DIFF(1) General Commands Manual DIFF(1)
diff - differential file comparator
diff [ -efbh ] file1 file2
Diff tells what lines must be changed in two files to bring them into
agreement. If file1 (file2) is `-', the standard input is used. If
file1 (file2) is a directory, then a file in that directory whose file-
name is the same as the file-name of file2 (file1) is used. 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 num-
bers 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 -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. In connec-
tion with -e, the following shell program may help maintain multiple
versions of a file. Only an ancestral file ($1) and a chain of ver-
sion-to-version ed scripts ($2,$3,...) made by diff need be on hand. A
`latest version' appears on the standard output.
(shift; cat $*; echo '1,$p') | ed - $1
Except in rare circumstances, diff finds a smallest sufficient set of
Option -h does a fast, half-hearted job. It works only when changed
stretches are short and well separated, but does work on files of
unlimited length. Options -e and -f are unavailable with -h.
/usr/lib/diffh for -h
cmp(1), comm(1), ed(1)
Exit status is 0 for no differences, 1 for some, 2 for trouble.
Editing scripts produced under the -e or -f option are naive about cre-
ating lines consisting of a single `.'.