NAME
diff - differential file comparator
SYNOPSIS
diff [ -acefmnbwr ] 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, similarly 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 compared 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 differences 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.
The -c option includes three lines of context around each change,
merging changes whose contexts overlap. The -a flag displays the
entire file as context.
Except in rare circumstances, diff finds a smallest sufficient set of
file differences.
FILES
/tmp/diff[12]
SOURCE
/src/cmd/diff
SEE ALSO
cmp(1), comm(1), ed(1)
DIAGNOSTICS
Exit status is the empty string for no differences, for some, and 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.
DIFF(1)