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Manual page for DIFF(1)

diff - display line-by-line differences between pairs of text files

SYNOPSIS

diff [ -bitw ] [ -c [ # ] | -e | -f | -n | -h ] filename1 filename2
diff [ -bitw ] [ -Dstring ] filename1 filename2
diff [ -bitw ] [ -c [ # ] | -e | -f | -n | -h ] [ -l ] [ -r ] [ -s ] [ -Sname ] directory1 directory2

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.1 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.1 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

-b: Ignore trailing blanks (SPACE and TAB characters) and treat all other strings of blanks as equivalent.
-i: Ignore the case of letters; for example, `A' will compare equal to `a'.
-t: Expand TAB characters in output lines. Normal or -c output adds character(s) to the front of each line which may alter 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: Ignore all blanks (SPACE and TAB characters); for example, `if ( a == b )' will compare equal to `if(a==b)'.

The following four options are mutually exclusive:

-c[#]: Produce a listing of differences 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 `! '.
: Changes which lie within <context> lines of each other are grouped together on output. This is a change from the previous `diff -c' but the resulting output is usually much easier to interpret.
-e: Produce 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 script for converting text files which are common to the two directories from their state in directory1 to their state in directory2.
-f: Produce a script similar to that of -e, not useful with ed, which is in the opposite order.
-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.
-h: Do 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.1v 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: Start a directory diff in the middle, beginning with file name.

ENVIRONMENT

The environment variables LC_CTYPE, LANG, and LC_default control the character classification throughout diff. On entry to diff, these environment variables are checked in the following order: LC_CTYPE, LANG, and LC_default. When a valid value is found, remaining environment variables for character classification are ignored. For example, a new setting for LANG does not override the current valid character classification rules of LC_CTYPE. When none of the values is valid, the shell character classification defaults to the POSIX.1 ``C'' locale.

FILES

/tmp/d?????
/usr/lib/diffh: for -h

DIAGNOSTICS

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

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

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, -w, or -i options specified, diff first compares the files (as in cmp.1 and then runs the regular 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.

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' (see cc.1v and then diffed with the original source files. Discrepancies revealed should be corrected before compilation.