DIFF(1)

NAME
diff - differential file comparator

SYNOPSIS

diff [-abitw] [-cefhnu] [-C number] [-U number] file1 file2

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

diff [-abiNtw] [-lrs] [-cefhnu] [-C number] [-S name] [-U number] [-x pattern] directory1 directory2

DESCRIPTION
Diff tells what lines must be changed in two files to bring them into agreement. If file1 (file2) is `-', the standard input is used. If file1 (file2) is a directory, then a file in that directory whose file-name is the same as the file-name of file2 (file1) 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 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 `>'.

-a  causes a list of differences to be output for all files, even for those found to have binary content.

-b  causes trailing whitespace characters to be ignored, and other strings of whitespace to compare equal.

-i  ignores the case of letters. E.g., ``A'' will compare equal to ``a''.

-t  will expand tabs in output lines. Normal, -c or -u output adds character(s) to the front of each line which may screw up the indentation of the original source lines and make the output listing difficult to interpret. This option will preserve the original source's indentation.

-w  is similar to -b but causes whitespace characters to be totally ignored. E.g., ``if ( a == b )'' will compare equal to ``if(a==b)''.

The following options are mutually exclusive:

-c  produces a diff with three lines of context. With -c the output format is modified slightly: the output beginning with identification of the files involved and their creation dates and then each change is separated by a line with a dozen *'s. The lines removed from file1 are marked with `- '; those added to file2 are marked `+ '. Lines which are changed from one file to the other are marked in both files with with `! '.

-C number
    Same as -c but uses number of lines of context.

-D string
    causes diff to 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 defining string will yield file2.

-e  produces a script of a, c and d commands for the editor ed, which will recreate file2 from file1. 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.

-f  produces 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.

-n  produces 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.

-u  produces a unified diff with three lines of context. The output begins with identification of the files involved and their creation dates, followed by the changes separated by `@@ -range +range @@'. Lines removed from file1 are marked with `-', those added to file2 are marked `+'.

-U number
    Same as -u but uses number of lines of context.

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

Options when comparing directories are:

-l  long output format; each text file diff is piped through pr(1) to paginate it, other differences are remembered and summarized after all text file differences are reported.

-N  causes the text of files that exist in one directory only to be output as if compared to an empty file modified at 1/1/70.

-r  causes application of diff recursively to common subdirectories encountered.

-s  causes diff to report files which are the same, which are otherwise not mentioned.

-S name
    starts a directory diff in the middle beginning with file name.

-x pattern
    excludes all file names that match pattern (as described in glob(7)) from comparison. If pattern matches a directory, files below that directory are also excluded.

ENVIRONMENT VARIABLES

LANG, LC_ALL
    See locale(7).

LC_CTYPE
    Sets the mapping of bytes to characters, character case translation and the set of whitespace characters.

SYSV3
    If this variable is set, invalid options are ignored instead of being rejected, and the text of some diagnostic messages is changed.

FILES
/tmp/d?????
/usr/local/heirloom/usr/5lib/diffh    for -h
diff    for directory diffs
pr

SEE ALSO
cmp(1), cc(1), comm(1), ed(1), diff3(1), patch(1), locale(7)

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

NOTES
Editing scripts produced under the -e or -f option are naive about creating lines consisting of a single `.'.

When comparing directories with the -b, -w or -i options specified, diff first compares the files ala cmp, and then decides to run the diff algorithm if they are not equal. This may cause a small amount of spurious output if the files then turn out to be identical because the only differences are insignificant blank string or case differences.

When diff output is used with ed(1) or patch(1) for file synchronization, it is recommended that it is run in the C or another single-byte LC_CTYPE locale since character-to-byte conversion might otherwise hide some changes.