.\" @(#)diff.1 1.1 94/10/31 SMI; from UCB 4.3 BSD and S5R2 6.2
.TH DIFF 1 "2 October 1989"
.SH NAME
diff \- display line-by-line differences between pairs of text files
.SH SYNOPSIS
.B diff
[
.B \-bitw
]
[
.B \-c
[
.I #
] |
.B \-e
|
.B \-f
|
.B \-n
|
.B \-h
] 
.I "\0filename1 filename2"
.br
.B diff
[
.B \-bitw
] [
.BI \-D string
] 
.I "\0filename1 filename2"
.br
.B diff
[
.B \-bitw
] [
.B \-c
[
.I #
] | 
.B \-e
| 
.B \-f
|
.B \-n
|
.B \-h
] [
.B \-l
] [
.B \-r
] [
.B \-s
] [
.BI \-S name
] 
.I "\0directory1 directory2"
.SH DESCRIPTION
.IX "diff command"  ""  "\fLdiff\fP \(em differential compare"
.IX files  "differential compare"
.IX files  "find differences"
.IX directory  "differential compare"
.IX compare  "files differentially"
.LP
.B diff
is a
.I differential
file comparator.  When run
on regular files, and when
comparing text files that differ during directory comparison (see the
notes below on comparing directories),
.B diff
tells what lines must be changed in the
files to bring them into agreement.
Except in rare circumstances,
.B diff
finds a smallest sufficient set of differences.  If neither
.I filename1
nor
.I filename2
is a directory, either may be given as 
.RB ` \- ',
in which case the standard input is used.  If
.I filename1
is a directory,
a file in that directory whose filename is
the same as the filename of
.I filename2
is used (and vice versa).
.LP
There are several options for output format;
the default output format contains lines of these forms:
.IP "" 5
.I n\|1
.B a
.IR n\|3 , \|n\|4
.br
.IR n\|1 , \|n\|2
.B d
.I n\|3
.br
.IR n\|1 , \|n\|2
.B c
.IR n\|3 , \|n\|4
.LP
These lines resemble
.BR ed (1)
commands to convert
.I filename1
into
.IR filename2 .
The numbers after the letters pertain to
.IR filename2 .
In fact, by exchanging
.B a
for
.B d
and reading backward
one may ascertain equally how to convert 
.I filename2
into
.IR filename1 .
As in 
.BR ed (1),
identical pairs, where
.I n\|1
=
.I n\|2
or
.I n\|3
=
.IR n\|4 ,
are abbreviated as a single number.
.LP
Following each of these lines come all the lines that are
affected in the first file flagged by
.RB ` < ', 
then all the lines that are affected in the second file
flagged by
.RB ` > '.
.LP
If both arguments are directories,
.B diff
sorts the contents of the directories
by name, and then runs the regular file
.B diff
program as described above on text files which are different.
Binary files which differ, common
subdirectories, and files which appear
in only one directory are listed.
.SH OPTIONS
.TP
.B \-b
Ignore trailing blanks (\s-1SPACE\s0 and
.SM TAB
characters)
and treat all other strings of blanks as equivalent.
.TP
.B \-i
Ignore the case of letters; for example,
.RB ` A '
will compare equal to
.RB ` a '.
.TP
.B \-t
Expand
.SM TAB
characters in output lines.  Normal or
.B \-c
output adds character(s) to the front of each line which may alter
the indentation of the original source
lines and make the output listing
difficult to interpret.  This option will
preserve the original source's indentation.
.TP
.B \-w
Ignore all blanks (\s-1SPACE\s0 and
.SM TAB
characters); for example,
.RB ` "if\ (\ a\ =\|=\ b\ )" '
will compare equal to
.RB ` if(a=\|=b) '.
.LP
The following four options are mutually exclusive:
.TP
.BR \-c [\fI#\fP]
Produce a listing of differences with lines of context.
The default is to present 3 lines of context
and may be changed, (to 10, for example), by
.BR \-c10 \&.
With
.B \-c
the output format is modified slightly:  output begins with
identification of the files involved and their creation dates, then
each change is separated by a line with a dozen
.BR * \|s.
The lines removed from
.I filename1
are marked with
.RB ` "\(mi " ';
those added to
.I filename2
are marked
.RB ` "+ " '.
Lines which are changed from one
file to the other are marked in both files with
.RB ` "! " '.
.IP
Changes which lie within <context> lines of each other are grouped
together on output.  This is a change from the previous 
.RB ` "diff \-c" '
but the resulting output is usually much easier to interpret.
.TP
.B \-e
Produce a script of
.BR a ,
.BR c ,
and 
.B d
commands for the editor
.BR ed ,
which will recreate
.I filename2
from
.IR filename1 .
.br
.ne 5
.IP
In connection with
.BR \-e ,
the following shell program may help
maintain multiple versions of a file.
Only an ancestral file ($1) and a chain of version-to-version
.B ed
scripts ($2,\|$3,\|.\|.\|.) made by
.B diff
need be on hand.
A `latest version' appears on the standard output.
.sp .5
.RS
.RS
.B "(shift; cat $*; echo \'1,$p\') \(bv ed \- $1"
.RE
.RE
.IP
Extra commands are added to the output
when comparing directories with
.BR \-e ,
so that the result is a
.BR sh
script for converting text files
which are common to the two directories
from their state in
.I directory1
to their state in
.IR directory2 .
.TP
.B \-f
Produce a script similar to that of
.B \-e,
not useful with
.BR ed ,
which is in the opposite order.
.TP
.B \-n
Produce a script similar to that of
.BR \-e ,
but in the opposite order and with a count of changed lines on each
insert or delete command.
.TP
.B \-h
Do a fast, half-hearted job.
It works only when changed stretches are short and well separated,
but does work on files of unlimited length.
.LP
Options for the second form of 
.B diff
are as follows:
.TP
.BI \-D string
Create a merged version of
.I filename1
and
.I filename2
on the standard output, with C preprocessor controls included so that
a compilation of the result without defining 
.I string
is equivalent
to compiling
.IR filename1 ,
while defining
.I string
will yield
.IR filename2 .
.LP
Options when comparing directories are:
.TP
.B \-l
Long output format; each text file
.B diff
is piped through
.BR pr (1V)
to paginate it, other differences are remembered and summarized
after all text file differences are reported.
.TP
.B \-r
Apply
.B diff
recursively to common subdirectories encountered.
.TP
.B \-s
Report files which are the same, which are otherwise not mentioned.
.TP
.BI \-S name
Start a directory
.B diff
in the middle, beginning with file
.IR name .
.SH ENVIRONMENT
.LP
The environment variables
.BR \s-1LC_CTYPE\s0 ,
.BR \s-1LANG\s0 ,
and
.B \s-1LC\s0_default
control the character classification
throughout
.BR diff .
On entry to
.BR diff ,
these environment variables are checked in the
following order:
.BR \s-1LC_CTYPE\s0 ,
.BR \s-1LANG\s0 ,
and
.BR \s-1LC\s0_default.
When a valid value is found,
remaining environment variables for character classification
are ignored.
For example, a new setting for
.B \s-1LANG\s0
does not override the current valid character
classification rules of
.BR \s-1LC_CTYPE\s0 .
When none of the values is valid,
the shell character
classification defaults to the 
.SM POSIX.1 \*(lqC\*(rq
locale.
.SH FILES
.PD 0
.TP 20
.B /tmp/d?????
.TP
.B /usr/lib/diffh
for 
.B \-h
.PD
.SH "SEE ALSO"
.BR cc (1V),
.BR cmp (1),
.BR comm (1),
.BR cpp (1),
.BR diff3 (1V),
.BR ed (1),
.BR pr (1V),
.BR locale (5),
.BR iso_8859_1 (7)
.SH DIAGNOSTICS
.LP
Exit status is 0 for no differences,
1 for some differences, 2 for trouble.
.TP 5
.BI "Missing newline at end of file" X
Indicates that the last line of file
.I X
did not have a
.SM NEWLINE\s0.
If the lines are different, they will be flagged and output,
although the output will seem to indicate they are the same.
.br
.ne 9
.SH BUGS
.LP
Editing scripts produced under the
.B \-e 
or
.B \-f 
option are naive about
creating lines consisting of a single 
.RB ` . '.
.LP
When comparing directories with the
.BR \-b ,
.BR \-w ,
or
.B \-i
options specified,
.B diff
first compares the files (as in 
.BR cmp (1),
and then runs the regular
.B 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 blank string or case differences.
.LP
The 
.B \-D
option ignores existing preprocessor controls in the source
files, and can generate 
.BR #ifdefs 's
with overlapping scope.  The output should be checked by hand,
or run through
.RB ` "cc \-E" '
(see
.BR cc (1V))
and then 
.BR diff ed
with the original source files.  Discrepancies revealed should be
corrected before compilation.