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