xref: /386bsd/usr/local/info/make.info-5 (revision a2142627)

This is Info file make.info, produced by Makeinfo-1.54 from the input
file ./make.texinfo.

   This file documents the GNU Make utility, which determines
automatically which pieces of a large program need to be recompiled,
and issues the commands to recompile them.

   This is Edition 0.45, last updated 11 May 1994, of `The GNU Make
Manual', for `make', Version 3.71 Beta.

   Copyright (C) 1988, '89, '90, '91, '92, '93, '94 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 Free Software Foundation.


File: make.info,  Node: Options Summary,  Prev: Testing,  Up: Running

Summary of Options
==================

   Here is a table of all the options `make' understands:

`-b'
`-m'
     These options are ignored for compatibility with other versions of
     `make'.

`-C DIR'
`--directory=DIR'
     Change to directory DIR before reading the makefiles.  If multiple
     `-C' options are specified, each is interpreted relative to the
     previous one: `-C / -C etc' is equivalent to `-C /etc'.  This is
     typically used with recursive invocations of `make' (*note
     Recursive Use of `make': Recursion.).

`-d'
`--debug'
     Print debugging information in addition to normal processing.  The
     debugging information says which files are being considered for
     remaking, which file-times are being compared and with what
     results, which files actually need to be remade, which implicit
     rules are considered and which are applied--everything interesting
     about how `make' decides what to do.

`-e'
`--environment-overrides'
     Give variables taken from the environment precedence over
     variables from makefiles.  *Note Variables from the Environment:
     Environment.

`-f FILE'
`--file=FILE'
`--makefile=FILE'
     Read the file named FILE as a makefile.  *Note Writing Makefiles:
     Makefiles.

`-h'
`--help'
     Remind you of the options that `make' understands and then exit.

`-i'
`--ignore-errors'
     Ignore all errors in commands executed to remake files.  *Note
     Errors in Commands: Errors.

`-I DIR'
`--include-dir=DIR'
     Specifies a directory DIR to search for included makefiles.  *Note
     Including Other Makefiles: Include.  If several `-I' options are
     used to specify several directories, the directories are searched
     in the order specified.

`-j [JOBS]'
`--jobs=[JOBS]'
     Specifies the number of jobs (commands) to run simultaneously.
     With no argument, `make' runs as many jobs simultaneously as
     possible.  If there is more than one `-j' option, the last one is
     effective.  *Note Parallel Execution: Parallel, for more
     information on how commands are run.

`-k'
`--keep-going'
     Continue as much as possible after an error.  While the target that
     failed, and those that depend on it, cannot be remade, the other
     dependencies of these targets can be processed all the same.
     *Note Testing the Compilation of a Program: Testing.

`-l [LOAD]'
`--load-average[=LOAD]'
`--max-load[=LOAD]'
     Specifies that no new jobs (commands) should be started if there
     are other jobs running and the load average is at least LOAD (a
     floating-point number).  With no argument, removes a previous load
     limit.  *Note Parallel Execution: Parallel.

`-n'
`--just-print'
`--dry-run'
`--recon'
     Print the commands that would be executed, but do not execute them.
     *Note Instead of Executing the Commands: Instead of Execution.

`-o FILE'
`--old-file=FILE'
`--assume-old=FILE'
     Do not remake the file FILE even if it is older than its
     dependencies, and do not remake anything on account of changes in
     FILE.  Essentially the file is treated as very old and its rules
     are ignored.  *Note Avoiding Recompilation of Some Files: Avoiding
     Compilation.

`-p'
`--print-data-base'
     Print the data base (rules and variable values) that results from
     reading the makefiles; then execute as usual or as otherwise
     specified.  This also prints the version information given by the
     `-v' switch (see below).  To print the data base without trying to
     remake any files, use `make -p -f /dev/null'.

`-q'
`--question'
     "Question mode".  Do not run any commands, or print anything; just
     return an exit status that is zero if the specified targets are
     already up to date, one if any remaking is required, or two if an
     error is encountered.  *Note Instead of Executing the Commands:
     Instead of Execution.

`-r'
`--no-builtin-rules'
     Eliminate use of the built-in implicit rules (*note Using Implicit
     Rules: Implicit Rules.).  You can still define your own by writing
     pattern rules (*note Defining and Redefining Pattern Rules:
     Pattern Rules.).  The `-r' option also clears out the default list
     of suffixes for suffix rules (*note Old-Fashioned Suffix Rules:
     Suffix Rules.).  But you can still define your own suffixes with a
     rule for `.SUFFIXES', and then define your own suffix rules.

`-s'
`--silent'
`--quiet'
     Silent operation; do not print the commands as they are executed.
     *Note Command Echoing: Echoing.

`-S'
`--no-keep-going'
`--stop'
     Cancel the effect of the `-k' option.  This is never necessary
     except in a recursive `make' where `-k' might be inherited from
     the top-level `make' via `MAKEFLAGS' (*note Recursive Use of
     `make': Recursion.) or if you set `-k' in `MAKEFLAGS' in your
     environment.

`-t'
`--touch'
     Touch files (mark them up to date without really changing them)
     instead of running their commands.  This is used to pretend that
     the commands were done, in order to fool future invocations of
     `make'.  *Note Instead of Executing the Commands: Instead of
     Execution.

`-v'
`--version'
     Print the version of the `make' program plus a copyright, a list
     of authors, and a notice that there is no warranty; then exit.

`-w'
`--print-directory'
     Print a message containing the working directory both before and
     after executing the makefile.  This may be useful for tracking
     down errors from complicated nests of recursive `make' commands.
     *Note Recursive Use of `make': Recursion.  (In practice, you
     rarely need to specify this option since `make' does it for you;
     see *Note The `--print-directory' Option: -w Option.)

`--no-print-directory'
     Disable printing of the working directory under `-w'.  This option
     is useful when `-w' is turned on automatically, but you do not
     want to see the extra messages.  *Note The `--print-directory'
     Option: -w Option.

`-W FILE'
`--what-if=FILE'
`--new-file=FILE'
`--assume-new=FILE'
     Pretend that the target FILE has just been modified.  When used
     with the `-n' flag, this shows you what would happen if you were
     to modify that file.  Without `-n', it is almost the same as
     running a `touch' command on the given file before running `make',
     except that the modification time is changed only in the
     imagination of `make'.  *Note Instead of Executing the Commands:
     Instead of Execution.

`--warn-undefined-variables'
     Issue a warning message whenever `make' sees a reference to an
     undefined variable.  This can be helpful when you are trying to
     debug makefiles which use variables in complex ways.


File: make.info,  Node: Implicit Rules,  Next: Archives,  Prev: Running,  Up: Top

Using Implicit Rules
********************

   Certain standard ways of remaking target files are used very often.
For example, one customary way to make an object file is from a C
source file using the C compiler, `cc'.

   "Implicit rules" tell `make' how to use customary techniques so that
you do not have to specify them in detail when you want to use them.
For example, there is an implicit rule for C compilation.  File names
determine which implicit rules are run.  For example, C compilation
typically takes a `.c' file and makes a `.o' file.  So `make' applies
the implicit rule for C compilation when it sees this combination of
file name endings.

   A chain of implicit rules can apply in sequence; for example, `make'
will remake a `.o' file from a `.y' file by way of a `.c' file.

   The built-in implicit rules use several variables in their commands
so that, by changing the values of the variables, you can change the
way the implicit rule works.  For example, the variable `CFLAGS'
controls the flags given to the C compiler by the implicit rule for C
compilation.

   You can define your own implicit rules by writing "pattern rules".

   "Suffix rules" are a more limited way to define implicit rules.
Pattern rules are more general and clearer, but suffix rules are
retained for compatibility.

* Menu:

* Using Implicit::              How to use an existing implicit rule
                                  to get the commands for updating a file.
* Catalogue of Rules::          A list of built-in implicit rules.
* Implicit Variables::          How to change what predefined rules do.
* Chained Rules::               How to use a chain of implicit rules.
* Pattern Rules::               How to define new implicit rules.
* Last Resort::                 How to defining commands for rules
                                  which cannot find any.
* Suffix Rules::                The old-fashioned style of implicit rule.
* Search Algorithm::            The precise algorithm for applying
                                  implicit rules.


File: make.info,  Node: Using Implicit,  Next: Catalogue of Rules,  Up: Implicit Rules

Using Implicit Rules
====================

   To allow `make' to find a customary method for updating a target
file, all you have to do is refrain from specifying commands yourself.
Either write a rule with no command lines, or don't write a rule at
all.  Then `make' will figure out which implicit rule to use based on
which kind of source file exists or can be made.

   For example, suppose the makefile looks like this:

     foo : foo.o bar.o
             cc -o foo foo.o bar.o $(CFLAGS) $(LDFLAGS)

Because you mention `foo.o' but do not give a rule for it, `make' will
automatically look for an implicit rule that tells how to update it.
This happens whether or not the file `foo.o' currently exists.

   If an implicit rule is found, it can supply both commands and one or
more dependencies (the source files).  You would want to write a rule
for `foo.o' with no command lines if you need to specify additional
dependencies, such as header files, that the implicit rule cannot
supply.

   Each implicit rule has a target pattern and dependency patterns.
There may be many implicit rules with the same target pattern.  For
example, numerous rules make `.o' files: one, from a `.c' file with the
C compiler; another, from a `.p' file with the Pascal compiler; and so
on.  The rule that actually applies is the one whose dependencies exist
or can be made.  So, if you have a file `foo.c', `make' will run the C
compiler; otherwise, if you have a file `foo.p', `make' will run the
Pascal compiler; and so on.

   Of course, when you write the makefile, you know which implicit rule
you want `make' to use, and you know it will choose that one because you
know which possible dependency files are supposed to exist.  *Note
Catalogue of Implicit Rules: Catalogue of Rules, for a catalogue of all
the predefined implicit rules.

   Above, we said an implicit rule applies if the required dependencies
"exist or can be made".  A file "can be made" if it is mentioned
explicitly in the makefile as a target or a dependency, or if an
implicit rule can be recursively found for how to make it.  When an
implicit dependency is the result of another implicit rule, we say that
"chaining" is occurring.  *Note Chains of Implicit Rules: Chained Rules.

   In general, `make' searches for an implicit rule for each target, and
for each double-colon rule, that has no commands.  A file that is
mentioned only as a dependency is considered a target whose rule
specifies nothing, so implicit rule search happens for it.  *Note
Implicit Rule Search Algorithm: Search Algorithm, for the details of
how the search is done.

   Note that explicit dependencies do not influence implicit rule
search.  For example, consider this explicit rule:

     foo.o: foo.p

The dependency on `foo.p' does not necessarily mean that `make' will
remake `foo.o' according to the implicit rule to make an object file, a
`.o' file, from a Pascal source file, a `.p' file.  For example, if
`foo.c' also exists, the implicit rule to make an object file from a C
source file is used instead, because it appears before the Pascal rule
in the list of predefined implicit rules (*note Catalogue of Implicit
Rules: Catalogue of Rules.).

   If you do not want an implicit rule to be used for a target that has
no commands, you can give that target empty commands by writing a
semicolon (*note Defining Empty Commands: Empty Commands.).


File: make.info,  Node: Catalogue of Rules,  Next: Implicit Variables,  Prev: Using Implicit,  Up: Implicit Rules

Catalogue of Implicit Rules
===========================

   Here is a catalogue of predefined implicit rules which are always
available unless the makefile explicitly overrides or cancels them.
*Note Canceling Implicit Rules: Canceling Rules, for information on
canceling or overriding an implicit rule.  The `-r' or
`--no-builtin-rules' option cancels all predefined rules.

   Not all of these rules will always be defined, even when the `-r'
option is not given.  Many of the predefined implicit rules are
implemented in `make' as suffix rules, so which ones will be defined
depends on the "suffix list" (the list of dependencies of the special
target `.SUFFIXES').  The default suffix list is: `.out', `.a', `.ln',
`.o', `.c', `.cc', `.C', `.p', `.f', `.F', `.r', `.y', `.l', `.s',
`.S', `.mod', `.sym', `.def', `.h', `.info', `.dvi', `.tex', `.texinfo',
`.texi', `.txinfo', `.w', `.ch' `.web', `.sh', `.elc', `.el'.  All of
the implicit rules described below whose dependencies have one of these
suffixes are actually suffix rules.  If you modify the suffix list, the
only predefined suffix rules in effect will be those named by one or
two of the suffixes that are on the list you specify; rules whose
suffixes fail to be on the list are disabled.  *Note Old-Fashioned
Suffix Rules: Suffix Rules, for full details on suffix rules.

Compiling C programs
     `N.o' is made automatically from `N.c' with a command of the form
     `$(CC) -c $(CPPFLAGS) $(CFLAGS)'.

Compiling C++ programs
     `N.o' is made automatically from `N.cc' or `N.C' with a command of
     the form `$(CXX) -c $(CPPFLAGS) $(CXXFLAGS)'.  We encourage you to
     use the suffix `.cc' for C++ source files instead of `.C'.

Compiling Pascal programs
     `N.o' is made automatically from `N.p' with the command `$(PC) -c
     $(PFLAGS)'.

Compiling Fortran and Ratfor programs
     `N.o' is made automatically from `N.r', `N.F' or `N.f' by running
     the Fortran compiler.  The precise command used is as follows:

    `.f'
          `$(FC) -c $(FFLAGS)'.

    `.F'
          `$(FC) -c $(FFLAGS) $(CPPFLAGS)'.

    `.r'
          `$(FC) -c $(FFLAGS) $(RFLAGS)'.

Preprocessing Fortran and Ratfor programs
     `N.f' is made automatically from `N.r' or `N.F'.  This rule runs
     just the preprocessor to convert a Ratfor or preprocessable
     Fortran program into a strict Fortran program.  The precise
     command used is as follows:

    `.F'
          `$(FC) -F $(CPPFLAGS) $(FFLAGS)'.

    `.r'
          `$(FC) -F $(FFLAGS) $(RFLAGS)'.

Compiling Modula-2 programs
     `N.sym' is made from `N.def' with a command of the form `$(M2C)
     $(M2FLAGS) $(DEFFLAGS)'.  `N.o' is made from `N.mod'; the form is:
     `$(M2C) $(M2FLAGS) $(MODFLAGS)'.

Assembling and preprocessing assembler programs
     `N.o' is made automatically from `N.s' by running the assembler,
     `as'.  The precise command is `$(AS) $(ASFLAGS)'.

     `N.s' is made automatically from `N.S' by running the C
     preprocessor, `cpp'.  The precise command is `$(CPP) $(CPPFLAGS)'.

Linking a single object file
     `N' is made automatically from `N.o' by running the linker
     (usually called `ld') via the C compiler.  The precise command
     used is `$(CC) $(LDFLAGS) N.o $(LOADLIBES)'.

     This rule does the right thing for a simple program with only one
     source file.  It will also do the right thing if there are multiple
     object files (presumably coming from various other source files),
     one of which has a name matching that of the executable file.
     Thus,

          x: y.o z.o

     when `x.c', `y.c' and `z.c' all exist will execute:

          cc -c x.c -o x.o
          cc -c y.c -o y.o
          cc -c z.c -o z.o
          cc x.o y.o z.o -o x
          rm -f x.o
          rm -f y.o
          rm -f z.o

     In more complicated cases, such as when there is no object file
     whose name derives from the executable file name, you must write
     an explicit command for linking.

     Each kind of file automatically made into `.o' object files will
     be automatically linked by using the compiler (`$(CC)', `$(FC)' or
     `$(PC)'; the C compiler `$(CC)' is used to assemble `.s' files)
     without the `-c' option.  This could be done by using the `.o'
     object files as intermediates, but it is faster to do the
     compiling and linking in one step, so that's how it's done.

Yacc for C programs
     `N.c' is made automatically from `N.y' by running Yacc with the
     command `$(YACC) $(YFLAGS)'.

Lex for C programs
     `N.c' is made automatically from `N.l' by by running Lex.  The
     actual command is `$(LEX) $(LFLAGS)'.

Lex for Ratfor programs
     `N.r' is made automatically from `N.l' by by running Lex.  The
     actual command is `$(LEX) $(LFLAGS)'.

     The convention of using the same suffix `.l' for all Lex files
     regardless of whether they produce C code or Ratfor code makes it
     impossible for `make' to determine automatically which of the two
     languages you are using in any particular case.  If `make' is
     called upon to remake an object file from a `.l' file, it must
     guess which compiler to use.  It will guess the C compiler, because
     that is more common.  If you are using Ratfor, make sure `make'
     knows this by mentioning `N.r' in the makefile.  Or, if you are
     using Ratfor exclusively, with no C files, remove `.c' from the
     list of implicit rule suffixes with:

          .SUFFIXES:
          .SUFFIXES: .o .r .f .l ...

Making Lint Libraries from C, Yacc, or Lex programs
     `N.ln' is made from `N.c' by running `lint'.  The precise command
     is `$(LINT) $(LINTFLAGS) $(CPPFLAGS) -i'.  The same command is
     used on the C code produced from `N.y' or `N.l'.

TeX and Web
     `N.dvi' is made from `N.tex' with the command `$(TEX)'.  `N.tex'
     is made from `N.web' with `$(WEAVE)', or from `N.w' (and from
     `N.ch' if it exists or can be made) with `$(CWEAVE)'.  `N.p' is
     made from `N.web' with `$(TANGLE)' and `N.c' is made from `N.w'
     (and from `N.ch' if it exists or can be made) with `$(CTANGLE)'.

Texinfo and Info
     `N.dvi' is made from `N.texinfo', `N.texi', or `N.txinfo', with
     the command `$(TEXI2DVI) $(TEXI2DVI_FLAGS)'.  `N.info' is made from
     `N.texinfo', `N.texi', or `N.txinfo', with the command
     `$(MAKEINFO) $(MAKEINFO_FLAGS)'.

RCS
     Any file `N' is extracted if necessary from an RCS file named
     either `N,v' or `RCS/N,v'.  The precise command used is
     `$(CO) $(COFLAGS)'.  `N' will not be extracted from RCS if it
     already exists, even if the RCS file is newer.  The rules for RCS
     are terminal (*note Match-Anything Pattern Rules: Match-Anything
     Rules.), so RCS files cannot be generated from another source;
     they must actually exist.

SCCS
     Any file `N' is extracted if necessary from an SCCS file named
     either `s.N' or `SCCS/s.N'.  The precise command used is
     `$(GET) $(GFLAGS)'.  The rules for SCCS are terminal (*note
     Match-Anything Pattern Rules: Match-Anything Rules.), so SCCS
     files cannot be generated from another source; they must actually
     exist.

     For the benefit of SCCS, a file `N' is copied from `N.sh' and made
     executable (by everyone).  This is for shell scripts that are
     checked into SCCS.  Since RCS preserves the execution permission
     of a file, you do not need to use this feature with RCS.

     We recommend that you avoid using of SCCS.  RCS is widely held to
     be superior, and is also free.  By choosing free software in place
     of comparable (or inferior) proprietary software, you support the
     free software movement.

   Usually, you want to change only the variables listed in the table
above, which are documented in the following section.

   However, the commands in built-in implicit rules actually use
variables such as `COMPILE.c', `LINK.p', and `PREPROCESS.S', whose
values contain the commands listed above.

   `make' follows the convention that the rule to compile a `.X' source
file uses the variable `COMPILE.X'.  Similarly, the rule to produce an
executable from a `.X' file uses `LINK.X'; and the rule to preprocess a
`.X' file uses `PREPROCESS.X'.

   Every rule that produces an object file uses the variable
`OUTPUT_OPTION'.  `make' defines this variable either to contain `-o
$@', or to be empty, depending on a compile-time option.  You need the
`-o' option to ensure that the output goes into the right file when the
source file is in a different directory, as when using `VPATH' (*note
Directory Search::.).  However, compilers on some systems do not accept
a `-o' switch for object files.  If you use such a system, and use
`VPATH', some compilations will put their output in the wrong place.  A
possible workaround for this problem is to give `OUTPUT_OPTION' the
value `; mv $*.o $@'.


File: make.info,  Node: Implicit Variables,  Next: Chained Rules,  Prev: Catalogue of Rules,  Up: Implicit Rules

Variables Used by Implicit Rules
================================

   The commands in built-in implicit rules make liberal use of certain
predefined variables.  You can alter these variables in the makefile,
with arguments to `make', or in the environment to alter how the
implicit rules work without redefining the rules themselves.

   For example, the command used to compile a C source file actually
says `$(CC) -c $(CFLAGS) $(CPPFLAGS)'.  The default values of the
variables used are `cc' and nothing, resulting in the command `cc -c'.
By redefining `CC' to `ncc', you could cause `ncc' to be used for all C
compilations performed by the implicit rule.  By redefining `CFLAGS' to
be `-g', you could pass the `-g' option to each compilation.  *All*
implicit rules that do C compilation use `$(CC)' to get the program
name for the compiler and *all* include `$(CFLAGS)' among the arguments
given to the compiler.

   The variables used in implicit rules fall into two classes: those
that are names of programs (like `CC') and those that contain arguments
for the programs (like `CFLAGS').  (The "name of a program" may also
contain some command arguments, but it must start with an actual
executable program name.)  If a variable value contains more than one
argument, separate them with spaces.

   Here is a table of variables used as names of programs in built-in
rules:

`AR'
     Archive-maintaining program; default `ar'.

`AS'
     Program for doing assembly; default `as'.

`CC'
     Program for compiling C programs; default `cc'.

`CXX'
     Program for compiling C++ programs; default `g++'.

`CO'
     Program for extracting a file from RCS; default `co'.

`CPP'
     Program for running the C preprocessor, with results to standard
     output; default `$(CC) -E'.

`FC'
     Program for compiling or preprocessing Fortran and Ratfor programs;
     default `f77'.

`GET'
     Program for extracting a file from SCCS; default `get'.

`LEX'
     Program to use to turn Lex grammars into C programs or Ratfor
     programs; default `lex'.

`PC'
     Program for compiling Pascal programs; default `pc'.

`YACC'
     Program to use to turn Yacc grammars into C programs; default
     `yacc'.

`YACCR'
     Program to use to turn Yacc grammars into Ratfor programs; default
     `yacc -r'.

`MAKEINFO'
     Program to convert a Texinfo source file into an Info file; default
     `makeinfo'.

`TEX'
     Program to make TeX DVI files from TeX source; default `tex'.

`TEXI2DVI'
     Program to make TeX DVI files from Texinfo source; default
     `texi2dvi'.

`WEAVE'
     Program to translate Web into TeX; default `weave'.

`CWEAVE'
     Program to translate C Web into TeX; default `cweave'.

`TANGLE'
     Program to translate Web into Pascal; default `tangle'.

`CTANGLE'
     Program to translate C Web into C; default `ctangle'.

`RM'
     Command to remove a file; default `rm -f'.

   Here is a table of variables whose values are additional arguments
for the programs above.  The default values for all of these is the
empty string, unless otherwise noted.

`ARFLAGS'
     Flags to give the archive-maintaining program; default `rv'.

`ASFLAGS'
     Extra flags to give to the assembler (when explicitly invoked on a
     `.s' or `.S' file).

`CFLAGS'
     Extra flags to give to the C compiler.

`CXXFLAGS'
     Extra flags to give to the C++ compiler.

`COFLAGS'
     Extra flags to give to the RCS `co' program.

`CPPFLAGS'
     Extra flags to give to the C preprocessor and programs that use it
     (the C and Fortran compilers).

`FFLAGS'
     Extra flags to give to the Fortran compiler.

`GFLAGS'
     Extra flags to give to the SCCS `get' program.

`LDFLAGS'
     Extra flags to give to compilers when they are supposed to invoke
     the linker, `ld'.

`LFLAGS'
     Extra flags to give to Lex.

`PFLAGS'
     Extra flags to give to the Pascal compiler.

`RFLAGS'
     Extra flags to give to the Fortran compiler for Ratfor programs.

`YFLAGS'
     Extra flags to give to Yacc.


File: make.info,  Node: Chained Rules,  Next: Pattern Rules,  Prev: Implicit Variables,  Up: Implicit Rules

Chains of Implicit Rules
========================

   Sometimes a file can be made by a sequence of implicit rules.  For
example, a file `N.o' could be made from `N.y' by running first Yacc
and then `cc'.  Such a sequence is called a "chain".

   If the file `N.c' exists, or is mentioned in the makefile, no
special searching is required: `make' finds that the object file can be
made by C compilation from `N.c'; later on, when considering how to
make `N.c', the rule for running Yacc is used.  Ultimately both `N.c'
and `N.o' are updated.

   However, even if `N.c' does not exist and is not mentioned, `make'
knows how to envision it as the missing link between `N.o' and `N.y'!
In this case, `N.c' is called an "intermediate file".  Once `make' has
decided to use the intermediate file, it is entered in the data base as
if it had been mentioned in the makefile, along with the implicit rule
that says how to create it.

   Intermediate files are remade using their rules just like all other
files.  The difference is that the intermediate file is deleted when
`make' is finished.  Therefore, the intermediate file which did not
exist before `make' also does not exist after `make'.  The deletion is
reported to you by printing a `rm -f' command that shows what `make' is
doing.  (You can list the target pattern of an implicit rule (such as
`%.o') as a dependency of the special target `.PRECIOUS' to preserve
intermediate files made by implicit rules whose target patterns match
that file's name; see *Note Interrupts::.)

   A chain can involve more than two implicit rules.  For example, it is
possible to make a file `foo' from `RCS/foo.y,v' by running RCS, Yacc
and `cc'.  Then both `foo.y' and `foo.c' are intermediate files that
are deleted at the end.

   No single implicit rule can appear more than once in a chain.  This
means that `make' will not even consider such a ridiculous thing as
making `foo' from `foo.o.o' by running the linker twice.  This
constraint has the added benefit of preventing any infinite loop in the
search for an implicit rule chain.

   There are some special implicit rules to optimize certain cases that
would otherwise be handled by rule chains.  For example, making `foo'
from `foo.c' could be handled by compiling and linking with separate
chained rules, using `foo.o' as an intermediate file.  But what
actually happens is that a special rule for this case does the
compilation and linking with a single `cc' command.  The optimized rule
is used in preference to the step-by-step chain because it comes
earlier in the ordering of rules.


File: make.info,  Node: Pattern Rules,  Next: Last Resort,  Prev: Chained Rules,  Up: Implicit Rules

Defining and Redefining Pattern Rules
=====================================

   You define an implicit rule by writing a "pattern rule".  A pattern
rule looks like an ordinary rule, except that its target contains the
character `%' (exactly one of them).  The target is considered a
pattern for matching file names; the `%' can match any nonempty
substring, while other characters match only themselves.  The
dependencies likewise use `%' to show how their names relate to the
target name.

   Thus, a pattern rule `%.o : %.c' says how to make any file `STEM.o'
from another file `STEM.c'.

   Note that expansion using `%' in pattern rules occurs *after* any
variable or function expansions, which take place when the makefile is
read.  *Note How to Use Variables: Using Variables, and *Note Functions
for Transforming Text: Functions.

* Menu:

* Pattern Intro::               An introduction to pattern rules.
* Pattern Examples::            Examples of pattern rules.
* Automatic::                   How to use automatic variables in the
                                  commands of implicit rules.
* Pattern Match::               How patterns match.
* Match-Anything Rules::        Precautions you should take prior to
                                  defining rules that can match any
                                  target file whatever.
* Canceling Rules::             How to override or cancel built-in rules.


File: make.info,  Node: Pattern Intro,  Next: Pattern Examples,  Up: Pattern Rules

Introduction to Pattern Rules
-----------------------------

   A pattern rule contains the character `%' (exactly one of them) in
the target; otherwise, it looks exactly like an ordinary rule.  The
target is a pattern for matching file names; the `%' matches any
nonempty substring, while other characters match only themselves.

   For example, `%.c' as a pattern matches any file name that ends in
`.c'.  `s.%.c' as a pattern matches any file name that starts with
`s.', ends in `.c' and is at least five characters long.  (There must
be at least one character to match the `%'.)  The substring that the
`%' matches is called the "stem".

   `%' in a dependency of a pattern rule stands for the same stem that
was matched by the `%' in the target.  In order for the pattern rule to
apply, its target pattern must match the file name under consideration,
and its dependency patterns must name files that exist or can be made.
These files become dependencies of the target.

   Thus, a rule of the form

     %.o : %.c ; COMMAND...

specifies how to make a file `N.o', with another file `N.c' as its
dependency, provided that `N.c' exists or can be made.

   There may also be dependencies that do not use `%'; such a dependency
attaches to every file made by this pattern rule.  These unvarying
dependencies are useful occasionally.

   A pattern rule need not have any dependencies that contain `%', or
in fact any dependencies at all.  Such a rule is effectively a general
wildcard.  It provides a way to make any file that matches the target
pattern.  *Note Last Resort::.

   Pattern rules may have more than one target.  Unlike normal rules,
this does not act as many different rules with the same dependencies and
commands.  If a pattern rule has multiple targets, `make' knows that
the rule's commands are responsible for making all of the targets.  The
commands are executed only once to make all the targets.  When searching
for a pattern rule to match a target, the target patterns of a rule
other than the one that matches the target in need of a rule are
incidental: `make' worries only about giving commands and dependencies
to the file presently in question.  However, when this file's commands
are run, the other targets are marked as having been updated themselves.

   The order in which pattern rules appear in the makefile is important
since this is the order in which they are considered.  Of equally
applicable rules, only the first one found is used.  The rules you
write take precedence over those that are built in.  Note however, that
a rule whose dependencies actually exist or are mentioned always takes
priority over a rule with dependencies that must be made by chaining
other implicit rules.


File: make.info,  Node: Pattern Examples,  Next: Automatic,  Prev: Pattern Intro,  Up: Pattern Rules

Pattern Rule Examples
---------------------

   Here are some examples of pattern rules actually predefined in
`make'.  First, the rule that compiles `.c' files into `.o' files:

     %.o : %.c
             $(CC) -c $(CFLAGS) $(CPPFLAGS) $< -o $@

defines a rule that can make any file `X.o' from `X.c'.  The command
uses the automatic variables `$@' and `$<' to substitute the names of
the target file and the source file in each case where the rule applies
(*note Automatic Variables: Automatic.).

   Here is a second built-in rule:

     % :: RCS/%,v
             $(CO) $(COFLAGS) $<

defines a rule that can make any file `X' whatsoever from a
corresponding file `X,v' in the subdirectory `RCS'.  Since the target
is `%', this rule will apply to any file whatever, provided the
appropriate dependency file exists.  The double colon makes the rule
"terminal", which means that its dependency may not be an intermediate
file (*note Match-Anything Pattern Rules: Match-Anything Rules.).

   This pattern rule has two targets:

     %.tab.c %.tab.h: %.y
             bison -d $<

This tells `make' that the command `bison -d X.y' will make both
`X.tab.c' and `X.tab.h'.  If the file `foo' depends on the files
`parse.tab.o' and `scan.o' and the file `scan.o' depends on the file
`parse.tab.h', when `parse.y' is changed, the command `bison -d parse.y'
will be executed only once, and the dependencies of both `parse.tab.o'
and `scan.o' will be satisfied.  (Presumably the file `parse.tab.o'
will be recompiled from `parse.tab.c' and the file `scan.o' from
`scan.c', while `foo' is linked from `parse.tab.o', `scan.o', and its
other dependencies, and it will execute happily ever after.)


File: make.info,  Node: Automatic,  Next: Pattern Match,  Prev: Pattern Examples,  Up: Pattern Rules

Automatic Variables
-------------------

   Suppose you are writing a pattern rule to compile a `.c' file into a
`.o' file: how do you write the `cc' command so that it operates on the
right source file name?  You cannot write the name in the command,
because the name is different each time the implicit rule is applied.

   What you do is use a special feature of `make', the "automatic
variables".  These variables have values computed afresh for each rule
that is executed, based on the target and dependencies of the rule.  In
this example, you would use `$@' for the object file name and `$<' for
the source file name.

   Here is a table of automatic variables:

`$@'
     The file name of the target of the rule.  If the target is an
     archive member, then `$@' is the name of the archive file.  In a
     pattern rule that has multiple targets (*note Introduction to
     Pattern Rules: Pattern Intro.), `$@' is the name of whichever
     target caused the rule's commands to be run.

`$%'
     The target member name, when the target is an archive member.
     *Note Archives::.  For example, if the target is `foo.a(bar.o)'
     then `$%' is `bar.o' and `$@' is `foo.a'.  `$%' is empty when the
     target is not an archive member.

`$<'
     The name of the first dependency.  If the target got its commands
     from an implicit rule, this will be the first dependency added by
     the implicit rule (*note Implicit Rules::.).

`$?'
     The names of all the dependencies that are newer than the target,
     with spaces between them.  For dependencies which are archive
     members, only the member named is used (*note Archives::.).

`$^'
     The names of all the dependencies, with spaces between them.  For
     dependencies which are archive members, only the member named is
     used (*note Archives::.).  A target has only one dependency on
     each other file it depends on, no matter how many times each file
     is listed as a dependency.  So if you list a dependency more than
     once for a target, the value of `$^' contains just one copy of the
     name.

`$*'
     The stem with which an implicit rule matches (*note How Patterns
     Match: Pattern Match.).  If the target is `dir/a.foo.b' and the
     target pattern is `a.%.b' then the stem is `dir/foo'.  The stem is
     useful for constructing names of related files.

     In a static pattern rule, the stem is part of the file name that
     matched the `%' in the target pattern.

     In an explicit rule, there is no stem; so `$*' cannot be determined
     in that way.  Instead, if the target name ends with a recognized
     suffix (*note Old-Fashioned Suffix Rules: Suffix Rules.), `$*' is
     set to the target name minus the suffix.  For example, if the
     target name is `foo.c', then `$*' is set to `foo', since `.c' is a
     suffix.  GNU `make' does this bizarre thing only for compatibility
     with other implementations of `make'.  You should generally avoid
     using `$*' except in implicit rules or static pattern rules.

     If the target name in an explicit rule does not end with a
     recognized suffix, `$*' is set to the empty string for that rule.

   `$?' is useful even in explicit rules when you wish to operate on
only the dependencies that have changed.  For example, suppose that an
archive named `lib' is supposed to contain copies of several object
files.  This rule copies just the changed object files into the archive:

     lib: foo.o bar.o lose.o win.o
             ar r lib $?

   Of the variables listed above, four have values that are single file
names, and two have values that are lists of file names.  These six have
variants that get just the file's directory name or just the file name
within the directory.  The variant variables' names are formed by
appending `D' or `F', respectively.  These variants are semi-obsolete
in GNU `make' since the functions `dir' and `notdir' can be used to get
a similar effect (*note Functions for File Names: Filename Functions.).
Note, however, that the `F' variants all omit the trailing slash which
always appears in the output of the `dir' function.  Here is a table of
the variants:

`$(@D)'
     The directory part of the file name of the target, with the
     trailing slash removed.  If the value of `$@' is `dir/foo.o' then
     `$(@D)' is `dir'.  This value is `.' if `$@' does not contain a
     slash.

`$(@F)'
     The file-within-directory part of the file name of the target.  If
     the value of `$@' is `dir/foo.o' then `$(@F)' is `foo.o'.  `$(@F)'
     is equivalent to `$(notdir $@)'.

`$(*D)'
`$(*F)'
     The directory part and the file-within-directory part of the stem;
     `dir' and `foo' in this example.

`$(%D)'
`$(%F)'
     The directory part and the file-within-directory part of the target
     archive member name.  This makes sense only for archive member
     targets of the form `ARCHIVE(MEMBER)' and is useful only when
     MEMBER may contain a directory name.  (*Note Archive Members as
     Targets: Archive Members.)

`$(<D)'
`$(<F)'
     The directory part and the file-within-directory part of the first
     dependency.

`$(^D)'
`$(^F)'
     Lists of the directory parts and the file-within-directory parts
     of all dependencies.

`$(?D)'
`$(?F)'
     Lists of the directory parts and the file-within-directory parts of
     all dependencies that are newer than the target.

   Note that we use a special stylistic convention when we talk about
these automatic variables; we write "the value of `$<'", rather than
"the variable `<'" as we would write for ordinary variables such as
`objects' and `CFLAGS'.  We think this convention looks more natural in
this special case.  Please do not assume it has a deep significance;
`$<' refers to the variable named `<' just as `$(CFLAGS)' refers to the
variable named `CFLAGS'.  You could just as well use `$(<)' in place of
`$<'.


File: make.info,  Node: Pattern Match,  Next: Match-Anything Rules,  Prev: Automatic,  Up: Pattern Rules

How Patterns Match
------------------

   A target pattern is composed of a `%' between a prefix and a suffix,
either or both of which may be empty.  The pattern matches a file name
only if the file name starts with the prefix and ends with the suffix,
without overlap.  The text between the prefix and the suffix is called
the "stem".  Thus, when the pattern `%.o' matches the file name
`test.o', the stem is `test'.  The pattern rule dependencies are turned
into actual file names by substituting the stem for the character `%'.
Thus, if in the same example one of the dependencies is written as
`%.c', it expands to `test.c'.

   When the target pattern does not contain a slash (and it usually does
not), directory names in the file names are removed from the file name
before it is compared with the target prefix and suffix.  After the
comparison of the file name to the target pattern, the directory names,
along with the slash that ends them, are added on to the dependency
file names generated from the pattern rule's dependency patterns and
the file name. The directories are ignored only for the purpose of
finding an implicit rule to use, not in the application of that rule.
Thus, `e%t' matches the file name `src/eat', with `src/a' as the stem.
When dependencies are turned into file names, the directories from the
stem are added at the front, while the rest of the stem is substituted
for the `%'.  The stem `src/a' with a dependency pattern `c%r' gives
the file name `src/car'.


File: make.info,  Node: Match-Anything Rules,  Next: Canceling Rules,  Prev: Pattern Match,  Up: Pattern Rules

Match-Anything Pattern Rules
----------------------------

   When a pattern rule's target is just `%', it matches any file name
whatever.  We call these rules "match-anything" rules.  They are very
useful, but it can take a lot of time for `make' to think about them,
because it must consider every such rule for each file name listed
either as a target or as a dependency.

   Suppose the makefile mentions `foo.c'.  For this target, `make'
would have to consider making it by linking an object file `foo.c.o',
or by C compilation-and-linking in one step from `foo.c.c', or by
Pascal compilation-and-linking from `foo.c.p', and many other
possibilities.

   We know these possibilities are ridiculous since `foo.c' is a C
source file, not an executable.  If `make' did consider these
possibilities, it would ultimately reject them, because files such as
`foo.c.o' and `foo.c.p' would not exist.  But these possibilities are so
numerous that `make' would run very slowly if it had to consider them.

   To gain speed, we have put various constraints on the way `make'
considers match-anything rules.  There are two different constraints
that can be applied, and each time you define a match-anything rule you
must choose one or the other for that rule.

   One choice is to mark the match-anything rule as "terminal" by
defining it with a double colon.  When a rule is terminal, it does not
apply unless its dependencies actually exist.  Dependencies that could
be made with other implicit rules are not good enough.  In other words,
no further chaining is allowed beyond a terminal rule.

   For example, the built-in implicit rules for extracting sources from
RCS and SCCS files are terminal; as a result, if the file `foo.c,v' does
not exist, `make' will not even consider trying to make it as an
intermediate file from `foo.c,v.o' or from `RCS/SCCS/s.foo.c,v'.  RCS
and SCCS files are generally ultimate source files, which should not be
remade from any other files; therefore, `make' can save time by not
looking for ways to remake them.

   If you do not mark the match-anything rule as terminal, then it is
nonterminal.  A nonterminal match-anything rule cannot apply to a file
name that indicates a specific type of data.  A file name indicates a
specific type of data if some non-match-anything implicit rule target
matches it.

   For example, the file name `foo.c' matches the target for the pattern
rule `%.c : %.y' (the rule to run Yacc).  Regardless of whether this
rule is actually applicable (which happens only if there is a file
`foo.y'), the fact that its target matches is enough to prevent
consideration of any nonterminal match-anything rules for the file
`foo.c'.  Thus, `make' will not even consider trying to make `foo.c' as
an executable file from `foo.c.o', `foo.c.c', `foo.c.p', etc.

   The motivation for this constraint is that nonterminal match-anything
rules are used for making files containing specific types of data (such
as executable files) and a file name with a recognized suffix indicates
some other specific type of data (such as a C source file).

   Special built-in dummy pattern rules are provided solely to recognize
certain file names so that nonterminal match-anything rules will not be
considered.  These dummy rules have no dependencies and no commands, and
they are ignored for all other purposes.  For example, the built-in
implicit rule

     %.p :

exists to make sure that Pascal source files such as `foo.p' match a
specific target pattern and thereby prevent time from being wasted
looking for `foo.p.o' or `foo.p.c'.

   Dummy pattern rules such as the one for `%.p' are made for every
suffix listed as valid for use in suffix rules (*note Old-Fashioned
Suffix Rules: Suffix Rules.).


File: make.info,  Node: Canceling Rules,  Prev: Match-Anything Rules,  Up: Pattern Rules

Canceling Implicit Rules
------------------------

   You can override a built-in implicit rule (or one you have defined
yourself) by defining a new pattern rule with the same target and
dependencies, but different commands.  When the new rule is defined, the
built-in one is replaced.  The new rule's position in the sequence of
implicit rules is determined by where you write the new rule.

   You can cancel a built-in implicit rule by defining a pattern rule
with the same target and dependencies, but no commands.  For example,
the following would cancel the rule that runs the assembler:

     %.o : %.s


File: make.info,  Node: Last Resort,  Next: Suffix Rules,  Prev: Pattern Rules,  Up: Implicit Rules

Defining Last-Resort Default Rules
==================================

   You can define a last-resort implicit rule by writing a terminal
match-anything pattern rule with no dependencies (*note Match-Anything
Rules::.).  This is just like any other pattern rule; the only thing
special about it is that it will match any target.  So such a rule's
commands are used for all targets and dependencies that have no commands
of their own and for which no other implicit rule applies.

   For example, when testing a makefile, you might not care if the
source files contain real data, only that they exist.  Then you might
do this:

     %::
             touch $@

to cause all the source files needed (as dependencies) to be created
automatically.

   You can instead define commands to be used for targets for which
there are no rules at all, even ones which don't specify commands.  You
do this by writing a rule for the target `.DEFAULT'.  Such a rule's
commands are used for all dependencies which do not appear as targets in
any explicit rule, and for which no implicit rule applies.  Naturally,
there is no `.DEFAULT' rule unless you write one.

   If you use `.DEFAULT' with no commands or dependencies:

     .DEFAULT:

the commands previously stored for `.DEFAULT' are cleared.  Then `make'
acts as if you had never defined `.DEFAULT' at all.

   If you do not want a target to get the commands from a match-anything
pattern rule or `.DEFAULT', but you also do not want any commands to be
run for the target, you can give it empty commands (*note Defining
Empty Commands: Empty Commands.).

   You can use a last-resort rule to override part of another makefile.
*Note Overriding Part of Another Makefile: Overriding Makefiles.