NAME

diff − differential file comparator

SYNOPSIS

diff [ −efbh ] file1 file2

DESCRIPTION

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 with the name 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 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 connection with −e, the following shell program may help maintain 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. 

FILES

/tmp/d????? 
/usr/lib/diffh for −h

SEE ALSO

cmp(1), comm(1), ed(1). 

DIAGNOSTICS

Exit status is 0 for no differences, 1 for some differences, 2 for trouble. 

BUGS

Editing scripts produced under the −e or −f option are naive about creating lines consisting of a single period (.). 

May 16, 1980