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.TH DIFF 1
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.SH NAME
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diff \- differential file comparator
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.SH SYNOPSIS
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.B diff
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[
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.B -abcefmnrw
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]
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.I file1 ... file2
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.SH DESCRIPTION
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.I Diff
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tells what lines must be changed in two files to bring them
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into agreement.
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If one file
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is a directory,
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then a file in that directory with basename the same as that of
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the other file is used.
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If both files are directories, similarly named files in the
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two directories are compared by the method of
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.I diff
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for text
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files and
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.IR cmp (1)
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otherwise.
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If more than two file names are given, then each argument is compared
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to the last argument as above.
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The
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.B -r
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option causes
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.I diff
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to process similarly named subdirectories recursively.
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When processing more than one file,
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.I diff
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prefixes file differences with a single line
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listing the two differing files, in the form of
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a
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.I diff
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command line.
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The
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.B -m
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flag causes this behavior even when processing single files.
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.PP
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The normal output contains lines of these forms:
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.IP "" 5
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.I n1
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.B a
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.I n3,n4
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.br
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.I n1,n2
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.B d
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.I n3
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.br
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.I n1,n2
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.B c
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.I n3,n4
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.PP
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These lines resemble
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.I ed
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commands to convert
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.I file1
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into
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.IR file2 .
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The numbers after the letters pertain to
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.IR file2 .
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In fact, by exchanging `a' for `d' and reading backward
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one may ascertain equally how to convert
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.I file2
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into
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.IR file1 .
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As in
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.IR ed ,
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identical pairs where
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.I n1
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=
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.I n2
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or
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.I n3
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=
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.I n4
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are abbreviated as a single number.
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.PP
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Following each of these lines come all the lines that are
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affected in the first file flagged by `<',
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then all the lines that are affected in the second file
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flagged by `>'.
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.PP
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The
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.B -b
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option causes
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trailing blanks (spaces and tabs) to be ignored
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and other strings of blanks to compare equal.
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The
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.B -w
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option causes all white-space to be removed from input lines
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before applying the difference algorithm.
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.PP
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The
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.B -n
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option prefixes each range with
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.IB file : \fR
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and inserts a space around the
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.BR a ,
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.BR c ,
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and
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.B d
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verbs.
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The
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.B -e
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option produces a script of
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.I "a, c"
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and
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.I d
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commands for the editor
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.IR ed ,
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which will recreate
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.I file2
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from
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.IR file1 .
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The
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.B -f
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option produces a similar script,
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not useful with
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.IR ed ,
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in the opposite order. It may, however, be
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useful as input to a stream-oriented post-processor.
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.PP
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The
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.B -c
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option includes three lines of context around each
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change, merging changes whose contexts overlap.
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In this mode,
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.I diff
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prints
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.L -
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and
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.L +
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instead of
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.L <
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and
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.L >
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because the former are easier to distinguish when mixed.
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The
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.B -a
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flag displays the entire file as context.
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.PP
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Except in rare circumstances,
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.I diff
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finds a smallest sufficient set of file
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differences.
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.SH FILES
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.B /tmp/diff[12]
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.SH SOURCE
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.B /sys/src/cmd/diff
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.SH "SEE ALSO"
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.IR cmp (1),
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.IR comm (1),
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.IR ed (1),
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.IR idiff (1)
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.SH DIAGNOSTICS
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Exit status is the empty string
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for no differences,
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.L some
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for some,
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and
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.L error
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for trouble.
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.SH BUGS
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Editing scripts produced under the
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.BR -e " or"
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.BR -f " option are naive about"
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creating lines consisting of a single `\fB.\fR'.
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.PP
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When running
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.I diff
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on directories, the notion of what is a text
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file is open to debate.