DIFF(I) 5/15/74 DIFF(I) NAME diff - differential file comparator SYNOPSIS diff [ - ] name1 name2 DESCRIPTION Diff tells what lines must be changed in two files to bring them into agreement. 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 file name1 into file name2. The numbers after the letters pertain to file name2. In fact, by exchanging `a' for `d' and reading backward one may ascertain equally how to convert file name2 into name1. 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 `.'. Under the
-option, the output of diff is a script of a, c and d commands for the editor ed, which will change the contents of the first file into the contents of the second. In this connection, 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. (cat $2 ... $9; echo "1,$p") | ed - $1 Except for occasional `jackpots', diff finds a smallest sufficient set of file differences. SEE ALSO cmp (I), comm (I), ed (I) DIAGNOSTICS `jackpot' - To speed things up, the program uses hashing. You have stumbled on a case where there is a chance that this has resulted in a difference being called where none actually existed. Sometimes reversing the order of files will make a jackpot go away. BUGS Editing scripts produced under the -option are naive about creating lines consisting of a single `.'.