DIFF(1) OpenBSD Reference Manual DIFF(1)
diff - differential file and directory comparator
diff [-abdilpTtw] [-c | -e | -f | -n | -q | -u] [-I pattern] [-L label]
diff [-abdilpTtw] [-I pattern] [-L label] -C number file1 file2
diff [-abdiltw] [-I pattern] -D string file1 file2
diff [-abdilpTtw] [-I pattern] [-L label] -U number file1 file2
diff [-abdilNPprsTtw] [-c | -e | -f | -n | -q | -u] [-I pattern]
[-L label] [-S name] [-X file] [-x pattern] dir1 dir2
The diff utility compares the contents of file1 and file2 and writes to
the standard output the list of changes necessary to convert one file
into the other. No output is produced if the files are identical.
Output options (mutually exclusive):
Like -c but produces a diff with number lines of context.
-c Produces a diff with 3 lines of context. With -c the output
format is modified slightly: the output begins with
identification of the files involved and their creation dates and
then each change is separated by a line with fifteen *'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 `! '. Changes which lie
within 3 lines of each other are grouped together on output.
Creates 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 output in a form suitable as input for the editor
utility, ed(1), which can then be used to convert file1 into
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 Identical output to that of the -e flag, but in reverse order.
It cannot be digested by ed(1).
-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. This is the form used by rcsdiff(1).
-q Just print a line when the files differ. Does not output a list
Like -u but produces a diff with number lines of context.
-u Produces a unified diff with 3 lines of context. A unified diff
is similar to the context diff produced by the -c option.
However, unlike with -c, all lines to be changed (added and/or
removed) are present in a single section.
-a Treat all files as ASCII text. Normally diff will simply print
``Binary files ... differ'' if files contain binary characters.
Use of this option forces diff to produce a diff.
-b Causes trailing blanks (spaces and tabs) to be ignored, and other
strings of blanks to compare equal.
-d Try very hard to produce a diff as small as possible. This may
consume a lot of processing power and memory when processing
large files with many changes.
Ignores changes, insertions, and deletions whose lines match the
extended regular expression pattern. Multiple -I patterns may be
specified. All lines in the change must match some pattern for
the change to be ignored. See re_format(7) for more information
on regular expression patterns.
-i Ignores the case of letters. E.g., ``A'' will compare equal to
Print label instead of the first (and second, if this option is
specified twice) file name and time in the context or unified
-l Long output format; each text file diff'd is piped through pr(1)
to paginate it; other differences are remembered and summarized
after all text file differences are reported.
-p With unified and context diffs, show with each change the first
40 characters of the last line before the context beginning with
a letter, an underscore or a dollar sign. For C source code
following standard layout conventions, this will show the
prototype of the function the change applies to.
-T Print a tab rather than a space before the rest of the line for
the normal, context or unified output formats. This makes the
alignment of tabs in the line consistent.
-t Will expand tabs in output lines. Normal or -c 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 (blanks and tabs) to be
totally ignored. E.g., ``if ( a == b )'' will compare equal to
Directory comparison options:
-N If a file is found in only one directory, act as if it was found
in the other directory too but was of zero size.
-P If a file is found only in dir2, act as if it was found in dir1
too but was of zero size.
-r Causes application of diff recursively to common subdirectories
Re-starts a directory diff in the middle, beginning with file
-s Causes diff to report files which are the same, which are
otherwise not mentioned.
Exclude files and subdirectories from comparison whose basenames
match lines in file. Multiple -X options may be specified.
Exclude files and subdirectories from comparison whose basenames
match pattern. Patterns are matched using shell-style globbing
via fnmatch(3). Multiple -x options may be specified.
If both arguments are directories, diff sorts the contents of the
directories by name, and then runs the regular file diff algorithm,
producing a change list, on text files which are different. Binary files
which differ, common subdirectories, and files which appear in only one
directory are described as such. In directory mode only regular files
and directories are compared. If a non-regular file such as a device
special file or FIFO is encountered, a diagnostic message is printed.
If only one of file1 and file2 is a directory, diff is applied to the
non-directory file and the file contained in the directory file with a
filename that is the same as the last component of the non-directory
If either file1 or file2 is `-', the standard input is used in its place.
The default (without -e, -c, or -n options) output contains lines of
these forms, where XX, YY, ZZ, QQ are line numbers respective of file
XXaYY At (the end of) line XX of file1, append the contents of
line YY of file2 to make them equal.
XXaYY,ZZ Same as above, but append the range of lines, YY through ZZ
of file2 to line XX of file1.
XXdYY At line XX delete the line. The value YY tells to which
line the change would bring file1 in line with file1.
XX,YYdZZ Delete the range of lines XX through YY in file1.
XXcYY Change the line XX in file1 to the line YY in file2.
XX,YYcZZ Replace the range of specified lines with the line ZZ.
XX,YYcZZ,QQ Replace the range XX,YY from file1 with the range ZZ,QQ from
These lines resemble ed(1) subcommands to convert file1 into file2. The
line numbers before the action letters pertain to file1; those after
pertain to file2. Thus, by exchanging a for d and reading the line in
reverse order, one can also determine how to convert file2 into file1.
As in ed(1), identical pairs (where num1 = num2) are abbreviated as a
TMPDIR If the environment variable TMPDIR exists, diff will use the
directory specified by TMPDIR as the temporary directory.
/tmp/diff.XXXXXXXX Temporary file used when comparing a device or the
standard input. Note that the temporary file is
unlinked as soon as it is created so it will not show
up in a directory listing.
The diff utility exits with one of the following values:
0 No differences were found.
1 Differences were found.
>1 An error occurred.
cmp(1), comm(1), diff3(1), ed(1), patch(1), sdiff(1)
James W. Hunt and M. Douglas McIlroy, "An Algorithm for Differential File
Comparison", Computing Science Technical Report, Bell Laboratories 41,
The diff utility is compliant with the IEEE Std 1003.1-2008 (``POSIX.1'')
The flags [-aDdIiLlNnPpqSsTtwXx] are extensions to that specification.
A diff command appeared in Version 6 AT&T UNIX.
When comparing directories with the -b, -w or -i options specified, diff
first compares the files ala cmp(1), 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 whitespace or case differences.
OpenBSD 5.1 February 3, 2011 OpenBSD 5.1
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