FORMAT value of the option, it writes a sorted list of charset names on standard output, one per line.  When a charset name have aliases or synonyms, they follow the true charset name on its line, sorted from left to right. Each charset or alias is followed by its implied surfaces, if any.  This list is over two hundred lines.  It is best used with grep -i, as in:

          recode -l | grep -i greek

     There might be one non-option argument, in which case it is interpreted as a charset name, possibly abbreviated to any non ambiguous prefix. This particular usage of the -l option is obeyed only for charsets having a tabular style internal description (see Tabular). Even if most charsets have this property, some do not, and the option -l cannot be used to detail these particular charsets.  For knowing if a particular charset can be listed this way, you should merely try and see if this works.  The FORMAT value of the option is a keyword from the following list.  Keywords may be abbreviated by dropping suffix letters, and even reduced to the first letter only:

     decimal
          This format asks for the production on standard output of a concise tabular display of the charset, in which character code values are expressed in decimal.

     octal
          This format uses octal instead of decimal in the concise tabular display of the charset.

     hexadecimal
          This format uses hexadecimal instead of decimal in the concise tabular display of the charset.

     full
          This format requests an extensive display of the charset on standard output, using one line per character showing its decimal, hexadecimal, octal and UCS-2 code values, and also a descriptive comment which should be the 10646 name for the character.

          The descriptive comment is given in English and ASCII, yet if the English description is not available but a French one is, then the French description is given instead, using Latin-1.  However, if the LANGUAGE or LANG environment variable begins with the letters fr, then listing preference goes to French when both descriptions are available.

     When option -l is used together with a CHARSET argument, the FORMAT defaults to decimal.

-T
--find-subsets
     This option is a maintainer tool for evaluating the redundancy of those charsets, in recode, which are internally represented by an UCS-2 data table.  After the listing has been produced, the program exits without doing any recoding.  The output is meant to be sorted, like this: recode -T | sort.  The option triggers recode into comparing all pairs of charsets, seeking those which are subsets of others. The concept and results are better explained through a few examples. Consider these three sample lines from -T output:

          [  0] IBM891 == IBM903
          [  1] IBM1004 < CP1252
          [ 12] INVARIANT < CSA_Z243.4-1985-1

     The first line means that IBM891 and IBM903 are completely identical as far as recode is concerned, so one is fully redundant to the other.  The second line says that IBM1004 is wholly contained within CP1252, yet there is a single character which is in CP1252 without being in IBM1004.  The third line says that INVARIANT is wholly contained within CSA_Z243.4-1985-1, but twelve characters are in CSA_Z243.4-1985-1 without being in INVARIANT.  The whole output might most probably be reduced and made more significant through a transitivity study.

Controlling how files are recoded
=================================

The following options have the purpose of giving the user some fine grain control over the recoding operation themselves.

-c
--colons
     With Texte Easy French conventions, use the column : instead of the double-quote " for marking diaeresis. See Texte.

-g
--graphics
     This option is only meaningful while getting out of the IBM-PC charset.  In this charset, characters 176 to 223 are used for constructing rulers and boxes, using simple or double horizontal or vertical lines.  This option forces the automatic selection of ASCII characters for approximating these rulers and boxes, at cost of making the transformation irreversible.  Option -g implies -f.

-t
--touch
     The touch option is meaningful only when files are recoded over themselves.  Without it, the time-stamps associated with files are preserved, to reflect the fact that changing the code of a file does not really alter its informational contents.  When the user wants the recoded files to be time-stamped at the recoding time, this option inhibits the automatic protection of the time-stamps.

-v
--verbose
     Before doing any recoding, the program will first print on the stderr stream the list of all intermediate charsets planned for recoding, starting with the BEFORE charset and ending with the AFTER charset. It also prints an indication of the recoding quality, as one of the word reversible, one to one, one to many, many to one or many to many.

     This information will appear once or twice.  It is shown a second time only when the optimisation and step merging phase succeeds in replacing many single steps by a new one.

     This option also has a second effect.  The program will print on stderr one message per recoded FILE, so as to keep the user informed of the progress of its command.

     An easy way to know beforehand the sequence or quality of a recoding is by using the command such as:

          recode -v BEFORE..AFTER < /dev/null

     using the fact that, in recode, an empty input file produces an empty output file.

-x CHARSET
--ignore=CHARSET
     This option tells the program to ignore any recoding path through the specified CHARSET, so disabling any single step using this charset as a start or end point.  This may be used when the user wants to force recode into using an alternate recoding path (yet using chained requests offers a finer control, see Requests).

     CHARSET may be abbreviated to any unambiguous prefix.

Reversibility issues
====================

The following options are somewhat related to reversibility issues:

-f
--force
     With this option, irreversible or otherwise erroneous recodings are run to completion, and recode does not exit with a non-zero status if it would be only because irreversibility matters.  See Reversibility.

     Without this option, recode tries to protect you against recoding a file irreversibly over itself (There are still some cases of ambiguous output which are rather difficult to detect, and for which the protection is not active.).  Whenever an irreversible recoding is met, or any other recoding error, recode produces a warning on standard error.  The current input file does not get replaced by its recoded version, and recode then proceeds with the recoding of the next file.

     When the program is merely used as a filter, standard output will have received a partially recoded copy of standard input, up to the first error point.  After all recodings have been done or attempted, and if some recoding has been aborted, recode exits with a non-zero status.

     In releases of recode prior to version 3.5, this option was always selected, so it was rather meaningless.  Nevertheless, users were invited to start using -f right away in scripts calling recode whenever convenient, in preparation for the current behaviour.

-q
--quiet
--silent
     This option has the sole purpose of inhibiting warning messages about irreversible recodings, and other such diagnostics.  It has no other effect, in particular, it does not prevent recodings to be aborted or recode to return a non-zero exit status when irreversible recodings are met.

     This option is set automatically for the children processes, when recode splits itself in many collaborating copies.  Doing so, the diagnostic is issued only once by the parent.  See option -p.

-s
--strict
     By using this option, the user requests that recode be very strict while recoding a file, merely losing in the transformation any character which is not explicitly mapped from a charset to another.  Such a loss is not reversible and so, will bring recode to fail, unless the option -f is also given as a kind of counter-measure.

     Using -s without -f might render the recode program very susceptible to the slighest file abnormalities.  Despite the fact that it might be irritating to some users, such paranoia is sometimes wanted and useful.

Even if recode tries hard to keep the recodings reversible, you should not develop an unconditional confidence in its ability to do so.  You ought to keep only reasonable expectations about reverse recodings.  In particular, consider:

  * Most transformations are fully reversible for all inputs, but lose this property whenever -s is specified.

  * A few transformations are not meant to be reversible, by design.

  * Reversibility sometimes depends on actual file contents and cannot be ascertained beforehand, without reading the file.

  * Reversibility is never absolute across successive versions of this program.  Even correcting a small bug in a mapping could induce slight discrepancies later.

  * Reversibility is easily lost by merging.  This is best explained through an example.  If you reversibly recode a file from charset A to charset B, then you reversibly recode the result from charset B to charset C, you cannot expect to recover the original file by merely recoding from charset C directly to charset A. You will instead have to recode from charset C back to charset B, and only then from charset B to charset A.

  * Faulty files create a particular problem.  Consider an example, recoding from IBM-PC to Latin-1.  End of lines are represented as \r\n in IBM-PC and as \n in Latin-1.  There is no way by which a faulty IBM-PC file containing a \n not preceded by \r be translated into a Latin-1 file, and then back.

  * There is another difficulty arising from code equivalences.  For example, in a LaTeX charset file, the string \^\i{} could be recoded back and forth through another charset and become \^{\i}.  Even if the resulting file is equivalent to the original one, it is not identical.

Unless option -s is used, recode automatically tries to fill mappings with invented correspondences, often making them fully reversible.  This filling is not made at random.  The algorithm tries to stick to the identity mapping and, when this is not possible, it prefers generating many small permutation cycles, each involving only a few codes.

For example, here is how IBM-PC code 186 gets translated to control-U in Latin-1.  Control-U is 21.  Code 21 is the IBM-PC section sign, which is 167 in Latin-1.  recode cannot reciprocate 167 to 21, because 167 is the masculine ordinal indicator within IBM-PC, which is 186 in Latin-1.  Code 186 within IBM-PC has no Latin-1 equivalent; by assigning it back to 21, recode closes this short permutation loop.

As a consequence of this map filling, recode may sometimes produce funny characters.  They may look annoying, they are nevertheless helpful when one changes his (her) mind and wants to revert to the prior recoding.  If you cannot stand these, use option -s, which asks for a very strict recoding.

This map filling sometimes has a few surprising consequences, which some users wrongly interpreted as bugs.  Here are two examples.

 1. In some cases, recode seems to copy a file without recoding it. But in fact, it does.  Consider a request:

          recode l1..us < File-Latin1 > File-ASCII
          cmp File-Latin1 File-ASCII

     then cmp will not report any difference.  This is quite normal. Latin-1 gets correctly recoded to ASCII for charsets commonalities (which are the first 128 characters, in this case).  The remaining last 128 Latin-1 characters have no ASCII correspondent.  Instead of losing them, recode elects to map them to unspecified characters of ASCII, so making the recoding reversible.  The simplest way of achieving this is merely to keep those last 128 characters unchanged.  The overall effect is copying the file verbatim.

     If you feel this behaviour is too generous and if you do not wish to care about reversibility, simply use option -s.  By doing so, recode will strictly map only those Latin-1 characters which have an ASCII equivalent, and will merely drop those which do not.  Then, there is more chance that you will observe a difference between the input and the output file.

 2. Recoding the wrong way could sometimes give the false impression that recoding has almost been done properly.  Consider the requests:

          recode 437..l1 < File-Latin1 > Temp1
          recode 437..l1 < Temp1 > Temp2

     so declaring wrongly File-Latin1 to be an IBM-PC file, and recoding to Latin-1.  This is surely ill defined and not meaningful. Yet, if you repeat this step a second time, you might notice that many (not all) characters in Temp2 are identical to those in File-Latin1.  Sometimes, people try to discover how recode works by experimenting a little at random, rather than reading and understanding the documentation; results such as this are surely confusing, as they provide those people with a false feeling that they understood something.

     Reversible codings have this property that, if applied several times in the same direction, they will eventually bring any character back to its original value.  Since recode seeks small permutation cycles when creating reversible codings, besides characters unchanged by the recoding, most permutation cycles will be of length 2, and fewer of length 3, etc.  So, it is just expectable that applying the recoding twice in the same direction will recover most characters, but will fail to recover those participating in permutation cycles of length 3.  On the other end, recoding six times in the same direction would recover all characters in cycles of length 1, 2, 3 or 6.

Selecting sequencing methods
============================

This program uses a few techniques when it is discovered that many passes are needed to comply with the REQUEST.  For example, suppose that four elementary steps were selected at recoding path optimisation time.  Then recode will split itself into four different interconnected tasks, logically equivalent to:

     STEP1 <INPUT | STEP2 | STEP3 | STEP4 >OUTPUT

The splitting into subtasks is often done using Unix pipes. But the splitting may also be completely avoided, and rather simulated by using memory buffer, or intermediate files.  The various --sequence=STRATEGY options gives you control over the flow methods, by replacing STRATEGY with memory, pipe or files.  So, these options may be used to override the default behaviour, which is also explained below.

--sequence=memory
     When the recoding requires a combination of two or more elementary recoding steps, this option forces many passes over the data, using in-memory buffers to hold all intermediary results.

-i
--sequence=files
     When the recoding requires a combination of two or more elementary recoding steps, this option forces many passes over the data, using intermediate files between passes.  This is the default behaviour when files are recoded over themselves.  If this option is selected in filter mode, that is, when the program reads standard input and writes standard output, it might take longer for programs further down the pipe chain to start receiving some recoded data.

-p
--sequence=pipe
     When the recoding requires a combination of two or more elementary recoding steps, this option forces the program to fork itself into a few copies interconnected with pipes, using the pipe(2) system call. All copies of the program operate in parallel.  This is the default behaviour in filter mode.  If this option is used when files are recoded over themselves, this should also save disk space because some temporary files might not be needed, at the cost of more system overhead.

     If, at installation time, the pipe(2) call is said to be unavailable, selecting option -p is equivalent to selecting option -i.  (This happens, for example, on MS-DOS systems.)

Using mixed charset input
=========================

In real life and practice, textual files are often made up of many charsets at once.  Some parts of the file encode one charset, while other parts encode another charset, and so forth.  Usually, a file does not toggle between more than two or three charsets.  The means to distinguish which charsets are encoded at various places is not always available. The recode program is able to handle only a few simple cases of mixed input.

The default recode behaviour is to expect pure charset files, to be recoded as other pure charset files.  However, the following options allow for a few precise kinds of mixed charset files.

-d
--diacritics
     While converting to or from one of HTML or LaTeX charset, limit conversion to some subset of all characters. For HTML, limit conversion to the subset of all non-ASCII characters.  For LaTeX, limit conversion to the subset of all non-English letters.  This is particularly useful, for example, when people create what would be valid HTML, TeX or LaTeX files, if only they were using provided sequences for applying diacritics instead of using the diacriticised characters directly from the underlying character set.

     While converting to HTML or LaTeX charset, this option assumes that characters not in the said subset are properly coded or protected already, recode then transmit them literally. While converting the other way, this option prevents translating back coded or protected versions of characters not in the said subset. See HTML.  See LaTeX.

-S[LANGUAGE]
--source[=LANGUAGE]
     The bulk of the input file is expected to be written in ASCII, except for parts, like comments and string constants, which are written using another charset than ASCII.  When LANGUAGE is c, the recoding will proceed only with the contents of comments or strings, while everything else will be copied without recoding.  When LANGUAGE is po, the recoding will proceed only within translator comments (those having whitespace immediately following the initial #) and with the contents of msgstr strings.

     For the above things to work, the non-ASCII encoding of the comment or string should be such that an ASCII scan will successfully find where the comment or string ends.

     Even if ASCII is the usual charset for writing programs, some compilers are able to directly read other charsets, like UTF-8, say. There is currently no provision in recode for reading mixed charset sources which are not based on ASCII.  It is probable that the need for mixed recoding is not as pressing in such cases.

     For example, after one does:

          recode -Spo pc/..u8 < INPUT.po > OUTPUT.po

     file OUTPUT.po holds a copy of INPUT.po in which only translator comments and the contents of msgstr strings have been recoded from the IBM-PC charset to pure UTF-8, without attempting conversion of end-of-lines.  Machine generated comments and original msgid strings are not to be touched by this recoding.

     If LANGUAGE is not specified, c is assumed.

Using recode within Emacs
=========================

The fact recode is a filter makes it quite easy to use from within GNU Emacs.  For example, recoding the whole buffer from the IBM-PC charset to current charset (Latin-1 on Unix) is easily done with:

     C-x h C-u M-| recode ibmpc RET

C-x h selects the whole buffer, and C-u M-| filters and replaces the current region through the given shell command.  Here is another example, binding the keys C-c T to the recoding of the current region from Easy French to Latin-1 (on Unix) and the key C-u C-c T from Latin-1 (on Unix) to Easy French:

     (global-set-key "\C-cT" 'recode-texte)

     (defun recode-texte (flag)
       (interactive "P")
       (shell-command-on-region
        (region-beginning) (region-end)
        (concat "recode " (if flag "..txte" "txte")) t)
       (exchange-point-and-mark))

Debugging considerations
========================

It is our experience that when recode does not provide satisfying results, either recode was not called properly, correct results raised some doubts nevertheless, or files to recode were somewhat mangled. Genuine bugs are surely possible.

Unless you already are a recode expert, it might be a good idea to quickly revisit the tutorial (see Tutorial) or the prior sections in this chapter, to make sure that you properly formatted your recoding request. In the case you intended to use recode as a filter, make sure that you did not forget to redirect your standard input (through using the < symbol in the shell, say).  Some recode false mysteries are also easily explained, see Reversibility.

For the other cases, some investigation is needed.  To illustrate how to proceed, let's presume that you want to recode the nicepage file, coded UTF-8, into HTML.  The problem is that the command recode u8..h nicepage yields:

     recode: Invalid input in step `UTF-8..ISO-10646-UCS-2'

One good trick is to use recode in filter mode instead of in file replacement mode, see Synopsis.  Another good trick is to use the -v option asking for a verbose description of the recoding steps. We could rewrite our recoding call as recode -v u8..h <nicepage, to get something like:

     Request: UTF-8..:libiconv:..ISO-10646-UCS-2..HTML_4.0
     Shrunk to: UTF-8..ISO-10646-UCS-2..HTML_4.0
     [...SOME OUTPUT...]
     recode: Invalid input in step `UTF-8..ISO-10646-UCS-2'

This might help you to better understand what the diagnostic means.  The recoding request is achieved in two steps, the first recodes UTF-8 into UCS-2, the second recodes UCS-2 into HTML. The problem occurs within the first of these two steps, and since, the input of this step is the input file given to recode, this is this overall input file which seems to be invalid.  Also, when used in filter mode, recode processes as much input as possible before the error occurs and sends the result of this processing to standard output. Since the standard output has not been redirected to a file, it is merely displayed on the user screen.  By inspecting near the end of the resulting HTML output, that is, what was recoding a bit before the recoding was interrupted, you may infer about where the error stands in the real UTF-8 input file.

If you have the proper tools to examine the intermediate recoding data, you might also prefer to reduce the problem to a single step to better study it.  This is what I usually do.  For example, the last recode call above is more or less equivalent to:

     recode -v UTF-8..ISO_10646-UCS-2 <nicepage >temporary
     recode -v ISO_10646-UCS-2..HTML_4.0 <temporary
     rm temporary

If you know that the problem is within the first step, you might prefer to concentrate on using the first recode line.  If you know that the problem is within the second step, you might execute the first recode line once and for all, and then play with the second recode call, repeatedly using the temporary file created once by the first call.

Note that the -f switch may be used to force the production of HTML output despite invalid input, it might be satisfying enough for you, and easier than repairing the input file.  That depends on how strict you would like to be about the precision of the recoding process.

If you later see that your HTML file begins with @lt;html@gt; when you expected <html>, then recode might have done a bit more that you wanted.  In this case, your input file was half-UTF-8, half-HTML already, that is, a mixed file (see Mixed).  There is a special -d switch for this case.  So, your might be end up calling recode -fd nicepage.  Until you are quite sure that you accept overwriting your input file whatever what, I recommend that you stick with filter mode.

If, after such experiments, you seriously think that the recode program does not behave properly, there might be a genuine bug in the program itself, in which case I invite you to to contribute a bug report, see Contributing.

A recoding library
******************

The program named recode is just an application of its recoding library.  The recoding library is available separately for other C programs.  A good way to acquire some familiarity with the recoding library is to get acquainted with the recode program itself.

To use the recoding library once it is installed, a C program needs to have a line:

     #include <recode.h>

near its beginning, and the user should have -lrecode on the linking call, so modules from the recoding library are found.

The library is still under development.  As it stands, it contains four identifiable sets of routines: the outer level functions, the request level functions, the task level functions and the charset level functions. There are discussed in separate sections.

For effectively using the recoding library in most applications, it should be rarely needed to study anything beyond the main initialisation function at outer level, and then, various functions at request level.

Outer level functions
=====================

The outer level functions mainly prepare the whole recoding library for use, or do actions which are unrelated to specific recodings.  Here is an example of a program which does not really make anything useful.

     #include <stdbool.h>
     #include <recode.h>

     const char *program_name;

     int
     main (int argc, char *const *argv)
     {
       program_name = argv[0];
       RECODE_OUTER outer = recode_new_outer (true);

       recode_delete_outer (outer);
       exit (0);
     }

The header file <recode.h> declares an opaque RECODE_OUTER structure, which the programmer should use for allocating a variable in his program (let's assume the programmer is a male, here, no prejudice intended).  This outer variable is given as a first argument to all outer level functions.

The <recode.h> header file uses the Boolean type setup by the system header file <stdbool.h>.  But this header file is still fairly new in C standards, and likely does not exist everywhere.  If you system does not offer this system header file yet, the proper compilation of the <recode.h> file could be guaranteed through the replacement of the inclusion line by:

     typedef enum {false = 0, true = 1} bool;

People wanting wider portability, or Autoconf lovers, might arrange their configure.in for being able to write something more general, like:

     #if STDC_HEADERS
     # include <stdlib.h>
     #endif

     /* Some systems do not define EXIT_*, even with STDC_HEADERS.  */
     #ifndef EXIT_SUCCESS
     # define EXIT_SUCCESS 0
     #endif
     #ifndef EXIT_FAILURE
     # define EXIT_FAILURE 1
     #endif
     /* The following test is to work around the gross typo in systems like Sony
        NEWS-OS Release 4.0C, whereby EXIT_FAILURE is defined to 0, not 1.  */
     #if !EXIT_FAILURE
     # undef EXIT_FAILURE
     # define EXIT_FAILURE 1
     #endif

     #if HAVE_STDBOOL_H
     # include <stdbool.h>
     #else
     typedef enum {false = 0, true = 1} bool;
     #endif

     #include <recode.h>

     const char *program_name;

     int
     main (int argc, char *const *argv)
     {
       program_name = argv[0];
       RECODE_OUTER outer = recode_new_outer (true);

       recode_term_outer (outer);
       exit (EXIT_SUCCESS);
     }

but we will not insist on such details in the examples to come.

  * Initialisation functions

          RECODE_OUTER recode_new_outer (AUTO_ABORT);
          bool recode_delete_outer (OUTER);

     The recoding library absolutely needs to be initialised before being used, and recode_new_outer has to be called once, first.  Besides the OUTER it is meant to initialise, the function accepts a Boolean argument whether or not the library should automatically issue diagnostics on standard and abort the whole program on errors.  When AUTO_ABORT is true, the library later conveniently issues diagnostics itself, and aborts the calling program on errors.  This is merely a convenience, because if this parameter was false, the calling program should always take care of checking the return value of all other calls to the recoding library functions, and when any error is detected, issue a diagnostic and abort processing itself.

     Regardless of the setting of AUTO_ABORT, all recoding library functions return a success status.  Most functions are geared for returning false for an error, and true if everything went fine. Functions returning structures or strings return NULL instead of the result, when the result cannot be produced.  If AUTO_ABORT is selected, functions either return true, or do not return at all.

     As in the example above, recode_new_outer is called only once in most cases.  Calling recode_new_outer implies some overhead, so calling it more than once should preferably be avoided.

     The termination function recode_delete_outer reclaims the memory allocated by recode_new_outer for a given OUTER variable. Calling recode_delete_outer prior to program termination is more aesthetic then useful, as all memory resources are automatically reclaimed when the program ends.  You may spare this terminating call if you prefer.

  * The program_name declaration

     As we just explained, the user may set the recode library so that, in case of problems error, it issues the diagnostic itself and aborts the whole processing.  This capability may be quite convenient.  When this feature is used, the aborting routine includes the name of the running program in the diagnostic.  On the other hand, when this feature is not used, the library merely return error codes, giving the library user fuller control over all this.  This behaviour is more like what usual libraries do: they return codes and never abort.  However, I would rather not force library users to necessarily check all return codes themselves, by leaving no other choice.  In most simple applications, letting the library diagnose and abort is much easier, and quite welcome.  This is precisely because both possibilities exist that the program_name variable is needed: it may be used by the library when the user sets it to diagnose itself.

Request level functions
=======================

The request level functions are meant to cover most recoding needs programmers may have; they should provide all usual functionality. Their API is almost stable by now.  To get started with request level functions, here is a full example of a program which sole job is to filter ibmpc code on its standard input into latin1 code on its standard output.

     #include <stdio.h>
     #include <stdbool.h>
     #include <recode.h>

     const char *program_name;

     int
     main (int argc, char *const *argv)
     {
       program_name = argv[0];
       RECODE_OUTER outer = recode_new_outer (true);
       RECODE_REQUEST request = recode_new_request (outer);
       bool success;

       recode_scan_request (request, "ibmpc..latin1");

       success = recode_file_to_file (request, stdin, stdout);

       recode_delete_request (request);
       recode_delete_outer (outer);

       exit (success ? 0 : 1);
     }

The header file <recode.h> declares a RECODE_REQUEST structure, which the programmer should use for allocating a variable in his program. This REQUEST variable is given as a first argument to all request level functions, and in most cases, may be considered as opaque.

  * Initialisation functions

          RECODE_REQUEST recode_new_request (OUTER);
          bool recode_delete_request (REQUEST);

     No REQUEST variable may not be used in other request level functions of the recoding library before having been initialised by recode_new_request.  There may be many such REQUEST variables, in which case, they are independent of one another and they all need to be initialised separately.  To avoid memory leaks, a REQUEST variable should not be initialised a second time without calling recode_delete_request to ``un-initialise'' it.

     Like for recode_delete_outer, calling recode_delete_request prior to program termination, in the example above, may be left out.

  * Fields of struct recode_request

     Here are the fields of a struct recode_request which may be meaningfully changed, once a REQUEST has been initialised by recode_new_request, but before it gets used.  It is not very frequent, in practice, that these fields need to be changed.  To access the fields, you need to include recodext.h instead of recode.h, in which case there also is a greater chance that you need to recompile your programs if a new version of the recoding library gets installed.

     verbose_flag
          This field is initially false.  When set to true, the library will echo to stderr the sequence of elementary recoding steps needed to achieve the requested recoding.

     diaeresis_char
          This field is initially the ASCII value of a double quote ", but it may also be the ASCII value of a colon :.  In texte charset, some countries use double quotes to mark diaeresis, while other countries prefer colons.  This field contains the diaeresis character for the texte charset.

     make_header_flag
          This field is initially false.  When set to true, it indicates that the program is merely trying to produce a recoding table in source form rather than completing any actual recoding.  In such a case, the optimisation of step sequence can be attempted much more aggressively. If the step sequence cannot be reduced to a single step, table production will fail.

     diacritics_only
          This field is initially false.  For HTML and LaTeX charset, it is often convenient to recode the diacriticized characters only, while just not recoding other HTML code using ampersands or angular brackets, or LaTeX code using backslashes.  Set the field to true for getting this behaviour.  In the other charset, one can edit text as well as HTML or LaTeX directives.

     ascii_graphics
          This field is initially false, and relate to characters 176 to 223 in the ibmpc charset, which are use to draw boxes.  When set to true, while getting out of ibmpc, ASCII characters are selected so to graphically approximate these boxes.

  * Study of request strings

          bool recode_scan_request (REQUEST, "STRING");

     The main role of a REQUEST variable is to describe a set of recoding transformations.  Function recode_scan_request studies the given STRING, and stores an internal representation of it into REQUEST.  Note that STRING may be a full-fledged recode request, possibly including surfaces specifications, intermediary charsets, sequences, aliases or abbreviations (see Requests).

     The internal representation automatically receives some pre-conditioning and optimisation, so the REQUEST may then later be used many times to achieve many actual recodings.  It would not be efficient calling recode_scan_request many times with the same STRING, it is better having many REQUEST variables instead.

  * Actual recoding jobs

     Once the REQUEST variable holds the description of a recoding transformation, a few functions use it for achieving an actual recoding. Either input or output of a recoding may be string, an in-memory buffer, or a file.

     Functions with names like recode_INPUT-TYPE_to_OUTPUT-TYPE request an actual recoding, and are described below.  It is easy to remember which arguments each function accepts, once grasped some simple principles for each possible TYPE.  However, one of the recoding function escapes these principles and is discussed separately, first.

          recode_string (REQUEST, STRING);

     The function recode_string recodes STRING according to REQUEST, and directly returns the resulting recoded string freshly allocated, or NULL if the recoding could not succeed for some reason.  When this function is used, it is the responsibility of the programmer to ensure that the memory used by the returned string is later reclaimed.

          char *recode_string_to_buffer (REQUEST,
            INPUT_STRING,
            &OUTPUT_BUFFER, &OUTPUT_LENGTH, &OUTPUT_ALLOCATED);
          bool recode_string_to_file (REQUEST,
            INPUT_FILE,
            OUTPUT_FILE);
          bool recode_buffer_to_buffer (REQUEST,
            INPUT_BUFFER, INPUT_LENGTH,
            &OUTPUT_BUFFER, &OUTPUT_LENGTH, &OUTPUT_ALLOCATED);
          bool recode_buffer_to_file (REQUEST,
            INPUT_BUFFER, INPUT_LENGTH,
            OUTPUT_FILE);
          bool recode_file_to_buffer (REQUEST,
            INPUT_FILE,
            &OUTPUT_BUFFER, &OUTPUT_LENGTH, &OUTPUT_ALLOCATED);
          bool recode_file_to_file (REQUEST,
            INPUT_FILE,
            OUTPUT_FILE);

     All these functions return a bool result, false meaning that the recoding was not successful, often because of reversibility issues. The name of the function well indicates on which types it reads and which type it produces.  Let's discuss these three types in turn.

     string

          A string is merely an in-memory buffer which is terminated by a NUL character (using as many bytes as needed), instead of being described by a byte length.  For input, a pointer to the buffer is given through one argument.

          It is notable that there is no to_string functions.  Only one function recodes into a string, and it is recode_string, which has already been discussed separately, above.

     buffer

          A buffer is a sequence of bytes held in computer memory.  For input, two arguments provide a pointer to the start of the buffer and its byte size. Note that for charsets using many bytes per character, the size is given in bytes, not in characters.

          For output, three arguments provide the address of three variables, which will receive the buffer pointer, the used buffer size in bytes, and the allocated buffer size in bytes.  If at the time of the call, the buffer pointer is NULL, then the allocated buffer size should also be zero, and the buffer will be allocated afresh by the recoding functions.  However, if the buffer pointer is not NULL, it should be already allocated, the allocated buffer size then gives its size.  If the allocated size gets exceeded while the recoding goes, the buffer will be automatically reallocated bigger, probably elsewhere, and the allocated buffer size will be adjusted accordingly.

          The second variable, giving the in-memory buffer size, will receive the exact byte size which was needed for the recoding.  A NUL character is guaranteed at the end of the produced buffer, but is not counted in the byte size of the recoding.  Beyond that NUL, there might be some extra space after the recoded data, extending to the allocated buffer size.

     file

          A file is a sequence of bytes held outside computer memory, but buffered through it.  For input, one argument provides a pointer to a file already opened for read.  The file is then read and recoded from its current position until the end of the file, effectively swallowing it in memory if the destination of the recoding is a buffer.  For reading a file filtered through the recoding library, but only a little bit at a time, one should rather use recode_filter_open and recode_filter_close (these two functions are not yet available).

          For output, one argument provides a pointer to a file already opened for write.  The result of the recoding is written to that file starting at its current position.

The following special function is still subject to change:

     void recode_format_table (REQUEST, LANGUAGE, "NAME");

and is not documented anymore for now.

Task level functions
====================

The task level functions are used internally by the request level functions, they allow more explicit control over files and memory buffers holding input and output to recoding processes.  The interface specification of task level functions is still subject to change a bit.

To get started with task level functions, here is a full example of a program which sole job is to filter ibmpc code on its standard input into latin1 code on its standard output.  That is, this program has the same goal as the one from the previous section, but does its things a bit differently.

     #include <stdio.h>
     #include <stdbool.h>
     #include <recodext.h>

     const char *program_name;

     int
     main (int argc, char *const *argv)
     {
       program_name = argv[0];
       RECODE_OUTER outer = recode_new_outer (false);
       RECODE_REQUEST request = recode_new_request (outer);
       RECODE_TASK task;
       bool success;

       recode_scan_request (request, "ibmpc..latin1");

       task = recode_new_task (request);
       task->input.file = "";
       task->output.file = "";
       success = recode_perform_task (task);

       recode_delete_task (task);
       recode_delete_request (request);
       recode_delete_outer (outer);

       exit (success ? 0 : 1);
     }

The header file <recode.h> declares a RECODE_TASK structure, which the programmer should use for allocating a variable in his program.  This task variable is given as a first argument to all task level functions.  The programmer ought to change and possibly consult a few fields in this structure, using special functions.

  * Initialisation functions

          RECODE_TASK recode_new_task (REQUEST);
          bool recode_delete_task (TASK);

     No TASK variable may be used in other task level functions of the recoding library without having first been initialised with recode_new_task.  There may be many such TASK variables, in which case, they are independent of one another and they all need to be initialised separately.  To avoid memory leaks, a TASK variable should not be initialised a second time without calling recode_delete_task to ``un-initialise'' it.  This function also accepts a REQUEST argument and associates the request to the task.  In fact, a task is essentially a set of recoding transformations with the specification for its current input and its current output.

     The REQUEST variable may be scanned before or after the call to recode_new_task, it does not matter so far.  Immediately after initialisation, before further changes, the TASK variable associates REQUEST empty in-memory buffers for both input and output. The output buffer will later get allocated automatically on the fly, as needed, by various task processors.

     Even if a call to recode_delete_task is not strictly mandatory before ending the program, it is cleaner to always include it.  Moreover, in some future version of the recoding library, it might become required.

  * Fields of struct task_request

     Here are the fields of a struct task_request which may be meaningfully changed, once a TASK has been initialised by recode_new_task. In fact, fields are expected to change.  Once again, to access the fields, you need to include recodext.h instead of recode.h, in which case there also is a greater chance that you need to recompile your programs if a new version of the recoding library gets installed.

     request

          The field request points to the current recoding request, but may be changed as needed between recoding calls, for example when there is a need to achieve the construction of a resulting text made up of many pieces, each being recoded differently.

     input.name
     input.file

          If input.name is not NULL at start of a recoding, this is a request that a file by that name be first opened for reading and later automatically closed once the whole file has been read. If the file name is not NULL but an empty string, it means that standard input is to be used.  The opened file pointer is then held into input.file.

          If input.name is NULL and input.file is not, than input.file should point to a file already opened for read, which is meant to be recoded.

     input.buffer
     input.cursor
     input.limit

          When both input.name and input.file are NULL, three pointers describe an in-memory buffer containing the text to be recoded. The buffer extends from input.buffer to input.limit, yet the text to be recoded only extends from input.cursor to input.limit.  In most situations, input.cursor starts with the value that input.buffer has.  (Its value will internally advance as the recoding goes, until it reaches the value of input.limit.)

     output.name
     output.file

          If output.name is not NULL at start of a recoding, this is a request that a file by that name be opened for write and later automatically closed after the recoding is done.  If the file name is not NULL but an empty string, it means that standard output is to be used.  The opened file pointer is then held into output.file. If several passes with intermediate files are needed to produce the recoding, the output.name file is opened only for the final pass.

          If output.name is NULL and output.file is not, then output.file should point to a file already opened for write, which will receive the result of the recoding.

     output.buffer
     output.cursor
     output.limit

          When both output.name and output.file are NULL, three pointers describe an in-memory buffer meant to receive the text, once it is recoded.  The buffer is already allocated from output.buffer to output.limit.  In most situations, output.cursor starts with the value that output.buffer has.  Once the recoding is done, output.cursor will point at the next free byte in the buffer, just after the recoded text, so another recoding could be called without changing any of these three pointers, for appending new information to it. The number of recoded bytes in the buffer is the difference between output.cursor and output.buffer.

          Each time output.cursor reaches output.limit, the buffer is reallocated bigger, possibly at a different location in memory, always held up-to-date in output.buffer.  It is still possible to call a task level function with no output buffer at all to start with, in which case all three fields should have NULL as a value.  This is the situation immediately after a call to recode_new_task.

     strategy
          This field, which is of type enum recode_sequence_strategy, tells how various recoding steps (passes) will be interconnected.  Its initial value is RECODE_STRATEGY_UNDECIDED, which is a constant defined in the header file <recodext.h>.  Other possible values are:

          RECODE_SEQUENCE_IN_MEMORY
               Keep intermediate recodings in memory.

          RECODE_SEQUENCE_WITH_FILES
               Do not fork, use intermediate files.

          RECODE_SEQUENCE_WITH_PIPE
               Fork processes connected with pipe(2).

          The best for now is to leave this field alone, and let the recoding library decide its strategy, as many combinations have not been tested yet.

     byte_order_mark
          This field, which is preset to true, indicates that a byte order mark is to be expected at the beginning of any canonical UCS-2 or UTF-16 text, and that such a byte order mark should be also produced for these charsets.

     fail_level
          This field, which is of type enum recode_error (see Errors), sets the error level at which task level functions should report a failure. If an error being detected is equal or greater than fail_level, the function will eventually return false instead of true. The preset value for this field is RECODE_NOT_CANONICAL, that means that if not reset to another value, the library will report failure on any error.

     abort_level
          This field, which is of type enum recode_error (see Errors), sets the error level at which task level functions should immediately interrupt their processing.  If an error being detected is equal or greater than abort_level, the function returns immediately, but the returned value (true or false) is still is decided from the setting of fail_level, not abort_level.  The preset value for this field is RECODE_MAXIMUM_ERROR, that means that is not reset to another value, the library will never interrupt a recoding task.

     error_so_far
          This field, which is of type enum recode_error (see Errors), maintains the maximum error level met so far while the recoding task was proceeding.  The preset value is RECODE_NO_ERROR.

  * Task execution

          recode_perform_task (TASK);
          recode_filter_open (TASK, FILE);
          recode_filter_close (TASK);

     The function recode_perform_task reads as much input as possible, and recode all of it on prescribed output, given a properly initialised TASK.

     Functions recode_filter_open and recode_filter_close are only planned for now.  They are meant to read input in piecemeal ways. Even if functionality already exists informally in the library, it has not been made available yet through such interface functions.

Charset level functions
=======================

Many functions are internal to the recoding library.  Some of them have been made external and available, for the recode program had to retain all its previous functionality while being transformed into a mere application of the recoding library.  These functions are not really documented here for the time being, as we hope that many of them will vanish over time.  When this set of routines will stabilise, it would be convenient to document them as an API for handling charset names and contents.

     RECODE_CHARSET find_charset (NAME, CLEANING-TYPE);
     bool list_all_charsets (CHARSET);
     bool list_concise_charset (CHARSET, LIST-FORMAT);
     bool list_full_charset (CHARSET);

Handling errors
===============

The recode program, while using the recode library, needs to control whether recoding problems are reported or not, and then reflect these in the exit status.  The program should also instruct the library whether the recoding should be abruptly interrupted when an error is met (so sparing processing when it is known in advance that a wrong result would be discarded anyway), or if it should proceed nevertheless. Here is how the library groups errors into levels, listed here in order of increasing severity.

RECODE_NO_ERROR

     No error was met on previous library calls.

RECODE_NOT_CANONICAL

     The input text was using one of the many alternative codings for some phenomenon, but not the one recode would have canonically generated. So, if the reverse recoding is later attempted, it would produce a text having the same meaning as the original text, yet not being byte identical.

     For example, a Base64 block in which end-of-lines appear elsewhere that at every 76 characters is not canonical.  An e-circumflex in TeX which is coded as \^{e} instead of \^e is not canonical.

RECODE_AMBIGUOUS_OUTPUT

     It has been discovered that if the reverse recoding was attempted on the text output by this recoding, we would not obtain the original text, only because an ambiguity was generated by accident in the output text. This ambiguity would then cause the wrong interpretation to be taken.

     Here are a few examples.  If the Latin-1 sequence e^ is converted to Easy French and back, the result will be interpreted as e-circumflex and so, will not reflect the intent of the original two characters.  Recoding an IBM-PC text to Latin-1 and back, where the input text contained an isolated LF, will have a spurious CR inserted before the LF.

     Currently, there are many cases in the library where the production of ambiguous output is not properly detected, as it is sometimes a difficult problem to accomplish this detection, or to do it speedily.

RECODE_UNTRANSLATABLE

     One or more input character could not be recoded, because there is just no representation for this character in the output charset.

     Here are a few examples.  Non-strict mode often allows recode to compute on-the-fly mappings for unrepresentable characters, but strict mode prohibits such attribution of reversible translations: so strict mode might often trigger such an error.  Most UCS-2 codes used to represent Asian characters cannot be expressed in various Latin charsets.

RECODE_INVALID_INPUT

     The input text does not comply with the coding it is declared to hold.  So, there is no way by which a reverse recoding would reproduce this text, because recode should never produce invalid output.

     Here are a few examples.  In strict mode, ASCII text is not allowed to contain characters with the eight bit set.  UTF-8 encodings ought to be minimal (The minimality of an UTF-8 encoding is guaranteed on output, but currently, it is not checked on input.).

RECODE_SYSTEM_ERROR

     The underlying system reported an error while the recoding was going on, likely an input/output error. (This error symbol is currently unused in the library.)

RECODE_USER_ERROR

     The programmer or user requested something the recoding library is unable to provide, or used the API wrongly. (This error symbol is currently unused in the library.)

RECODE_INTERNAL_ERROR

     Something really wrong, which should normally never happen, was detected within the recoding library.  This might be due to genuine bugs in the library, or maybe due to un-initialised or overwritten arguments to the API. (This error symbol is currently unused in the library.)

RECODE_MAXIMUM_ERROR

     This error code should never be returned, it is only internally used as a sentinel for the list of all possible error codes.

One should be able to set the error level threshold for returning failure at end of recoding, and also the threshold for immediate interruption. If many errors occur while the recoding proceed, which are not severe enough to interrupt the recoding, then the most severe error is retained, while others are forgotten (Another approach would have been to define the level symbols as masks instead, and to give masks to threshold setting routines, and to retain all errors---yet I never met myself such a need in practice, and so I fear it would be overkill. On the other hand, it might be interesting to maintain counters about how many times each kind of error occurred.).  So, in case of an error, the possible actions currently are:

  * do nothing and let go, returning success at end of recoding,

  * just let go for now, but return failure at end of recoding,

  * interrupt recoding right away and return failure now.

See Task level, and particularly the description of the fields fail_level, abort_level and error_so_far, for more information about how errors are handled.

The universal charset
*********************

Standard ISO 10646 defines a universal character set, intended to encompass in the long run all languages written on this planet.  It is based on wide characters, and offer possibilities for two billion characters (2^31).

This charset was to become available in recode under the name UCS, with many external surfaces for it.  But in the current version, only surfaces of UCS are offered, each presented as a genuine charset rather than a surface.  Such surfaces are only meaningful for the UCS charset, so it is not that useful to draw a line between the surfaces and the only charset to which they may apply.

UCS stands for Universal Character Set.  UCS-2 and UCS-4 are fixed length encodings, using two or four bytes per character respectively.  UTF stands for UCS Transformation Format, and are variable length encodings dedicated to UCS. UTF-1 was based on ISO 2022, it did not succeed (It is not probable that recode will ever support UTF-1.).  UTF-2 replaced it, it has been called UTF-FSS (File System Safe) in Unicode or Plan9 context, but is better known today as UTF-8. To complete the picture, there is UTF-16 based on 16 bits bytes, and UTF-7 which is meant for transmissions limited to 7-bit bytes. Most often, one might see UTF-8 used for external storage, and UCS-2 used for internal storage.

When recode is producing any representation of UCS, it uses the replacement character U+FFFD for any valid character which is not representable in the goal charset (This is when the goal charset allows for 16-bits.  For shorter charsets, the --strict (-s) option decides what happens: either the character is dropped, or a reversible mapping is produced on the fly.). This happens, for example, when UCS-2 is not capable to echo a wide UCS-4 character, or for a similar reason, an UTF-8 sequence using more than three bytes.  The replacement character is meant to represent an existing character.  So, it is never produced to represent an invalid sequence or ill-formed character in the input text. In such cases, recode just gets rid of the noise, while taking note of the error in its usual ways.

Even if UTF-8 is an encoding, really, it is the encoding of a single character set, and nothing else.  It is useful to distinguish between an encoding (a surface within recode) and a charset, but only when the surface may be applied to several charsets.  Specifying a charset is a bit simpler than specifying a surface in a recode request. There would not be a practical advantage at imposing a more complex syntax to recode users, when it is simple to assimilate UTF-8 to a charset.  Similar considerations apply for UCS-2, UCS-4, UTF-16 and UTF-7.  These are all considered to be charsets.

Universal Character Set, 2 bytes
================================

One surface of UCS is usable for the subset defined by its first sixty thousand characters (in fact, 31 * 2^11 codes), and uses exactly two bytes per character.  It is a mere dump of the internal memory representation which is natural for this subset and as such, conveys with it endianness problems.

A non-empty UCS-2 file normally begins with a so called byte order mark, having value 0xFEFF.  The value 0xFFFE is not an UCS character, so if this value is seen at the beginning of a file, recode reacts by swapping all pairs of bytes.  The library also properly reacts to other occurrences of 0xFEFF or 0xFFFE elsewhere than at the beginning, because concatenation of UCS-2 files should stay a simple matter, but it might trigger a diagnostic about non canonical input.

By default, when producing an UCS-2 file, recode always outputs the high order byte before the low order byte.  But this could be easily overridden through the 21-Permutation surface (see Permutations).  For example, the command:

     recode u8..u2/21 < INPUT > OUTPUT

asks for an UTF-8 to UCS-2 conversion, with swapped byte output.

Use UCS-2 as a genuine charset.  This charset is available in recode under the name ISO-10646-UCS-2.  Accepted aliases are UCS-2, BMP, rune and u2.

The recode library is able to combine UCS-2 some sequences of codes into single code characters, to represent a few diacriticized characters, ligatures or diphtongs which have been included to ease mapping with other existing charsets.  It is also able to explode such single code characters into the corresponding sequence of codes. The request syntax for triggering such operations is rudimentary and temporary.  The combined-UCS-2 pseudo character set is a special form of UCS-2 in which known combinings have been replaced by the simpler code.  Using combined-UCS-2 instead of UCS-2 in an after position of a request forces a combining step, while using combined-UCS-2 instead of UCS-2 in a before position of a request forces an exploding step.  For the time being, one has to resort to advanced request syntax to achieve other effects.  For example:

     recode u8..co,u2..u8 < INPUT > OUTPUT

copies an UTF-8 INPUT over OUTPUT, still to be in UTF-8, yet merging combining characters into single codes whenever possible.

Universal Character Set, 4 bytes
================================

Another surface of UCS uses exactly four bytes per character, and is a mere dump of the internal memory representation which is natural for the whole charset and as such, conveys with it endianness problems.

Use it as a genuine charset.  This charset is available in recode under the name ISO-10646-UCS-4.  Accepted aliases are UCS, UCS-4, ISO_10646, 10646 and u4.

Universal Transformation Format, 7 bits
=======================================

UTF-7 comes from IETF rather than ISO, and is described by RFC 2152, in the MIME series.  The UTF-7 encoding is meant to fit UCS-2 over channels limited to seven bits per byte.  It proceeds from a mix between the spirit of Quoted-Printable and methods of Base64, adapted to Unicode contexts.

This charset is available in recode under the name UNICODE-1-1-UTF-7.  Accepted aliases are UTF-7, TF-7 and u7.

Universal Transformation Format, 8 bits
=======================================

Even if UTF-8 does not originally come from IETF, there is now RFC 2279 to describe it.  In letters sent on 1995-01-21 and 1995-04-20, Markus Kuhn writes:

     UTF-8 is an ASCII compatible multi-byte encoding of the ISO 10646 universal character set (UCS).  UCS is a 31-bit superset of all other character set standards.  The first 256 characters of UCS are identical to those of ISO 8859-1 (Latin-1).  The UCS-2 encoding of UCS is a sequence of bigendian 16-bit words, the UCS-4 encoding is a sequence of bigendian 32-bit words.  The UCS-2 subset of ISO 10646 is also known as ``Unicode''.  As both UCS-2 and UCS-4 require heavy modifications to traditional ASCII oriented system designs (e.g. Unix), the UTF-8 encoding has been designed for these applications.

     In UTF-8, only ASCII characters are encoded using bytes below 128.  All other non-ASCII characters are encoded as multi-byte sequences consisting only of bytes in the range 128-253.  This avoids critical bytes like NUL and / in UTF-8 strings, which makes the UTF-8 encoding suitable for being handled by the standard C string library and being used in Unix file names.  Other properties include the preserved lexical sorting order and that UTF-8 allows easy self-synchronisation of software receiving UTF-8 strings.

UTF-8 is the most common external surface of UCS, each character uses from one to six bytes, and is able to encode all 2^31 characters of the UCS.  It is implemented as a charset, with the following properties:

  * Strict 7-bit ASCII is completely invariant under UTF-8, and those are the only one-byte characters.  UCS values and ASCII values coincide.  No multi-byte characters ever contain bytes less than 128.  NUL is NUL.  A multi-byte character always starts with a byte of 192 or more, and is always followed by a number of bytes between 128 to 191.  That means that you may read at random on disk or memory, and easily discover the start of the current, next or previous character.  You can count, skip or extract characters with this only knowledge.

  * If you read the first byte of a multi-byte character in binary, it contains many 1 bits in successions starting with the most significant one (from the left), at least two.  The length of this 1 sequence equals the byte size of the character.  All succeeding bytes start by 10. This is a lot of redundancy, making it fairly easy to guess that a file is valid UTF-8, or to safely state that it is not.

  * In a multi-byte character, if you remove all leading 1 bits of the first byte of a multi-byte character, and the initial 10 bits of all remaining bytes (so keeping 6 bits per byte for those), the remaining bits concatenated are the UCS value.

These properties also have a few nice consequences:

  * Conversion to/from values is algorithmically simple, and reasonably speedy.

  * A sequence of N bytes can hold characters needing up to 2 + 5N bits in their UCS representation.  Here, N is a number between 1 and 6.  So, UTF-8 is most economical when mapping ASCII (1 byte), followed by UCS-2 (1 to 3 bytes) and UCS-4 (1 to 6 bytes).

  * The lexicographic sorting order of UCS strings is preserved.

  * Bytes with value 254 or 255 never appear, and because of that, these are sometimes used when escape mechanisms are needed.

In some case, when little processing is done on a lot of strings, one may choose for efficiency reasons to handle UTF-8 strings directly even if variable length, as it is easy to get start of characters.  Character insertion or replacement might require moving the remainder of the string in either direction.  In most cases, it is faster and easier to convert from UTF-8 to UCS-2 or UCS-4 prior to processing.

This charset is available in recode under the name UTF-8. Accepted aliases are UTF-2, UTF-FSS, FSS_UTF, TF-8 and u8.

Universal Transformation Format, 16 bits
========================================

Another external surface of UCS is also variable length, each character using either two or four bytes.  It is usable for the subset defined by the first million characters (17 * 2^16) of UCS.

Martin J. Dürst writes (to comp.std.internat, on 1995-03-28):

     UTF-16 is another method that reserves two times 1024 codepoints in Unicode and uses them to index around one million additional characters. UTF-16 is a little bit like former multibyte codes, but quite not so, as both the first and the second 16-bit code clearly show what they are.  The idea is that one million codepoints should be enough for all the rare Chinese ideograms and historical scripts that do not fit into the Base Multilingual Plane of ISO 10646 (with just about 63,000 positions available, now that 2,000 are gone).

This charset is available in recode under the name UTF-16. Accepted aliases are Unicode, TF-16 and u6.

Frequency count of characters
=============================

A device may be used to obtain a list of characters in a file, and how many times each character appears.  Each count is followed by the UCS-2 value of the character and, when known, the RFC 1345 mnemonic for that character.

This charset is available in recode under the name count-characters.

This count feature has been implemented as a charset.  This may change in some later version, as it would sometimes be convenient to count original bytes, instead of their UCS-2 equivalent.

Fully interpreted UCS dump
==========================

Another device may be used to get fully interpreted dumps of an UCS-2 stream of characters, with one UCS-2 character displayed on a full output line.  Each line receives the RFC 1345 mnemonic for the character if it exists, the UCS-2 value of the character, and a descriptive comment for that character.  As each input character produces its own output line, beware that the output file from this conversion may be much, much bigger than the input file.

This charset is available in recode under the name dump-with-names.

This dump-with-names feature has been implemented as a charset rather than a surface.  This is surely debatable.  The current implementation allows for dumping charsets other than UCS-2.  For example, the command recode l2..full < INPUT implies a necessary conversion from Latin-2 to UCS-2, as dump-with-names is only connected out from UCS-2.  In such cases, recode does not display the original Latin-2 codes in the dump, only the corresponding UCS-2 values.  To give a simpler example, the command

     echo 'Hello, world!' | recode us..dump

produces the following output:

     UCS2   Mne   Description

     0048   H     latin capital letter h
     0065   e     latin small letter e
     006C   l     latin small letter l
     006C   l     latin small letter l
     006F   o     latin small letter o
     002C   ,     comma
     0020   SP    space
     0077   w     latin small letter w
     006F   o     latin small letter o
     0072   r     latin small letter r
     006C   l     latin small letter l
     0064   d     latin small letter d
     0021   !     exclamation mark
     000A   LF    line feed (lf)

The descriptive comment is given in English and ASCII, yet if the English description is not available but a French one is, then the French description is given instead, using Latin-1.  However, if the LANGUAGE or LANG environment variable begins with the letters fr, then listing preference goes to French when both descriptions are available.

Here is another example.  To get the long description of the code 237 in Latin-5 table, one may use the following command.

     echo -n 237 | recode l5/d..dump

If your echo does not grok -n, use echo 237\c instead. Here is how to see what Unicode U+03C6 means, while getting rid of the title lines.

     echo -n 0x03C6 | recode u2/x2..dump | tail +3

The iconv library
*****************

The recode library itself contains most code and tables from the portable iconv library, written by Bruno Haible.  In fact, many capabilities of the recode library are duplicated because of this merging, as the older recode and iconv libraries share many charsets.  We discuss, here, the issues related to this duplication, and other peculiarities specific to the iconv library.  The plan is to remove duplications and better merge specificities, as recode evolves.

As implemented, if a recoding request can be satisfied by the recode library both with and without its iconv library part, it is likely that the iconv library will be used.  To sort out if the iconv is indeed used of not, just use the -v or --verbose option, see Recoding.

The :libiconv: charset represents a conceptual pivot charset within the iconv part of the recode library (in fact, this pivot exists, but is not directly reachable).  This charset has a mere : (a colon) for an alias.  It is not allowed to recode from or to this charset directly.  But when this charset is selected as an intermediate, usually by automatic means, then the iconv part of the recode library is called to handle the transformations. By using an --ignore=:libiconv: option on the recode call or equivalently, but more simply, -x:, recode is instructed to fully avoid this charset as an intermediate, with the consequence that the iconv part of the library is defeated.  Consider these two calls:

     recode l1..1250 < INPUT > OUTPUT
     recode -x: l1..1250 < INPUT > OUTPUT

Both should transform INPUT from ISO-8859-1 to CP1250 on OUTPUT.  The first call uses the iconv part of the library, while the second call avoids it.  Whatever the path used, the results should normally be identical.  However, there might be observable differences. Most of them might result from reversibility issues, as the iconv engine, which the recode library directly uses for the time being, does not address reversibility.  Even if much less likely, some differences might result from slight errors in the tables used, such differences should then be reported as bugs.

Other irregularities might be seen in the area of error detection and recovery.  The recode library usually tries to detect canonicity errors in input, and production of ambiguous output, but the iconv part of the library currently does not.  Input is always validated, however. The recode library may not always react properly when its iconv part has no translation for a given character.

Within a collection of names for a single charset, the recode library distinguishes one of them as being the genuine charset name, while the others are said to be aliases.  When recode lists all charsets, for example with the -l or --list option, the list integrates all iconv library charsets.  The selection of one of the aliases as the genuine charset name is an artifact added by recode, it does not come from iconv.  Moreover, the recode library dynamically resolves some conflicts when it initialises itself at runtime. This might explain some discrepancies in the table below, as for what is the genuine charset name.

     [file libiconv.texi not included]

Tabular sources (RFC 1345)
**************************

An important part of the tabular charset knowledge in recode comes from RFC 1345 or, alternatively, from the chset tools, both maintained by Keld Simonsen.  The RFC 1345 document:

     ``Character Mnemonics & Character Sets'', K. Simonsen, Request for Comments no. 1345, Network Working Group, June 1992.

defines many character mnemonics and character sets.  The recode library implements most of RFC 1345, however:

  * It does not recognise those charsets which overload character positions: dk-us and us-dk.  However, see Mixed.

  * It does not recognise those charsets which combine two characters for representing a third: ANSI_X3.110-1983, ISO_6937-2-add, T.101-G2, T.61-8bit, iso-ir-90 and videotex-suppl.

  * It does not recognise 16-bits charsets: GB_2312-80, JIS_C6226-1978, JIS_C6226-1983, JIS_X0212-1990 and KS_C_5601-1987.

  * It interprets the charset isoir91 as NATS-DANO (alias iso-ir-9-1), not as JIS_C6229-1984-a (alias iso-ir-91).  It also interprets the charset isoir92 as NATS-DANO-ADD (alias iso-ir-9-2), not as JIS_C6229-1984-b (alias iso-ir-92).  It might be better just avoiding these two alias names.

Keld Simonsen keld@dkuug.dk did most of RFC 1345 himself, with some funding from Danish Standards and Nordic standards (INSTA) project. He also did the character set design work, with substantial input from Olle Jaernefors.  Keld typed in almost all of the tables, some have been contributed.  A number of people have checked the tables in various ways.  The RFC lists a number of people who helped.

Keld and the recode maintainer have an arrangement by which any new discovered information submitted by recode users, about tabular charsets, is forwarded to Keld, eventually merged into Keld's work, and only then, reimported into recode.  Neither the recode program nor its library try to compete, nor even establish themselves as an alternate or diverging reference: RFC 1345 and its new drafts stay the genuine source for most tabular information conveyed by recode. Keld has been more than collaborative so far, so there is no reason that we act otherwise.  In a word, recode should be perceived as the application of external references, but not as a reference in itself.

Internally, RFC 1345 associates which each character an unambiguous mnemonic of a few characters, taken from ISO 646, which is a minimal ASCII subset of 83 characters.  The charset made up by these mnemonics is available in recode under the name RFC1345.  It has mnemonic and 1345 for aliases.  As implemened, this charset exactly corresponds to mnemonic+ascii+38, using RFC 1345 nomenclature.  Roughly said, ISO 646 characters represent themselves, except for the ampersand (&) which appears doubled.  A prefix of a single ampersand introduces a mnemonic.  For mnemonics using two characters, the prefix is immediately by the mnemonic.  For longer mnemonics, the prefix is followed by an underline (_), the mmemonic, and another underline. Conversions to this charset are usually reversible.

Currently, recode does not offer any of the many other possible variations of this family of representations.  They will likely be implemented in some future version, however.

          [file rfc1345.texi not included]

ASCII and some derivatives
**************************

Usual ASCII
===========

This charset is available in recode under the name ASCII. In fact, it's true name is ANSI_X3.4-1968 as per RFC 1345, accepted aliases being ANSI_X3.4-1986, ASCII, IBM367, ISO646-US, ISO_646.irv:1991, US-ASCII, cp367, iso-ir-6 and us.  The shortest way of specifying it in recode is us.

This documentation used to include ASCII tables.  They have been removed since the recode program can now recreate these easily:

     recode -lf us                   for commented ASCII
     recode -ld us                   for concise decimal table
     recode -lo us                   for concise octal table
     recode -lh us                   for concise hexadecimal table

ASCII extended by Latin Alphabets
=================================

There are many Latin charsets.  The following has been written by Tim Lasko lasko@video.dec.com, a long while ago:

     ISO Latin-1, or more completely ISO Latin Alphabet No 1, is now an international standard as of February 1987 (IS 8859, Part 1).  For those American USEnet'rs that care, the 8-bit ASCII standard, which is essentially the same code, is going through the final administrative processes prior to publication.  ISO Latin-1 (IS 8859/1) is actually one of an entire family of eight-bit one-byte character sets, all having ASCII on the left hand side, and with varying repertoires on the right hand side:

       * Latin Alphabet No 1 (caters to Western Europe - now approved).

       * Latin Alphabet No 2 (caters to Eastern Europe - now approved).

       * Latin Alphabet No 3 (caters to SE Europe + others - in draft ballot).

       * Latin Alphabet No 4 (caters to Northern Europe - in draft ballot).

       * Latin-Cyrillic alphabet (right half all Cyrillic - processing currently suspended pending USSR input).

       * Latin-Arabic alphabet (right half all Arabic - now approved).

       * Latin-Greek alphabet (right half Greek + symbols - in draft ballot).

       * Latin-Hebrew alphabet (right half Hebrew + symbols - proposed).

The ISO Latin Alphabet 1 is available as a charset in recode under the name Latin-1.  In fact, it's true name is ISO_8859-1:1987 as per RFC 1345, accepted aliases being CP819, IBM819, ISO-8859-1, ISO_8859-1, iso-ir-100, l1 and Latin-1.  The shortest way of specifying it in recode is l1.

It is an eight-bit code which coincides with ASCII for the lower half. This documentation used to include Latin-1 tables.  They have been removed since the recode program can now recreate these easily:

     recode -lf l1                   for commented ISO Latin-1
     recode -ld l1                   for concise decimal table
     recode -lo l1                   for concise octal table
     recode -lh l1                   for concise hexadecimal table

ASCII 7-bits, BS to overstrike
==============================

This charset is available in recode under the name ASCII-BS, with BS as an acceptable alias.

The file is straight ASCII, seven bits only.  According to the definition of ASCII, diacritics are applied by a sequence of three characters: the letter, one BS, the diacritic mark.  We deviate slightly from this by exchanging the diacritic mark and the letter so, on a screen device, the diacritic will disappear and let the letter alone.  At recognition time, both methods are acceptable.

The French quotes are coded by the sequences: < BS " or " BS < for the opening quote and > BS " or " BS > for the closing quote.  This artificial convention was inherited in straight ASCII-BS from habits around Bang-Bang entry, and is not well known.  But we decided to stick to it so that ASCII-BS charset will not lose French quotes.

The ASCII-BS charset is independent of ASCII, and different.  The following examples demonstrate this, knowing at advance that !2 is the Bang-Bang way of representing an e with an acute accent.  Compare:

     % echo \!2 | recode -v bang..l1/d
     Request: Bang-Bang..ISO-8859-1/Decimal-1
     233,  10

with:

     % echo \!2 | recode -v bang..bs/d
     Request: Bang-Bang..ISO-8859-1..ASCII-BS/Decimal-1
      39,   8, 101,  10

In the first case, the e with an acute accent is merely transmitted by the Latin-1..ASCII mapping, not having a special recoding rule for it.  In the Latin-1..ASCII-BS case, the acute accent is applied over the e with a backspace: diacriticised characters have special rules.  For the ASCII-BS charset, reversibility is still possible, but there might be difficult cases.

ASCII without diacritics nor underline
======================================

This charset is available in recode under the name flat.

This code is ASCII expunged of all diacritics and underlines, as long as they are applied using three character sequences, with BS in the middle.  Also, despite slightly unrelated, each control character is represented by a sequence of two or three graphic characters.  The newline character, however, keeps its functionality and is not represented.

Note that charset flat is a terminal charset.  We can convert to flat, but not from it.

Some IBM or Microsoft charsets
******************************

The recode program provides various IBM or Microsoft code pages (see Tabular).  An easy way to find them all at once out of the recode program itself is through the command:

     recode -l | egrep -i '(CP|IBM)[0-9]'

But also, see few special charsets presented in the incoming sections.

EBCDIC code
===========

This charset is the IBM's External Binary Coded Decimal for Interchange Coding.  This is an eight bits code.  The following three variants were implemented in recode independently of RFC 1345:

EBCDIC
     In recode, the us..ebcdic conversion is identical to dd conv=ebcdic conversion, and recode ebcdic..us conversion is identical to dd conv=ascii conversion.  This charset also represents the way Control Data Corporation relates EBCDIC to 8-bits ASCII.

EBCDIC-CCC
     In recode, the us..ebcdic-ccc or ebcdic-ccc..us conversions represent the way Concurrent Computer Corporation (formerly Perkin Elmer) relates EBCDIC to 8-bits ASCII.

EBCDIC-IBM
     In recode, the us..ebcdic-ibm conversion is almost identical to the GNU dd conv=ibm conversion.  Given the exact dd conv=ibm conversion table, recode once said:

          Codes  91 and 213 both recode to 173
          Codes  93 and 229 both recode to 189
          No character recodes to  74
          No character recodes to 106

     So I arbitrarily chose to recode 213 by 74 and 229 by 106.  This makes the EBCDIC-IBM recoding reversible, but this is not necessarily the best correction.  In any case, I think that GNU dd should be amended. dd and recode should ideally agree on the same correction. So, this table might change once again.

RFC 1345 brings into recode 15 other EBCDIC charsets, and 21 other charsets having EBCDIC in at least one of their alias names.  You can get a list of all these by executing:

     recode -l | grep -i ebcdic

Note that recode may convert a pure stream of EBCDIC characters, but it does not know how to handle binary data between records which is sometimes used to delimit them and build physical blocks.  If end of lines are not marked, fixed record size may produce something readable, but VB or VBS blocking is likely to yield some garbage in the converted results.

IBM's PC code
=============

This charset is available in recode under the name IBM-PC, with dos, MSDOS and pc as acceptable aliases. The shortest way of specifying it in recode is pc.

The charset is aimed towards a PC microcomputer from IBM or any compatible. This is an eight-bit code.  This charset is fairly old in recode, its tables were produced a long while ago by mere inspection of a printed chart of the IBM-PC codes and glyph.

It has CR-LF as its implied surface.  This means that, if the original end of lines have to be preserved while going out of IBM-PC, they should currently be added back through the usage of a surface on the other charset, or better, just never removed.  Here are examples for both cases:

     recode pc..l2/cl < INPUT > OUTPUT
     recode pc/..l2 < INPUT > OUTPUT

RFC 1345 brings into recode 44 IBM charsets or code pages, and also 8 other code pages.  You can get a list of these all these by executing: (On DOS/Windows, stock shells do not know that apostrophes quote special characters like |, so one need to use double quotes instead of apostrophes.)

     recode -l | egrep -i '(CP|IBM)[0-9]'

All charset or aliases beginning with letters CP or IBM also have CR-LF as their implied surface.  The same is true for a purely numeric alias in the same family.  For example, all of 819, CP819 and IBM819 imply CR-LF as a surface.  Note that ISO-8859-1 does not imply a surface, despite it shares the same tabular data as 819.

There are a few discrepancies between this IBM-PC charset and the very similar RFC 1345 charset ibm437, which have not been analysed yet, so the charsets are being kept separate for now.  This might change in the future, and the IBM-PC charset might disappear.  Wizards would be interested in comparing the output of these two commands:

     recode -vh IBM-PC..Latin-1
     recode -vh IBM437..Latin-1

The first command uses the charset prior to RFC 1345 introduction. Both methods give different recodings.  These differences are annoying, the fuzziness will have to be explained and settle down one day.

Unisys' Icon code
=================

This charset is available in recode under the name Icon-QNX, with QNX as an acceptable alias.

The file is using Unisys' Icon way to represent diacritics with code 25 escape sequences, under the system QNX.  This is a seven-bit code, even if eight-bit codes can flow through as part of IBM-PC charset.

Charsets for CDC machines
*************************

What is now recode evolved out, through many transformations really, from a set of programs which were originally written in COMPASS, Control Data Corporation's assembler, with bits in FORTRAN, and later rewritten in CDC 6000 Pascal.  The CDC heritage shows by the fact some old CDC charsets are still supported.

The recode author used to be familiar with CDC Scope-NOS/BE and Kronos-NOS, and many CDC formats.  Reading CDC tapes directly on other machines is often a challenge, and recode does not always solve it.  It helps having tapes created in coded mode instead of binary mode, and using S (Stranger) tapes instead of I (Internal) tapes. ANSI labels and multi-file tapes might be the source of trouble.  There are ways to handle a few Cyber Record Manager formats, but some of them might be quite difficult to decode properly after the transfer is done.

The recode program is usable only for a small subset of NOS text formats, and surely not with binary textual formats, like UPDATE or MODIFY sources, for example.  recode is not especially suited for reading 8/12 or 56/60 packing, yet this could easily arranged if there was a demand for it.  It does not have the ability to translate Display Code directly, as the ASCII conversion implied by tape drivers or FTP does the initial approximation.  recode can decode 6/12 caret notation over Display Code already mapped to ASCII.

Control Data's Display Code
===========================

This code is not available in recode, but repeated here for reference.  This is a 6-bit code used on CDC mainframes.

     Octal display code to graphic       Octal display code to octal ASCII

     00  :    20  P    40  5   60  #     00 072  20 120  40 065  60 043
     01  A    21  Q    41  6   61  [     01 101  21 121  41 066  61 133
     02  B    22  R    42  7   62  ]     02 102  22 122  42 067  62 135
     03  C    23  S    43  8   63  %     03 103  23 123  43 070  63 045
     04  D    24  T    44  9   64  "     04 104  24 124  44 071  64 042
     05  E    25  U    45  +   65  _     05 105  25 125  45 053  65 137
     06  F    26  V    46  -   66  !     06 106  26 126  46 055  66 041
     07  G    27  W    47  *   67  &     07 107  27 127  47 052  67 046
     10  H    30  X    50  /   70  '     10 110  30 130  50 057  70 047
     11  I    31  Y    51  (   71  ?     11 111  31 131  51 050  71 077
     12  J    32  Z    52  )   72  <     12 112  32 132  52 051  72 074
     13  K    33  0    53  $   73  >     13 113  33 060  53 044  73 076
     14  L    34  1    54  =   74  @     14 114  34 061  54 075  74 100
     15  M    35  2    55      75  \     15 115  35 062  55 040  75 134
     16  N    36  3    56  ,   76  ^     16 116  36 063  56 054  76 136
     17  O    37  4    57  .   77  ;     17 117  37 064  57 056  77 073

In older times, : used octal 63, and octal 0 was not a character. The table above shows the ASCII glyph interpretation of codes 60 to 77, yet these 16 codes were once defined differently.

There is no explicit end of line in Display Code, and the Cyber Record Manager introduced many new ways to represent them, the traditional end of lines being reachable by setting RT to Z.  If 6-bit bytes in a file are sequentially counted from 1, a traditional end of line does exist if bytes 10*N+9 and 10N+10 are both zero for a given N, in which case these two bytes are not to be interpreted as ::.  Also, up to 9 immediately preceeding zero bytes, going backward, are to be considered as part of the end of line and not interpreted as : (This convention replaced an older one saying that up to 4 immediately preceeding pairs of zero bytes, going backward, are to be considered as part of the end of line and not interpreted as ::.).

ASCII 6/12 from NOS
===================

This charset is available in recode under the name CDC-NOS, with NOS as an acceptable alias.

This is one of the charsets in use on CDC Cyber NOS systems to represent ASCII, sometimes named NOS 6/12 code for coding ASCII.  This code is also known as caret ASCII.  It is based on a six bits character set in which small letters and control characters are coded using a ^ escape and, sometimes, a @ escape.

The routines given here presume that the six bits code is already expressed in ASCII by the communication channel, with embedded ASCII ^ and @ escapes.

Here is a table showing which characters are being used to encode each ASCII character.

     000  ^5  020  ^#  040     060  0  100 @A  120  P  140  @G  160  ^P
     001  ^6  021  ^[  041  !  061  1  101  A  121  Q  141  ^A  161  ^Q
     002  ^7  022  ^]  042  "  062  2  102  B  122  R  142  ^B  162  ^R
     003  ^8  023  ^%  043  #  063  3  103  C  123  S  143  ^C  163  ^S
     004  ^9  024  ^"  044  $  064  4  104  D  124  T  144  ^D  164  ^T
     005  ^+  025  ^_  045  %  065  5  105  E  125  U  145  ^E  165  ^U
     006  ^-  026  ^!  046  &  066  6  106  F  126  V  146  ^F  166  ^V
     007  ^*  027  ^&  047  '  067  7  107  G  127  W  147  ^G  167  ^W
     010  ^/  030  ^'  050  (  070  8  110  H  130  X  150  ^H  170  ^X
     011  ^(  031  ^?  051  )  071  9  111  I  131  Y  151  ^I  171  ^Y
     012  ^)  032  ^<  052  *  072 @D  112  J  132  Z  152  ^J  172  ^Z
     013  ^$  033  ^>  053  +  073  ;  113  K  133  [  153  ^K  173  ^0
     014  ^=  034  ^@  054  ,  074  <  114  L  134  \  154  ^L  174  ^1
     015  ^   035  ^\  055  -  075  =  115  M  135  ]  155  ^M  175  ^2
     016  ^,  036  ^^  056  .  076  >  116  N  136 @B  156  ^N  176  ^3
     017  ^.  037  ^;  057  /  077  ?  117  O  137  _  157  ^O  177  ^4

ASCII ``bang bang''
===================

This charset is available in recode under the name Bang-Bang.

This code, in use on Cybers at Université de Montréal mainly, served to code a lot of French texts.  The original name of this charset is ASCII codé Display.  This code is also known as Bang-bang. It is based on a six bits character set in which capitals, French diacritics and a few others are coded using an ! escape followed by a single character, and control characters using a double ! escape followed by a single character.

The routines given here presume that the six bits code is already expressed in ASCII by the communication channel, with embedded ASCII ! escapes.

Here is a table showing which characters are being used to encode each ASCII character.

     000 !!@  020 !!P  040    060 0  100 @   120 !P  140 !@ 160 P
     001 !!A  021 !!Q  041 !" 061 1  101 !A  121 !Q  141 A  161 Q
     002 !!B  022 !!R  042 "  062 2  102 !B  122 !R  142 B  162 R
     003 !!C  023 !!S  043 #  063 3  103 !C  123 !S  143 C  163 S
     004 !!D  024 !!T  044 $  064 4  104 !D  124 !T  144 D  164 T
     005 !!E  025 !!U  045 %  065 5  105 !E  125 !U  145 E  165 U
     006 !!F  026 !!V  046 &  066 6  106 !F  126 !V  146 F  166 V
     007 !!G  027 !!W  047 '  067 7  107 !G  127 !W  147 G  167 W
     010 !!H  030 !!X  050 (  070 8  110 !H  130 !X  150 H  170 X
     011 !!I  031 !!Y  051 )  071 9  111 !I  131 !Y  151 I  171 Y
     012 !!J  032 !!Z  052 *  072 :  112 !J  132 !Z  152 J  172 Z
     013 !!K  033 !![  053 +  073 ;  113 !K  133 [   153 K  173 ![
     014 !!L  034 !!\  054 ,  074 <  114 !L  134 \   154 L  174 !\
     015 !!M  035 !!]  055 -  075 =  115 !M  135 ]   155 M  175 !]
     016 !!N  036 !!^  056 .  076 >  116 !N  136 ^   156 N  176 !^
     017 !!O  037 !!_  057 /  077 ?  117 !O  137 _   157 O  177 !_

Other micro-computer charsets
*****************************

The NeXT charset, which used to be especially provided in releases of recode before 3.5, has been integrated since as one RFC 1345 table.

Apple's Macintosh code
======================

This charset is available in recode under the name Apple-Mac. The shortest way of specifying it in recode is ap.

The charset is aimed towards a Macintosh micro-computer from Apple. This is an eight bit code.  The file is the data fork only.  This charset is fairly old in recode, its tables were produced a long while ago by mere inspection of a printed chart of the Macintosh codes and glyph.

It has CR as its implied surface.  This means that, if the original end of lines have to be preserved while going out of Apple-Mac, they should currently be added back through the usage of a surface on the other charset, or better, just never removed.  Here are examples for both cases:

     recode ap..l2/cr < INPUT > OUTPUT
     recode ap/..l2 < INPUT > OUTPUT

RFC 1345 brings into recode 2 other Macintosh charsets.  You can discover them by using grep over the output of recode -l:

     recode -l | grep -i mac

Charsets macintosh and macintosh_ce, as well as their aliases mac and macce also have CR as their implied surface.

There are a few discrepancies between the Apple-Mac charset and the very similar RFC 1345 charset macintosh, which have not been analysed yet, so the charsets are being kept separate for now.  This might change in the future, and the Apple-Mac charset might disappear. Wizards would be interested in comparing the output of these two commands:

     recode -vh Apple-Mac..Latin-1
     recode -vh macintosh..Latin-1

The first command use the charset prior to RFC 1345 introduction. Both methods give different recodings.  These differences are annoying, the fuzziness will have to be explained and settle down one day.

As a side note, some people ask if there is a Macintosh port of the recode program.  I'm not aware of any.  I presume that if the tool fills a need for Macintosh users, someone will port it one of these days?

Atari ST code
=============

This charset is available in recode under the name AtariST.

This is the character set used on the Atari ST/TT/Falcon.  This is similar to IBM-PC, but differs in some details: it includes some more accented characters, the graphic characters are mostly replaced by Hebrew characters, and there is a true German sharp s different from Greek beta.

About the end-of-line conversions: the canonical end-of-line on the Atari is \r\n, but unlike IBM-PC, the OS makes no difference between text and binary input/output; it is up to the application how to interpret the data.  In fact, most of the libraries that come with compilers can grok both \r\n and \n as end of lines.  Many of the users who also have access to Unix systems prefer \n to ease porting Unix utilities.  So, for easing reversibility, recode tries to let \r undisturbed through recodings.

Various other charsets
**********************

Even if these charsets were originally added to recode for handling texts written in French, they find other uses.  We did use them a lot for writing French diacriticised texts in the past, so recode knows how to handle these particularly well for French texts.

World Wide Web representations
==============================

Character entities have been introduced by SGML and made widely popular through HTML, the markup language in use for the World Wide Web, or Web or WWW for short.  For representing unusual characters, HTML texts use special sequences, beginning with an ampersand & and ending with a semicolon ;.  The sequence may itself start with a number sigh # and be followed by digits, so forming a numeric character reference, or else be an alphabetic identifier, so forming a character entity reference.

The HTML standards have been revised into different HTML levels over time, and the list of allowable character entities differ in them.  The later XML, meant to simplify many things, has an option (standalone=yes) which much restricts that list.  The recode library is able to convert character references between their mnemonic form and their numeric form, depending on aimed HTML standard level.  It also can, of course, convert between HTML and various other charsets.

Here is a list of those HTML variants which recode supports. Some notes have been provided by Francois Yergeau yergeau@alis.com.

XML-standalone
     This charset is available in recode under the name XML-standalone, with h0 as an acceptable alias.  It is documented in section 4.1 of http://www.w3.org/TR/REC-xml. It only knows &amp;, &gt;, &lt;, &quot; and &apos;.

HTML_1.1
     This charset is available in recode under the name HTML_1.1, with h1 as an acceptable alias.  HTML 1.0 was never really documented.

HTML_2.0
     This charset is available in recode under the name HTML_2.0, and has RFC1866, 1866 and h2 for aliases.  HTML 2.0 entities are listed in RFC 1866.  Basically, there is an entity for each alphabetical character in the right part of ISO 8859-1. In addition, there are four entities for syntax-significant ASCII characters: &amp;, &gt;, &lt; and &quot;.

HTML-i18n
     This charset is available in recode under the name HTML-i18n, and has RFC2070 and 2070 for aliases.  RFC 2070 added entities to cover the whole right part of ISO 8859-1.  The list is conveniently accessible at http://www.alis.com:8085/ietf/html/html-latin1.sgml.  In addition, four i18n-related entities were added: &zwnj; (&#8204;), &zwj; (&#8205;), &lrm; (&#8206) and &rlm; (&#8207;).

HTML_3.2
     This charset is available in recode under the name HTML_3.2, with h3 as an acceptable alias. HTML 3.2 (http://www.w3.org/TR/REC-html32.html) took up the full Latin-1 list but not the i18n-related entities from RFC 2070.

HTML_4.0
     This charset is available in recode under the name HTML_4.0, and has h4 and h for aliases.  Beware that the particular alias h is not tied to HTML 4.0, but to the highest HTML level supported by recode; so it might later represent HTML level 5 if this is ever created.  HTML 4.0 (http://www.w3.org/TR/REC-html40/) has the whole Latin-1 list, a set of entities for symbols, mathematical symbols, and Greek letters, and another set for markup-significant and internationalization characters comprising the 4 ASCII entities, the 4 i18n-related from RFC 2070 plus some more. See http://www.w3.org/TR/REC-html40/sgml/entities.html.

Printable characters from Latin-1 may be used directly in an HTML text. However, partly because people have deficient keyboards, partly because people want to transmit HTML texts over non 8-bit clean channels while not using MIME, it is common (yet debatable) to use character entity references even for Latin-1 characters, when they fall outside ASCII (that is, when they have the 8th bit set).

When you recode from another charset to HTML, beware that all occurrences of double quotes, ampersands, and left or right angle brackets are translated into special sequences.  However, in practice, people often use ampersands and angle brackets in the other charset for introducing HTML commands, compromising it: it is not pure HTML, not it is pure other charset.  These particular translations can be rather inconvenient, they may be specifically inhibited through the command option -d (see Mixed).

Codes not having a mnemonic entity are output by recode using the &#NNN; notation, where NNN is a decimal representation of the UCS code value.  When there is an entity name for a character, it is always preferred over a numeric character reference.  ASCII printable characters are always generated directly.  So is the newline.  While reading HTML, recode supports numeric character reference as alternate writings, even when written as hexadecimal numbers, as in &#xfffd. This is documented in:

     http://www.w3.org/TR/REC-html40/intro/sgmltut.html#h-3.2.3

When recode translates to HTML, the translation occurs according to the HTML level as selected by the goal charset.  When translating from HTML, recode not only accepts the character entity references known at that level, but also those of all other levels, as well as a few alternative special sequences, to be forgiving to files using other HTML standards.

The recode program can be used to normalise an HTML file using oldish conventions.  For example, it accepts &AE;, as this once was a valid writing, somewhere.  However, it should always produce &AElig; instead of &AE;.  Yet, this is not completely true.  If one does:

     recode h3..h3 < INPUT

the operation will be optimised into a mere copy, and you can get &AE; this way, if you had some in your input file.  But if you explicitly defeat the optimisation, like this maybe:

     recode h3..u2,u2..h3 < INPUT

then &AE; should be normalised into &AElig; by the operation.

LaTeX macro calls
=================

This charset is available in recode under the name LaTeX and has ltex as an alias.  It is used for ASCII files coded to be read by LaTeX or, in certain cases, by TeX.

Whenever you recode from another charset to LaTeX, beware that all occurrences of backslashes \ are translated into the string \backslash{}.  However, in practice, people often use backslashes in the other charset for introducing TeX commands, compromising it: it is not pure TeX, nor it is pure other charset.  This translation of backslashes into \backslash{} can be rather inconvenient, it may be inhibited through the command option -d (see Mixed).

GNU project documentation files
===============================

This charset is available in recode under the name Texinfo and has texi and ti for aliases.  It is used by the GNU project for its documentation.  Texinfo files may be converted into Info files by the makeinfo program and into nice printed manuals by the TeX system.

Even if recode may transform other charsets to Texinfo, it may not read Texinfo files yet.  In these times, usages are also changing between versions of Texinfo, and recode only partially succeeds in correctly following these changes.  So, for now, Texinfo support in recode should be considered as work still in progress (!).

Vietnamese charsets
===================

We are currently experimenting the implementation, in recode, of a few character sets and transliterated forms to handle the Vietnamese language. They are quite briefly summarised, here.

TCVN
     The TCVN charset has an incomplete name.  It might be one of the three charset VN1, VN2 or VN3.  Yes VN2 might be a second version of VISCII.  To be clarified.

VISCII
     This is an 8-bit character set which seems to be rather popular for writing Vietnamese.

VPS
     This is an 8-bit character set for Vietnamese.  No much reference.

VIQR
     The VIQR convention is a 7-bit, ASCII transliteration for Vietnamese.

VNI
     The VNI convention is a 8-bit, Latin-1 transliteration for Vietnamese.

Still lacking for Vietnamese in recode, are the charsets CP1129 and CP1258.

African charsets
================

Some African character sets are available for a few languages, when these are heavily used in countries where French is also currently spoken.

One African charset is usable for Bambara, Ewondo and Fulfude, as well as for French.  This charset is available in recode under the name AFRFUL-102-BPI_OCIL.  Accepted aliases are bambara, bra, ewondo and fulfude.  Transliterated forms of the same are available under the name AFRFUL-103-BPI_OCIL.  Accepted aliases are t-bambara, t-bra, t-ewondo and t-fulfude.

Another African charset is usable for Lingala, Sango and Wolof, as well as for French.  This charset is available in recode under the name AFRLIN-104-BPI_OCIL.  Accepted aliases are lingala, lin, sango and wolof.  Transliterated forms of the same are available under the name AFRLIN-105-BPI_OCIL.  Accepted aliases are t-lingala, t-lin, t-sango and t-wolof.

To ease exchange with ISO-8859-1, there is a charset conveying transliterated forms for Latin-1 in a way which is compatible with the other African charsets in this series.  This charset is available in recode under the name AFRL1-101-BPI_OCIL.  Accepted aliases are t-fra and t-francais.

Cyrillic and other charsets
===========================

The following Cyrillic charsets are already available in recode through RFC 1345 tables: CP1251 with aliases 1251, ms-cyrl and windows-1251; CSN_369103 with aliases ISO-IR-139 and KOI8_L2; ECMA-cyrillic with aliases ECMA-113, ECMA-113:1986 and iso-ir-111, IBM880 with aliases 880, CP880 and EBCDIC-Cyrillic; INIS-cyrillic with alias iso-ir-51; ISO-8859-5 with aliases cyrillic,  ISO-8859-5:1988 and iso-ir-144; KOI-7; KOI-8 with alias GOST_19768-74; KOI8-R; KOI8-RU and finally KOI8-U.

There seems to remain some confusion in Roman charsets for Cyrillic languages, and because a few users requested it repeatedly, recode now offers special services in that area.  Consider these charsets as experimental and debatable, as the extraneous tables describing them are still a bit fuzzy or non-standard.  Hopefully, in the long run, these charsets will be covered in Keld Simonsen's works to the satisfaction of everybody, and this section will merely disappear.

KEYBCS2
     This charset is available under the name KEYBCS2, with Kamenicky as an accepted alias.

CORK
     This charset is available under the name CORK, with T1 as an accepted alias.

KOI-8_CS2
     This charset is available under the name KOI-8_CS2.

Easy French conventions
=======================

This charset is available in recode under the name Texte and has txte for an alias.  It is a seven bits code, identical to ASCII-BS, save for French diacritics which are noted using a slightly different convention.

At text entry time, these conventions provide a little speed up.  At read time, they slightly improve the readability over a few alternate ways of coding diacritics.  Of course, it would better to have a specialised keyboard to make direct eight bits entries and fonts for immediately displaying eight bit ISO Latin-1 characters.  But not everybody is so fortunate.  In a few mailing environments, and sadly enough, it still happens that the eight bit is often willing-fully destroyed.

Easy French has been in use in France for a while.  I only slightly adapted it (the diaeresis option) to make it more comfortable to several usages in Québec originating from Université de Montréal.  In fact, the main problem for me was not to necessarily to invent Easy French, but to recognise the ``best'' convention to use, (best is not being defined, here) and to try to solve the main pitfalls associated with the selected convention.  Shortly said, we have:

e'
     for e (and some other vowels) with an acute accent,

e`
     for e (and some other vowels) with a grave accent,

e^
     for e (and some other vowels) with a circumflex accent,

e"
     for e (and some other vowels) with a diaeresis,

c,
     for c with a cedilla.

There is no attempt at expressing the ae and oe diphthongs. French also uses tildes over n and a, but seldomly, and this is not represented either.  In some countries, : is used instead of " to mark diaeresis.  recode supports only one convention per call, depending on the -c option of the recode command. French quotes (sometimes called ``angle quotes'') are noted the same way English quotes are noted in TeX, id est by `` and ''. No effort has been put to preserve Latin ligatures (æ, œ) which are representable in several other charsets.  So, these ligatures may be lost through Easy French conventions.

The convention is prone to losing information, because the diacritic meaning overloads some characters that already have other uses.  To alleviate this, some knowledge of the French language is boosted into the recognition routines.  So, the following subtleties are systematically obeyed by the various recognisers.

 1. A comma which follows a c is interpreted as a cedilla only if it is followed by one of the vowels a, o or u.

 2. A single quote which follows a e does not necessarily means an acute accent if it is followed by a single other one.  For example:

     e'
          will give an e with an acute accent.

     e''
          will give a simple e, with a closing quotation mark.

     e'''
          will give an e with an acute accent, followed by a closing quotation mark.

     There is a problem induced by this convention if there are English quotations with a French text.  In sentences like:

          There's a meeting at Archie's restaurant.

     the single quotes will be mistaken twice for acute accents.  So English contractions and suffix possessives could be mangled.

 3. A double quote or colon, depending on -c option, which follows a vowel is interpreted as diaeresis only if it is followed by another letter. But there are in French several words that end with a diaeresis, and the recode library is aware of them.  There are words ending in ``igue'', either feminine words without a relative masculine (besaiguë and ciguë), or feminine words with a relative masculine (There are supposed to be seven words in this case.  So, one is missing.) (aiguë, ambiguë, contiguë, exiguë, subaiguë and suraiguë). There are also words not ending in ``igue'', but instead, either ending by
     ``i'' (Look at one of the following sentences (the second has to
     be interpreted with the -c option):)

          "Ai"e!  Voici le proble`me que j'ai"
          Ai:e!  Voici le proble`me que j'ai:

     There is an ambiguity between an ai", the small animal, and the indicative future of avoir (first person singular), when followed by what could be a diaeresis mark.  Hopefully, the case is solved by the fact that an apostrophe always precedes the verb and almost never the animal. (ai", congai", goi", hai"kai", inoui", sai", samurai", thai" and tokai"), ending by ``e'' (canoë) or ending by ``u'' (I did not pay attention to proper nouns, but this one showed up as being fairly evident.) (Esaü).

     Just to complete this topic, note that it would be wrong to make a rule for all words ending in ``igue'' as needing a diaerisis, as there are counter-examples (becfigue, bèsigue, bigue, bordigue, bourdigue, brigue, contre-digue, digue, d'intrigue, fatigue, figue, garrigue, gigue, igue, intrigue, ligue, prodigue, sarigue and zigue).

Mule as a multiplexed charset
=============================

This version of recode barely starts supporting multiplexed or super-charsets, that is, those encoding methods by which a single text stream may contain a combination of more than one constituent charset. The only multiplexed charset in recode is Mule, and even then, it is only very partially implemented: the only correspondence available is with Latin-1.  The author fastly implemented this only because he needed this for himself.  However, it is intended that Mule support to become more real in subsequent releases of recode.

Multiplexed charsets are not to be confused with mixed charset texts (see Mixed).  For mixed charset input, the rules allowing to distinguish which charset is current, at any given place, are kind of informal, and driven from the semantics of what the file contains.  On the other side, multiplexed charsets are designed to be interpreted fairly precisely, and quite independently of any informational context.

The spelling Mule originally stands for multilingual enhancement to GNU Emacs, it is the result of a collective effort orchestrated by Handa Ken'ichi since 1993.  When Mule got rewritten in the main development stream of GNU Emacs 20, the FSF renamed it MULE, meaning multilingual environment in GNU Emacs.  Even if the charset Mule is meant to stay internal to GNU Emacs, it sometimes breaks loose in external files, and as a consequence, a recoding tool is sometimes needed.  Within Emacs, Mule comes with Leim, which stands for libraries of emacs input methods.  One of these libraries is named quail (Usually, quail means quail egg in Japanese, while egg alone is usually chicken egg.  Both quail egg and chicken egg are popular food in Japan.  The quail input system has been named because it is smaller that the previous EGG system. As for EGG, it is the translation of TAMAGO.  This word comes from the Japanese sentence takusan matasete gomennasai, meaning sorry to have let you wait so long. Of course, the publication of EGG has been delayed many times... (Story by Takahashi Naoto)).

All about surfaces
******************

The trivial surface consists of using a fixed number of bits (often eight) for each character, the bits together hold the integer value of the index for the character in its charset table.  There are many kinds of surfaces, beyond the trivial one, all having the purpose of increasing selected qualities for the storage or transmission. For example, surfaces might increase the resistance to channel limits (Base64), the transmission speed (gzip), the information privacy (DES), the conformance to operating system conventions (CR-LF), the blocking into records (VB), and surely other things as well (These are mere examples to explain the concept, recode only has Base64 and CR-LF, actually.). Many surfaces may be applied to a stream of characters from a charset, the order of application of surfaces is important, and surfaces should be removed in the reverse order of their application.

Even if surfaces may generally be applied to various charsets, some surfaces were specifically designed for a particular charset, and would not make much sense if applied to other charsets.  In such cases, these conceptual surfaces have been implemented as recode charsets, instead of as surfaces.  This choice yields to cleaner syntax and usage.  See Universal.

Surfaces are implemented within recode as special charsets which may only transform to or from the data or tree special charsets.  Clever users may use this knowledge for writing surface names in requests exactly as if they were pure charsets, when the only need is to change surfaces without any kind of recoding between real charsets.  In such contexts, either data or tree may also be used as if it were some kind of generic, anonymous charset: the request data..SURFACE merely adds the given SURFACE, while the request SURFACE..data removes it.

The recode library distinguishes between mere data surfaces, and structural surfaces, also called tree surfaces for short.  Structural surfaces might allow, in the long run, transformations between a few specialised representations of structural information like MIME parts, Perl or Python initialisers, LISP S-expressions, XML, Emacs outlines, etc.

We are still experimenting with surfaces in recode.  The concept opens the doors to many avenues; it is not clear yet which ones are worth pursuing, and which should be abandoned.  In particular, implementation of structural surfaces is barely starting, there is not even a commitment that tree surfaces will stay in recode, if they do prove to be more cumbersome than useful.  This chapter presents all surfaces currently available.

Permuting groups of bytes
=========================

A permutation is a surface transformation which reorders groups of eight-bit bytes.  A 21 permutation exchanges pairs of successive bytes.  If the text contains an odd number of bytes, the last byte is merely copied.  An 4321 permutation inverts the order of quadruples of bytes.  If the text does not contains a multiple of four bytes, the remaining bytes are nevertheless permuted as 321 if there are three bytes, 21 if there are two bytes, or merely copied otherwise.

21
     This surface is available in recode under the name 21-Permutation and has swabytes for an alias.

4321
     This surface is available in recode under the name 4321-Permutation.

Representation for end of lines
===============================

The same charset might slightly differ, from one system to another, for the single fact that end of lines are not represented identically on all systems.  The representation for an end of line within recode is the ASCII or UCS code with value 10, or LF.  Other conventions for representing end of lines are available through surfaces.

CR
     This convention is popular on Apple's Macintosh machines.  When this surface is applied, each line is terminated by CR, which has ASCII value 13.  Unless the library is operating in strict mode, adding or removing the surface will in fact exchange CR and LF, for better reversibility.  However, in strict mode, the exchange does not happen, any CR will be copied verbatim while applying the surface, and any LF will be copied verbatim while removing it.

     This surface is available in recode under the name CR, it does not have any aliases.  This is the implied surface for the Apple Macintosh related charsets.

CR-LF
     This convention is popular on Microsoft systems running on IBM PCs and compatible.  When this surface is applied, each line is terminated by a sequence of two characters: one CR followed by one LF, in that order.

     For compatibility with oldish MS-DOS systems, removing a CR-LF surface will discard the first encountered C-z, which has ASCII value 26, and everything following it in the text. Adding this surface will not, however, append a C-z to the result.

     This surface is available in recode under the name CR-LF and has cl for an alias.  This is the implied surface for the IBM or Microsoft related charsets or code pages.

Some other charsets might have their own representation for an end of line, which is different from LF.  For example, this is the case of various EBCDIC charsets, or Icon-QNX.  The recoding of end of lines is intimately tied into such charsets, it is not available separately as surfaces.

MIME contents encodings
=======================

RFC 2045 defines two 7-bit surfaces, meant to prepare 8-bit messages for transmission.  Base64 is especially usable for binary entities, while Quoted-Printable is especially usable for text entities, in those case the lower 128 characters of the underlying charset coincide with ASCII.

Base64
     This surface is available in recode under the name Base64, with b64 and 64 as acceptable aliases.

Quoted-Printable
     This surface is available in recode under the name Quoted-Printable, with quote-printable and QP as acceptable aliases.

Note that UTF-7, which may be also considered as a MIME surface, is provided as a genuine charset instead, as it necessary relates to UCS-2 and nothing else.  See UTF-7.

A little historical note, also showing the three levels of acceptance of Internet standards.  MIME changed from a ``Proposed Standard'' (RFC 1341--1344, 1992) to a ``Draft Standard'' (RFC 1521--1523) in 1993, and was recycled as a ``Draft Standard'' in 1996-11.  It is not yet a ``Full Standard''.

Interpreted character dumps
===========================

Dumps are surfaces meant to express, in ways which are a bit more readable, the bit patterns used to represent characters.  They allow the inspection or debugging of character streams, but also, they may assist a bit the production of C source code which, once compiled, would hold in memory a copy of the original coding.  However, recode does not attempt, in any way, to produce complete C source files in dumps.  User hand editing or Makefile trickery is still needed for adding missing lines. Dumps may be given in decimal, hexadecimal and octal, and be based over chunks of either one, two or four eight-bit bytes.  Formatting has been chosen to respect the C language syntax for number constants, with commas and newlines inserted appropriately.

However, when dumping two or four byte chunks, the last chunk may be incomplete.  This is observable through the usage of narrower expression for that last chunk only.  Such a shorter chunk would not be compiled properly within a C initialiser, as all members of an array share a single type, and so, have identical sizes.

Octal-1
     This surface corresponds to an octal expression of each input byte.

     It is available in recode under the name Octal-1, with o1 and o as acceptable aliases.

Octal-2
     This surface corresponds to an octal expression of each pair of input bytes, except for the last pair, which may be short.

     It is available in recode under the name Octal-2 and has o2 for an alias.

Octal-4
     This surface corresponds to an octal expression of each quadruple of input bytes, except for the last quadruple, which may be short.

     It is available in recode under the name Octal-4 and has o4 for an alias.

Decimal-1
     This surface corresponds to an decimal expression of each input byte.

     It is available in recode under the name Decimal-1, with d1 and d as acceptable aliases.

Decimal-2
     This surface corresponds to an decimal expression of each pair of input bytes, except for the last pair, which may be short.

     It is available in recode under the name Decimal-2 and has d2 for an alias.

Decimal-4
     This surface corresponds to an decimal expression of each quadruple of input bytes, except for the last quadruple, which may be short.

     It is available in recode under the name Decimal-4 and has d4 for an alias.

Hexadecimal-1
     This surface corresponds to an hexadecimal expression of each input byte.

     It is available in recode under the name Hexadecimal-1, with x1 and x as acceptable aliases.

Hexadecimal-2
     This surface corresponds to an hexadecimal expression of each pair of input bytes, except for the last pair, which may be short.

     It is available in recode under the name Hexadecimal-2, with x2 for an alias.

Hexadecimal-4
     This surface corresponds to an hexadecimal expression of each quadruple of input bytes, except for the last quadruple, which may be short.

     It is available in recode under the name Hexadecimal-4, with x4 for an alias.

When removing a dump surface, that is, when reading a dump results back into a sequence of bytes, the narrower expression for a short last chunk is recognised, so dumping is a fully reversible operation.  However, in case you want to produce dumps by other means than through recode, beware that for decimal dumps, the library has to rely on the number of spaces to establish the original byte size of the chunk.

Although the library might report reversibility errors, removing a dump surface is a rather forgiving process: one may mix bases, group a variable number of data per source line, or use shorter chunks in places other than at the far end.  Also, source lines not beginning with a number are skipped.  So, recode should often be able to read a whole C header file, wrapping the results of a previous dump, and regenerate the original byte string.

Artificial data for testing
===========================

A few pseudo-surfaces exist to generate debugging data out of thin air. These surfaces are only meant for the expert recode user, and are only useful in a few contexts, like for generating binary permutations from the recoding or acting on them.

Debugging surfaces, when removed, insert their generated data at the beginning of the output stream, and copy all the input stream after the generated data, unchanged.  This strange removal constraint comes from the fact that debugging surfaces are usually specified in the before position instead of the after position within a request. With debugging surfaces, one often recodes file /dev/null in filter mode.  Specifying many debugging surfaces at once has an accumulation effect on the output, and since surfaces are removed from right to left, each generating its data at the beginning of previous output, the net effect is an impression that debugging surfaces are generated from left to right, each appending to the result of the previous.  In any case, any real input data gets appended after what was generated.

test7
     When removed, this surface produces 128 single bytes, the first having value 0, the second having value 1, and so forth until all 128 values have been generated.

test8
     When removed, this surface produces 256 single bytes, the first having value 0, the second having value 1, and so forth until all 256 values have been generated.

test15
     When removed, this surface produces 64509 double bytes, the first having value 0, the second having value 1, and so forth until all values have been generated, but excluding risky UCS-2 values, like all codes from the surrogate UCS-2 area (for UTF-16), the byte order mark, and values known as invalid UCS-2.

test16
     When removed, this surface produces 65536 double bytes, the first having value 0, the second having value 1, and so forth until all 65536 values have been generated.

As an example, the command recode l5/test8..dump < /dev/null is a convoluted way to produce an output similar to recode -lf l5.  It says to generate all possible 256 bytes and interpret them as ISO-8859-9 codes, while converting them to UCS-2.  Resulting UCS-2 characters are dumped one per line, accompanied with their explicative name.

Internal aspects
****************

The incoming explanations of the internals of recode should help people who want to dive into recode sources for adding new charsets.  Adding new charsets does not require much knowledge about the overall organisation of recode.  You can rather concentrate of your new charset, letting the remainder of the recode mechanics take care of interconnecting it with all others charsets.

If you intend to play seriously at modifying recode, beware that you may need some other GNU tools which were not required when you first installing recode.  If you modify or create any .l file, then you need Flex, and some better awk like mawk, GNU awk, or nawk.  If you modify the documentation (and you should!), you need makeinfo.  If you are really audacious, you may also want Perl for modifying tabular processing, then m4, Autoconf, Automake and libtool for adjusting configuration matters.

Overall organisation
====================

The recode mechanics slowly evolved for many years, and it would be tedious to explain all problems I met and mistakes I did all along, yielding the current behaviour.  Surely, one of the key choices was to stop trying to do all conversions in memory, one line or one buffer at a time.  It has been fruitful to use the character stream paradigm, and the elementary recoding steps now convert a whole stream to another.  Most of the control complexity in recode exists so that each elementary recoding step stays simple, making easier to add new ones.  The whole point of recode, as I see it, is providing a comfortable nest for growing new charset conversions.

The main recode driver constructs, while initialising all conversion modules, a table giving all the conversion routines available (single steps) and for each, the starting charset and the ending charset.  If we consider these charsets as being the nodes of a directed graph, each single step may be considered as oriented arc from one node to the other.  A cost is attributed to each arc: for example, a high penalty is given to single steps which are prone to losing characters, a lower penalty is given to those which need studying more than one input character for producing an output character, etc.

Given a starting code and a goal code, recode computes the most economical route through the elementary recodings, that is, the best sequence of conversions that will transform the input charset into the final charset.  To speed up execution, recode looks for subsequences of conversions which are simple enough to be merged, and then dynamically creates new single steps to represent these mergings.

A double step in recode is a special concept representing a sequence of two single steps, the output of the first single step being the special charset UCS-2, the input of the second single step being also UCS-2.  Special recode machinery dynamically produces efficient, reversible, merge-able single steps out of these double steps.

I made some statistics about how many internal recoding steps are required between any two charsets chosen at random.  The initial recoding layout, before optimisation, always uses between 1 and 5 steps.  Optimisation could sometimes produce mere copies, which are counted as no steps at all. In other cases, optimisation is unable to save any step.  The number of steps after optimisation is currently between 0 and 5 steps.  Of course, the expected number of steps is affected by optimisation: it drops from 2.8 to 1.8.  This means that recode uses a theoretical average of a bit less than one step per recoding job.  This looks good.  This was computed using reversible recodings.  In strict mode, optimisation might be defeated somewhat.  Number of steps run between 1 and 6, both before and after optimisation, and the expected number of steps decreases by a lesser amount, going from 2.2 to 1.3.  This is still manageable.

Adding new charsets
===================

The main part of recode is written in C, as are most single steps.  A few single steps need to recognise sequences of multiple characters, they are often better written in Flex.  It is easy for a programmer to add a new charset to recode.  All it requires is making a few functions kept in a single .c file, adjusting Makefile.am and remaking recode.

One of the function should convert from any previous charset to the new one.  Any previous charset will do, but try to select it so you will not lose too much information while converting.  The other function should convert from the new charset to any older one.  You do not have to select the same old charset than what you selected for the previous routine. Once again, select any charset for which you will not lose too much information while converting.

If, for any of these two functions, you have to read multiple bytes of the old charset before recognising the character to produce, you might prefer programming it in Flex in a separate .l file.  Prototype your C or Flex files after one of those which exist already, so to keep the sources uniform.  Besides, at make time, all .l files are automatically merged into a single big one by the script mergelex.awk.

There are a few hidden rules about how to write new recode modules, for allowing the automatic creation of decsteps.h and initsteps.h at make time, or the proper merging of all Flex files.  Mimetism is a simple approach which relieves me of explaining all these rules!  Start with a module closely resembling what you intend to do.  Here is some advice for picking up a model. First decide if your new charset module is to be be driven by algorithms rather than by tables.  For algorithmic recodings, see iconqnx.c for C code, or txtelat1.l for Flex code.  For table driven recodings, see ebcdic.c for one-to-one style recodings, lat1html.c for one-to-many style recodings, or atarist.c for double-step style recodings.  Just select an example from the style that better fits your application.

Each of your source files should have its own initialisation function, named module_CHARSET, which is meant to be executed quickly once, prior to any recoding.  It should declare the name of your charsets and the single steps (or elementary recodings) you provide, by calling declare_step one or more times. Besides the charset names, declare_step expects a description of the recoding quality (see recodext.h) and two functions you also provide.

The first such function has the purpose of allocating structures, pre-conditioning conversion tables, etc.  It is also the way of further modifying the STEP structure.  This function is executed if and only if the single step is retained in an actual recoding sequence. If you do not need such delayed initialisation, merely use NULL for the function argument.

The second function executes the elementary recoding on a whole file. There are a few cases when you can spare writing this function:

  * Some single steps do nothing else than a pure copy of the input onto the output, in this case, you can use the predefined function file_one_to_one, while having a delayed initialisation for presetting the STEP field one_to_one to the predefined value one_to_same.

  * Some single steps are driven by a table which recodes one character into another; if the recoding does nothing else, you can use the predefined function file_one_to_one, while having a delayed initialisation for presetting the STEP field one_to_one with your table.

  * Some single steps are driven by a table which recodes one character into a string; if the recoding does nothing else, you can use the predefined function file_one_to_many, while having a delayed initialisation for presetting the STEP field one_to_many with your table.

If you have a recoding table handy in a suitable format but do not use one of the predefined recoding functions, it is still a good idea to use a delayed initialisation to save it anyway, because recode option -h will take advantage of this information when available.

Finally, edit Makefile.am to add the source file name of your routines to the C_STEPS or L_STEPS macro definition, depending on the fact your routines is written in C or in Flex.

Adding new surfaces
===================

Adding a new surface is technically quite similar to adding a new charset. See New charsets.  A surface is provided as a set of two transformations: one from the predefined special charset data or tree to the new surface, meant to apply the surface, the other from the new surface to the predefined special charset data or tree, meant to remove the surface.

Internally in recode, function declare_step especially recognises when a charset is so related to data or tree, and then takes appropriate actions so that charset gets indeed installed as a surface.

Comments on the library design
==============================

  * Why a shared library?

     There are many different approaches to reduce system requirements to handle all tables needed in the recode library.  One of them is to have the tables in an external format and only read them in on demand. After having pondered this for a while, I finally decided against it, mainly because it involves its own kind of installation complexity, and it is not clear to me that it would be as interesting as I first imagined.

     It looks more efficient to see all tables and algorithms already mapped into virtual memory from the start of the execution, yet not loaded in actual memory, than to go through many disk accesses for opening various data files once the program is already started, as this would be needed with other solutions.  Using a shared library also has the indirect effect of making various algorithms handily available, right in the same modules providing the tables.  This alleviates much the burden of the maintenance.

     Of course, I would like to later make an exception for only a few tables, built locally by users for their own particular needs once recode is installed.  recode should just go and fetch them.  But I do not perceive this as very urgent, yet useful enough to be worth implementing.

     Currently, all tables needed for recoding are precompiled into binaries, and all these binaries are then made into a shared library.  As an initial step, I turned recode into a main program and a non-shared library, this allowed me to tidy up the API, get rid of all global variables, etc. It required a surprising amount of program source massaging.  But once this cleaned enough, it was easy to use Gordon Matzigkeit's libtool package, and take advantage of the Automake interface to neatly turn the non-shared library into a shared one.

     Sites linking with the recode library, whose system does not support any form of shared libraries, might end up with bulky executables. Surely, the recode library will have to be used statically, and might not very nicely usable on such systems.  It seems that progress has a price for those being slow at it.

     There is a locality problem I did not address yet.  Currently, the recode library takes many cycles to initialise itself, calling each module in turn for it to set up associated knowledge about charsets, aliases, elementary steps, recoding weights, etc.  Then, the recoding sequence is decided out of the command given.  I would not be surprised if initialisation was taking a perceivable fraction of a second on slower machines.  One thing to do, most probably not right in version 3.5, but the version after, would have recode to pre-load all tables and dump them at installation time.  The result would then be compiled and added to the library.  This would spare many initialisation cycles, but more importantly, would avoid calling all library modules, scattered through the virtual memory, and so, possibly causing many spurious page exceptions each time the initialisation is requested, at least once per program execution.

  * Why not a central charset?

     It would be simpler, and I would like, if something like ISO 10646 was used as a turning template for all charsets in recode.  Even if I think it could help to a certain extent, I'm still not fully sure it would be sufficient in all cases.  Moreover, some people disagree about using ISO 10646 as the central charset, to the point I cannot totally ignore them, and surely, recode is not a mean for me to force my own opinions on people.  I would like that recode be practical more than dogmatic, and reflect usage more than religions.

     Currently, if you ask recode to go from CHARSET1 to CHARSET2 chosen at random, it is highly probable that the best path will be quickly found as:

          CHARSET1..UCS-2..CHARSET2

     That is, it will almost always use the UCS as a trampoline between charsets.  However, UCS-2 will be immediately be optimised out, and CHARSET1..CHARSET2 will often be performed in a single step through a permutation table generated on the fly for the circumstance (If strict mapping is requested, another efficient device will be used instead of a permutation.).

     In those few cases where UCS-2 is not selected as a conceptual intermediate, I plan to study if it could be made so.  But I guess some cases will remain where UCS-2 is not a proper choice.  Even if UCS is often the good choice, I do not intend to forcefully restrain recode around UCS-2 (nor UCS-4) for now.  We might come to that one day, but it will come out of the natural evolution of recode. It will then reflect a fact, rather than a preset dogma.

  * Why not iconv?

     The iconv routine and library allows for converting characters from an input buffer to an input buffer, synchronously advancing both buffer cursors.  If the output buffer is not big enough to receive all of the conversion, the routine returns with the input cursor set at the position where the conversion could later be resumed, and the output cursor set to indicate until where the output buffer has been filled. Despite this scheme is simple and nice, the recode library does not offer it currently.  Why not?

     When long sequences of decodings, stepwise recodings, and re-encodings are involved, as it happens in true life, synchronising the input buffer back to where it should have stopped, when the output buffer becomes full, is a difficult problem.  Oh, we could make it simpler at the expense of loosing space or speed: by inserting markers between each input character and counting them at the output end; by processing only one character in a time through the whole sequence; by repeatedly attempting to recode various subsets of the input buffer, binary searching on their length until the output just fits.  The overhead of such solutions looks fully prohibitive to me, and the gain very minimal.  I do not see a real advantage, nowadays, imposing a fixed length to an output buffer.  It makes things so much simpler and efficient to just let the output buffer size float a bit.

     Of course, if the above problem was solved, the iconv library should be easily emulated, given that recode has similar knowledge about charsets, of course.  This either solved or not, the iconv program remains trivial (given similar knowledge about charsets). I also presume that the genxlt program would be easy too, but I do not have enough detailed specifications of it to be sure.

     A lot of years ago, recode was using a similar scheme, and I found it rather hard to manage for some cases.  I rethought the overall structure of recode for getting away from that scheme, and never regretted it. I perceive iconv as an artificial solution which surely has some elegances and virtues, but I do not find it really useful as it stands: one always has to wrap iconv into something more refined, extending it for real cases.  From past experience, I think it is unduly hard to fully implement this scheme.  It would be awkward that we do contortions for the sole purpose of implementing exactly its specification, without real, fairly sounded reasons (other then the fact some people once thought it was worth standardising).  It is much better to immediately aim for the refinement we need, without uselessly forcing us into the dubious detour iconv represents.

     Some may argue that if recode was using a comprehensive charset as a turning template, as discussed in a previous point, this would make iconv easier to implement.  Some may be tempted to say that the cases which are hard to handle are not really needed, nor interesting, anyway.  I feel and fear a bit some pressure wanting that recode be split into the part that well fits the iconv model, and the part that does not fit, considering this second part less important, with the idea of dropping it one of these days, maybe.  My guess is that users of the recode library, whatever its form, would not like to have such arbitrary limitations.  In the long run, we should not have to explain to our users that some recodings may not be made available just because they do not fit the simple model we had in mind when we did it.  Instead, we should try to stay opened to the difficulties of real life.  There is still a lot of complex needs for Asian people, say, that recode does not currently address, while it should.  Not only the doors should stay open, but we should force them wider!

Option Index
************

This is an alphabetical list of all command-line options accepted by recode.

Library Index
*************

This is an alphabetical index of important functions, data structures, and variables in the recode library.

Charset and Surface Index
*************************

This is an alphabetical list of all the charsets and surfaces supported by recode, and their aliases.