ref: 8589a591dee9ccb46e09fbb5bf6962cabd178f98
dir: /sys/man/1/diff/
.TH DIFF 1 .SH NAME diff \- differential file comparator .SH SYNOPSIS .B diff [ .B -abcefmnrw ] .I file1 ... file2 .SH DESCRIPTION .I 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 .I diff for text files and .IR cmp (1) otherwise. If more than two file names are given, then each argument is compared to the last argument as above. The .B -r option causes .I diff to process similarly named subdirectories recursively. When processing more than one file, .I diff prefixes file differences with a single line listing the two differing files, in the form of a .I diff command line. The .B -m flag causes this behavior even when processing single files. .PP The normal output contains lines of these forms: .IP "" 5 .I n1 .B a .I n3,n4 .br .I n1,n2 .B d .I n3 .br .I n1,n2 .B c .I n3,n4 .PP These lines resemble .I ed commands to convert .I file1 into .IR file2 . The numbers after the letters pertain to .IR file2 . In fact, by exchanging `a' for `d' and reading backward one may ascertain equally how to convert .I file2 into .IR file1 . As in .IR ed , identical pairs where .I n1 = .I n2 or .I n3 = .I n4 are abbreviated as a single number. .PP 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 `>'. .PP The .B -b option causes trailing blanks (spaces and tabs) to be ignored and other strings of blanks to compare equal. The .B -w option causes all white-space to be removed from input lines before applying the difference algorithm. .PP The .B -n option prefixes each range with .IB file : \fR and inserts a space around the .BR a , .BR c , and .B d verbs. The .B -e option produces a script of .I "a, c" and .I d commands for the editor .IR ed , which will recreate .I file2 from .IR file1 . The .B -f option produces a similar script, not useful with .IR ed , in the opposite order. It may, however, be useful as input to a stream-oriented post-processor. .PP The .B -c option includes three lines of context around each change, merging changes whose contexts overlap. In this mode, .I diff prints .L - and .L + instead of .L < and .L > because the former are easier to distinguish when mixed. The .B -a flag displays the entire file as context. .PP Except in rare circumstances, .I diff finds a smallest sufficient set of file differences. .SH FILES .B /tmp/diff[12] .SH SOURCE .B /sys/src/cmd/diff .SH "SEE ALSO" .IR cmp (1), .IR comm (1), .IR ed (1), .IR idiff (1) .SH DIAGNOSTICS Exit status is the empty string for no differences, .L some for some, and .L error for trouble. .SH BUGS Editing scripts produced under the .BR -e " or" .BR -f " option are naive about" creating lines consisting of a single `\fB.\fR'. .PP When running .I diff on directories, the notion of what is a text file is open to debate.