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 numbers after the let-
ters 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 connection with -e, the following shell program may help main-
tain multiple versions of a file. Only an ancestral file ($1) and a chain of version-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 file differences.
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 creating lines consist-
ing of a single `.'.