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UNIX in a Nutshell: System V Edition

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UNIX Commands
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diff

diff [options] [diroptions] file1 file2

diff reports lines that differ between file1 and file2. Output consists of lines of context from each file, with file1 text flagged by a < symbol and file2 text, by a > symbol. Context lines are preceded by the ed command (a, c, or d) that would be used to convert file1 to file2. If one of the files is -, standard input is read. If one of the files is a directory, diff locates the filename in that directory corresponding to the other argument (e.g., diff my_dir junk is the same as diff my_dir/junk junk). If both arguments are directories, diff reports lines that differ between all pairs of files having equivalent names (e.g., olddir/program and newdir/program); in addition, diff lists filenames unique to one directory, as well as subdirectories common to both. See also sdiff and cmp.

Options

-b

Ignore repeating blanks and end-of-line blanks; treat successive blanks as one.

-c

Produce output in alternate format, with three lines of context.

-Cn

Like -c, but produce n lines of context.

-cn

Produce n lines of context (default is 3).

-D def

Merge file1 and file2 into a single file containing conditional C preprocessor directives (#ifdef). Defining def and then compiling will yield file2; compiling without defining def yields file1.

-e

Produce a script of commands (a, c, d) to recreate file2 from file1 using the ed editor.

-f

Produce a script to recreate file1 from file2; the script is in the opposite order, so it isn't useful to ed.

-h

Do a half-hearted comparison; complex differences (e.g., long stretches of many changes) may not show up; -e and -f are disabled.

-i

Ignore uppercase and lowercase distinctions.

-n

Like -f, but counts changed lines. rcsdiff works this way.

-t

Expand tabs in output lines; useful for preserving indentation changed by -c format.

-w

Like -b but ignores all spaces and tabs; e.g., a + b is the same as a+b.

Options -c, -C, -D, -e, -f, -h, and -n cannot be combined with each other (they are mutually exclusive). The following diroptions are valid only when both file arguments are directories.

Diroptions

-l

Long format; output is paginated by pr so that diff listings for each file begin on a new page; other comparisons are listed afterward.

-r

Run diff recursively for files in common subdirectories.

-s

Report files that are identical.

-Sfile

Begin directory comparisons with file, skipping files whose names are alphabetically before file.


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