NAME

diff − differential file comparator

SYNOPSIS

­diff [ ­−efbwr ] 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 recursively process similarly named subdirectories.  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 ­−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. 

Except in rare circumstances, ­diff finds a smallest sufficient set of file differences. 

FILES

/tmp/diff[12]

SEE ALSO

cmp(1), ed(1)

DIAGNOSTICS

Exit status is ­empty for no differences, ­some for some, and ­error 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. 

Plan 9  —  January 03, 1993