NAME

diff − differential file comparator

SYNOPSIS

diff [ −bitw ] [ −c|−e|−f |−h|−n ] filename1 filename2
diff [ −bitw ] [ −C number ] filename1 filename2
diff [ −bitw ] [ −D string ] filename1 filename2
diff [ −bitw ] [ −c|−e| −f|−h|−n ] [−l] [−r] [−s] [ −S name ] directory1
directory2

DESCRIPTION

diff tells what lines must be changed in two files to bring them into agreement.  If filename1 (filename2) is −, the standard input is used.  If filename1 (filename2) is a directory, then a file in that directory with the name filename2 (filename1) 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 filename1 into filename2. The numbers after the letters pertain to filename2. In fact, by exchanging a for d and reading backward one may ascertain equally how to convert filename2 into filename1. 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 >. 

−b Ignores trailing blanks (spaces and tabs) and treats other strings of blanks as equivalent. 

−i Ignores the case of letters; for example, ‘A’ will compare equal to ‘a’. 

−t Expands TAB characters in output lines.  Normal or −c output adds character(s) to the front of each line that may adversely affect the indentation of the original source lines and make the output lines difficult to interpret.  This option will preserve the original source’s indentation. 

−w Ignores all blanks (SPACE and TAB characters) and treats all other strings of blanks as equivalent; for example, ‘if ( a == b )’ will compare equal to ‘if(a==b)’. 

The following options are mutually exclusive:

−c Produces a listing of differences with three lines of context.  With this option output format is modified slightly: output begins with identification of the files involved and their creation dates, then each change is separated by a line with a dozen ∗’s.  The lines removed from filename1 are marked with ’—’; those added to filename2 are marked ’+’. Lines that are changed from one file to the other are marked in both files with ’!’.

−C number
Produces a listing of differences identical to that produced by −c with number lines of context. 

−e Produces a script of a, c, and d commands for the editor ed, which will recreate filename2 from filename1. 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. 

−f Produces a similar script, not useful with ed, in the opposite order. 

−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. 

−n Produces a script similar to −e, but in the opposite order and with a count of changed lines on each insert or delete command. 

−D string
Creates a merged version of filename1 and filename2 with C preprocessor controls included so that a compilation of the result without defining string is equivalent to compiling filename1, while defining string will yield filename2.

The following options are used for comparing directories:

−l Produce output in long format.  Before the diff, each text file is piped through pr(1) to paginate it.  Other differences are remembered and summarized after all text file differences are reported. 

−r Applies diff recursively to common subdirectories encountered. 

−s Reports files that are the identical; these would not otherwise be mentioned. 

−S name
Starts a directory diff in the middle, beginning with the file name.

FILES

/tmp/d?????
/usr/lib/diffh for −h
/usr/bin/pr

SEE ALSO

bdiff(1), cmp(1), comm(1), ed(1), pr(1)

DIAGNOSTICS

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

NOTES

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

Missing newline at end of file X
indicates that the last line of file X did not have a new-line. If the lines are ­different, they will be flagged and output; although the output will seem to in­dicate they are the same.

  —  Essential Utilities