.\" Copyright (c) 1980, 1990 The Regents of the University of California.
.\" All rights reserved.
.\"
.\" %sccs.include.redist.roff%
.\"
.\"     @(#)diff.1	6.8 (Berkeley) 10/13/91
.\"
.Dd 
.Dt DIFF 1
.Os BSD 4
.Sh NAME
.Nm diff
.Nd differential file and directory comparator
.Sh SYNOPSIS
.Nm diff
.Op Fl cefhn
.Op Fl biwt
.Ar file1 file2
.Nm diff
.Op Fl D Ns Ar string
.Op Fl biw
.Ar file1 file2
.Nm diff
.Op Fl l
.Op Fl r
.Op Fl s
.Op Fl cefhn
.Op Fl biwt
.Op Fl S Ns Ar name
.Ar dir1 dir2
.Sh DESCRIPTION
The
.Nm diff
utility compares the contents of
.Ar file1
and
.Ar file2
and writes to the standard output the list of changes necessary to
convert one file into the other.
No output is produced if the files are identical.
.Pp
Output options (mutually exclusive):
.Bl -tag -width Ds
.It Fl c
produces a diff with lines of context.
The default is to present 3 lines of context and may be changed, e.g to 10, by
.Fl c10 .
With
.Fl c
the output format is modified slightly:
the output beginning with identification of the files involved and
their creation dates and then each change is separated
by a line with a dozen *'s.
The lines removed from
.Ar file1
are marked with `\(mi '; those added to
.Ar file2
are marked `+ '.  Lines which are changed from one
file to the other are marked in both files with with `! '.
Changes which lie within <context> lines of each other are grouped
together on output.  (This is a change from the previous ``diff -c''
but the resulting output is usually much easier to interpret.)
.It Fl e
produces output in a form suitable as input for the editor utility,
.Xr ed 1 ,
which can then be used to convert file1 into file2.
.Pp
Extra commands are added to the output when comparing directories with
.Fl e ,
so that the result is a
.Xr sh  1
script for converting text files which are common to the two directories
from their state in
.Ar dir1
to their state in
.Ar dir2 .
.It Fl f
identical output of the
.Fl e
flag, but in reverse order.  It cannot
be digested by
.Xr ed 1 .
.It Fl h
Invokes an alternate algorithm which can handle files of very long lengths.
There is a trade off. The algorithm can only deal with changes which are
clearly delimited and brief. Long sections of changes and overlaps will
confuse it.
.It Fl n
produces a script similar to that of
.Fl e ,
but in the opposite order and with a count of changed lines on each
insert or delete command.  This is the form used by
.Xr rcsdiff  1  .
.It Fl D Ns Ar string
creates a merged version of
.Ar file1
and
.Ar file2
on the standard output, with C preprocessor controls included so that
a compilation of the result without defining
.Ar string
is equivalent
to compiling
.Ar file1 ,
while defining
.Ar string
will yield
.Ar file2 .
.El
.Pp
Comparison options:
.Bl -tag -width Ds
.It Fl b
causes trailing blanks (spaces and tabs) to be ignored, and other
strings of blanks to compare equal.
.It Fl i
ignores the case of letters.  E.g., ``A'' will compare equal to ``a''.
.It Fl t
will expand tabs in output lines.  Normal or
.Fl c
output adds character(s) to the front of each line which may screw up
the indentation of the original source lines and make the output listing
difficult to interpret.  This option will preserve the original source's
indentation.
.It Fl w
is similar to
.Fl b
but causes whitespace (blanks and tabs) to be totally ignored.  E.g.,
``if\ (\ a\ ==\ b\ )'' will compare equal to ``if(a==b)''.
.El
.Pp
Directory comparison options:
.Bl -tag -width Ds
.It Fl l
long output format; each text file
.Nm diff \'d
is piped through
.Xr pr  1
to paginate it,
other differences are remembered and summarized
after all text file differences are reported.
.It Fl r
causes application of
.Nm diff
recursively to common subdirectories encountered.
.It Fl s
causes
.Nm diff
to report files which are the same, which are otherwise not mentioned.
.It Fl S Ns Ar name
re-starts a directory
.Nm diff
in the middle beginning with file
.Ar name .
.El
.Pp
If both arguments are directories,
.Nm diff
sorts the contents of the directories by name, and then runs the
regular file
.Nm diff
algorithm, producing a change list,
on text files which are different.
Binary files which differ,
common subdirectories, and files which appear in only one directory
are described as such.
.Pp
If only one of
.Ar file1
and
.Ar file2
is a directory,
.Nm diff
is applied to the non-directory file and the file contained in
the directory file with a filename that is the same as the
last component of the non-directory file.
.Pp
If either the
.Ar file1
or
.Ar file2
is
.Sq Fl ,
the standard input is
used in its place.
.Ss Output Style
The default (without
.Fl e ,
.Fl c ,
or
.Fl n
.\"  -C
options)
output contains lines of these forms, where
.Va XX , YY , ZZ , QQ
are line numbers respective of file order.
.Pp
.Bl -tag -width "XX,YYcZZ,QQ" -compact
.It Li XX Ns Ic a Ns Li YY
At (the end of) line
.Va XX
of
.Ar file1 ,
append the contents
of line
.Va YY
of
.Ar file2
to make them equal.
.It Li XX Ns Ic a Ns Li YY,ZZ
Same as above, but append the range of lines,
.Va YY
through
.Va ZZ
of
.Ar file2
to line
.Va XX
of file1.
.It Li XX Ns Ic d Ns Li YY
At line
.Va XX
delete
the line. The value
.Va YY
tells to which line the change
would bring
.Ar file1
in line with
.Ar file1 .
.It Li XX,YY Ns Ic d Ns Li ZZ
Delete the range of lines
.Va XX
through
.Va YY
in
.Ar file1 .
.It Li XX Ns Ic c Ns Li YY
Change the line
.Va XX
in
.Ar file1
to the line
.Va YY
in
.Ar file2.
.It Li XX,YY Ns Ic c Ns Li ZZ
Replace the range of specified lines with the line
.Va ZZ .
.It Li XX,YY Ns Ic c Ns Li ZZ,QQ
Replace the range
.Va XX , Ns YY
from
.Ar file1
with the range
.Va ZZ , Ns QQ
from
.Ar file2 .
.El
.Pp
These lines resemble
.Xr ed 1
subcommands to convert
.Ar file1
into
.Ar file2 .
The line numbers before the action letters pertain to
.Ar file1 ;
those after pertain to
.Ar file2 .
Thus, by exchanging
.Ic a
for
.Ic d
and reading the line in reverse order, one can also
determine how to convert
.Ar file2
into
.Ar file1 .
As in
.Xr ed 1 ,
identical
pairs (where num1 = num2) are abbreviated as a single
number.
.Sh ENVIRONMENT
.Bl -tag -width TMPDIR
.It Ev TMPDIR
If the environment variable
.Ev TMPDIR
exists,
.Nm diff
will use the directory specified by
.Ev TMPDIR
as the temporary directory.
.El
.Sh FILES
.Bl -tag -width /usr/bin/diffh -compact
.It Pa /tmp/d?????
.It Pa /usr/bin/diffh
Alternate algorithm version (used by option
.Fl h ) .
.It Pa /usr/bin/diff
for directory diffs
.It Pa /usr/bin/pr
used by the
.Fl l
option.
.El
.Sh SEE ALSO
.Xr cmp 1 ,
.Xr cc 1 ,
.Xr comm 1 ,
.Xr ed 1 ,
.Xr diff3 1
.Sh DIAGNOSTICS
The
.Nm diff
utility exits with one of the following values:
.Pp
.Bl -tag -width Ds -compact -offset indent
.It \&0
No differences were found.
.It \&1
Differences were found.
.It "\&>\&1"
An error occurred.
.El
.Sh BUGS
The
.Fl f
and
.Fl e
options
do not provide special handling for lines on which the
first and only character is
.Dq Li \&. .
This can cause problems for
.Xr ed 1 .
.Pp
When comparing directories with the
.Fl b ,
.Fl w
or
.Fl i
options specified,
.Nm diff
first compares the files ala
.Ar cmp ,
and then decides to run the
.Nm diff
algorithm if they are not equal.
This may cause a small amount of spurious output if the files
then turn out to be identical because the only differences are
insignificant white space or case differences.
.Sh HISTORY
A
.Nm
command appeared in
.At v6 .