NAME

diff − show differences between the contents of files or directories

SYNOPSIS

diff [ −b ] [ −c[#] | e | f | h ]  filename1 filename2
diff [ −b ] [ −Dstring ]  filename1 filename2
diff [ −b ] [ −c[#] | e | f | h ] [ −l ] [ −r ] [ −s ] [ −Sname ]  dir1 dir2

DESCRIPTION

diff is a differential file comparator.  When run on regular files, and when comparing text files that differ during directory comparison (see the notes below on comparing directories), diff tells what lines must be changed in the files to bring them into agreement.  Except in rare circumstances, diff finds a smallest sufficient set of differences.  If neither filename1 nor filename2 is a directory, either may be given as ‘−’, in which case the standard input is used.  If filename1 is a directory, a file in that directory whose filename is the same as the filename of filename2 is used (and vice versa). 

There are several options for output format; the default output format 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 ‘>’. 

If both arguments are directories, diff sorts the contents of the directories by name, and then runs the regular file diff program as described above on text files which are different.  Binary files which differ, common subdirectories, and files which appear in only one directory are listed. 

OPTIONS

−bignore trailing blanks (spaces and tabs); other strings of blanks compare equal. 

The following four options are mutually exclusive:

−c[#]produces a diff with lines of context.  The default is to present 3 lines of context and may be changed, (to 10, for example), by −c10.  With −c the 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 which are changed from one file to the other are marked in both files with ‘!’. 

−eproduce 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

Extra commands are added to the output when comparing directories with −e, so that the result is a sh(1) script for converting text files which are common to the two directories from their state in dir1 to their state in dir2. 

−fproduces a script similar to that of −e, not useful with ed, and 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 for the second form of diff are as follows:

−Dstring
create a merged version of filename1 and filename2 on the standard output, 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. 

Options when comparing directories are:

−l long output format; each text file diff is piped through pr to paginate it, other differences are remembered and summarized after all text file differences are reported. 

−r apply diff recursively to common subdirectories encountered. 

−s report files which are the same, which are otherwise not mentioned. 

−Sname
starts a directory diff in the middle, beginning with file name. 

FILES

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

SEE ALSO

cmp(1), cc(1), comm(1), ed(1), diff3(1), cpp(1)

DIAGNOSTICS

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

BUGS

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

When comparing directories with the −b option specified, diff first compares the files (as in cmp), and then runs the regular diff algorithm if they are not equal.  This may cause a small amount of spurious output if the the only differences are in the placement of blank strings. 

The −D option ignores existing preprocessor controls in the source files, and can generate #ifdefs’s with overlapping scope.  The output should be checked by hand, or run through cc −E and then diffed with the original source files.  Discrpancies revealed should be corrected before compilation. 

Sun Release 3.0β  —  Last change: 23 September 1985