diff(1)

NAME

diff — differential file and directory comparator

SYNOPSIS

diff [-C n] [-S name] [-lrs] [-bcefhintw] dir1 dir2

diff [-C n] [-S name] [-bcefhintw] file1 file2

diff [-D string] [-biw] file1 file2

DESCRIPTION

Comparing Directories

If both arguments are directories, diff sorts the contents of the directories by name, then runs the regular file diff algorithm (described below) on text files that have the same name in each directory but are different. Binary files that differ, common subdirectories, and files that appear in only one directory are listed. When comparing directories, the following options are recognized:

-l: Long output format; each text file diff is piped through pr to paginate it (see pr(1)). Other differences are remembered and summarized after all text file differences are reported.
-r: Applies diff recursively to common subdirectories encountered.
-s: diff reports files that are identical but otherwise not mentioned.
-S name: Starts a directory diff in the middle of the sorted directory, beginning with file name.

Comparing Files

When run on regular files, and when comparing text files that differ during directory comparison, diff tells what lines must be changed in the files to bring them into agreement. diff usually finds a smallest sufficient set of file differences. However, it can be misled by lines containing very few characters or by other situations. If neither file1 nor file2 is a directory, either can be specified as -, in which case the standard input is used. If file1 is a directory, a file in that directory whose filename is the same as the filename of file2 is used (and vice versa).

There are several options for output format. The default output format contains lines resembling the following:

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 backwards 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 >.

Except for -b, -w, -i, or -t which can be given with any of the others, the following options are mutually exclusive:

-e: Produce a script of a, c, and d commands for the ed editor suitable for recreating file2 from file1. Extra commands are added to the output when comparing directories with -e, so that the result is a shell script for converting text files common to the two directories from their state in dir1 to their state in dir2.
-f: Produce a script similar to that of the -e option that is not useful with ed but is more readable by humans.
-n: Produce a script similar to that of -e, but in the opposite order, and with a count of changed lines on each insert or delete command. This is the form used by rcsdiff (see rcsdiff(1)).
-c: Produce a difference list with 3 lines of context. -c modifies the output format slightly: the output begins with identification of the files involved, followed by their creation dates, then each change separated by a line containing about twelve asterisks (*)s. Lines removed from file1 are marked with -, and lines added to file2 are marked +. Lines that change from one file to the other are marked in both files with with !. Changes that lie within 3 lines of each other in the file are grouped together on output.
-C n: Output format similar to -c but with n lines of context.
-h: Do a fast, half-hearted job. This option works only when changed stretches are short and well separated, but can be used on files of unlimited length.
-D string: Create a merged version of file1 and file2 on the standard output, with C preprocessor controls included so that a compilation of the result without defining string is equivalent to compiling file1, while compiling the result with string defined is equivalent to compiling file2.
-b: Ignore trailing white space characters, except newline character and treat other string of blanks as equal. For example, xyz\t\f and xyz are treated as equal.
-w: Ignore all white space characters, except newline character. For example, if ( a == b ) and if(a==b) are treated as equal.
-i: Ignores uppercase/lowercase differences. Thus A is treated the same as a.
-t: Expand tabs in output lines. Normal or -c output adds one or more characters to the front of each line. Resulting misalignment of indentation in the original source lines can make the output listing difficult to interpret. This option preserves original source file indentation.

EXTERNAL INFLUENCES

Environment Variables

LANG determines the locale to use for the locale categories when both LC_ALL and the corresponding environment variable (beginning with LC_) do not specify a locale. If LANG is not set or is set to the empty string, a default of "C" (see lang(5)) is used.

LC_CTYPE determines the space characters for the diff command, and the interpretation of text within file as single- and/or multi-byte characters.

LC_MESSAGES determines the language in which messages are displayed.

If any internationalization variable contains an invalid setting, diff and diffh behave as if all internationalization variables are set to "C". See environ(5).

International Code Set Support

Single- and multi-byte character code sets are supported with the exception that diff and diffh do not recognize multi-byte alternative space characters.

RETURN VALUE

Upon completion, diff returns with one of the following exit values:

0: No differences were found.
1: Differences were found.
>1: An error occurred.

EXAMPLES

The following command creates a script file script:

diff -e x1 x2 >script 

w is added to the end of the script in order to save the file:

echo w >> script 

The script file can then be used to create the file x2 from the file x1 using the editor ed in the following manner:

ed x1 < script 

The following command produces the difference output with 2 lines of context information before and after the line that was different:

diff -C2 x1 x2 

The following command ignores all blanks and tabs and ignores uppercase-lowercase differences.

diff -wi x1 x2 

WARNINGS

Editing scripts produced by the -e or -f option are naive about creating lines consisting of a single dot (.).

When comparing directories with the -b, -w, or -i options specified, diff first compares the files in the same manner as cmp, then runs the diff algorithm if they are not equal. This may cause a small amount of spurious output if the files are identical except for insignificant blank strings or uppercase/lowercase differences.

The default algorithm requires memory allocation of roughly six times the size of the file. If sufficient memory is not available for handling large files, the -h option or bdiff can be used (see bdiff(1)).

With other options if sufficient memory is not available, then either the swap or maxdsiz values can be increased.

When run on directories with the -r option, diff recursively descends sub-trees. When comparing deep multi-level directories, more memory may be required than is currently available on the system. The amount of memory required depends on the depth of recursion and the size of the files.

AUTHOR

diff was developed by AT&T, the University of California, Berkeley, and HP.

FILES

/usr/lbin/diffh: used by -h option

STANDARDS CONFORMANCE

diff: SVID2, SVID3, XPG2, XPG3, XPG4, POSIX.2