DIFF(1) DIFF(1)
NAME
diff - differential file comparator
SYNOPSIS
diff [ -abcefmnruw ] file1 ... file2
DESCRIPTION
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, simi-
larly named files in the two directories are compared by the
method of diff for text files and cmp(1) otherwise. If more
than two file names are given, then each argument is com-
pared to the last argument as above. The -r option causes
diff to process similarly named subdirectories recursively.
When processing more than one file, diff prefixes file dif-
ferences with a single line listing the two differing files,
in the form of a diff command line. The -m flag causes this
behavior even when processing single files.
The normal output contains lines of these forms:
n1 a n3,n4
n1,n2 d n3
n1,n2 c n3,n4
These lines resemble ed commands to convert file1 into
file2. The numbers after the letters pertain to file2. In
fact, by exchanging `a' for `d' and reading backward one may
ascertain equally how to convert file2 into file1. As in ed,
identical pairs where n1 = n2 or n3 = n4 are abbreviated as
a single number.
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 `>'.
The -b option causes trailing blanks (spaces and tabs) to be
ignored and other strings of blanks to compare equal. The
-w option causes all white-space to be removed from input
lines before applying the difference algorithm.
The -n option prefixes each range with file: and inserts a
space around the a, c, and d verbs. The -e option produces
a script of a, c and d commands for the editor ed, which
will recreate file2 from file1. The -f option produces a
similar script, not useful with ed, in the opposite order.
It may, however, be useful as input to a stream-oriented
post-processor.
Page 1 Plan 9 (printed 11/22/24)
DIFF(1) DIFF(1)
The -c option includes three lines of context around each
change, merging changes whose contexts overlap. In this
mode, diff prints `-' and `+' instead of `<' and `>' because
the former are easier to distinguish when mixed. The -a
flag displays the entire file as context.
The -u option provides a unix-compatible unified diff. This
format is similar to that provided by -c. However, the `+'
and `-' prefixes are not separated from the rest of the line
by spaces, and the file header is in the following format:
--- filename.old
+++ filename.new
@@ -line,len +line,len @@
Except in rare circumstances, diff finds a smallest suffi-
cient set of file differences.
FILES
/tmp/diff[12]
SOURCE
/sys/src/cmd/diff
SEE ALSO
cmp(1), comm(1), ed(1), idiff(1)
DIAGNOSTICS
Exit status is the empty string for no differences, `some'
for some, and `error' for trouble.
BUGS
Editing scripts produced under the -e or -f option are naive
about creating lines consisting of a single `.'.
When running diff on directories, the notion of what is a
text file is open to debate.
Page 2 Plan 9 (printed 11/22/24)