.TH DIFF 1 "22sep1993" "GNU Tools" "GNU Tools"

.SH NAME

diff \- find differences between two files

.SH SYNOPSIS

.B diff

[options] from-file to-file

.SH DESCRIPTION

In the simplest case, 

.I diff

compares the contents of the two files

.I from-file

and

.IR to-file .

A file name of

.B \-

stands for

text read from the standard input.  As a special case,

.B "diff \- \-"

compares a copy of standard input to itself.

If 

.I from-file

is a directory and

.I to-file

is not,

.I diff

compares the file in

.I from-file

whose file name is that of

.IR to-file ,

and vice versa.  The non-directory file must not be

.BR \- .

If both

.I from-file

and

.I to-file

are directories,

.I diff

compares corresponding files in both directories, in

alphabetical order; this comparison is not recursive unless the

.B \-r

or

.B \-\-recursive

option is given.

.I diff

never

compares the actual contents of a directory as if it were a file.  The

file that is fully specified may not be standard input, because standard

input is nameless and the notion of ``file with the same name'' does not

apply.

.B diff

options begin with

.BR \- ,

so normally

.I from-file

and

.I to-file

may not begin with

.BR \- .

However,

.B \-\-

as an

argument by itself treats the remaining arguments as file names even if

they begin with

.BR \- .

.SS Options

Below is a summary of all of the options that GNU

.I diff

accepts.

Most options have two equivalent names, one of which is a single letter

preceded by

.BR \- ,

and the other of which is a long name preceded by

.BR \-\- .

Multiple single letter options (unless they take an

argument) can be combined into a single command line word:

.B \-ac

is

equivalent to

.BR "\-a \-c" .

Long named options can be abbreviated to

any unique prefix of their name.  Brackets

.RB ( [

and

.BR ] )

indicate that an

option takes an optional argument.

.TP

.BI \- lines

Show

.I lines

(an integer) lines of context.  This option does not

specify an output format by itself; it has no effect unless it is

combined with

.B \-c

or

.BR \-u .

This option is obsolete.  For proper

operation,

.I patch

typically needs at least two lines of context.

.TP

.B \-a

Treat all files as text and compare them line-by-line, even if they

do not seem to be text.

.TP

.B \-b

Ignore changes in amount of white space.

.TP

.B \-B

Ignore changes that just insert or delete blank lines.

.TP

.B \-\-brief

Report only whether the files differ, not the details of the

differences.

.TP

.B \-c

Use the context output format.

.TP

.BI "\-C " lines

.br

.ns

.TP

.BI \-\-context[= lines ]

Use the context output format, showing

.I lines

(an integer) lines of

context, or three if

.I lines

is not given.

For proper operation,

.I patch

typically needs at least two lines of

context.

.TP

.BI \-\-changed\-group\-format= format

Use

.I format

to output a line group containing differing lines from

both files in if-then-else format.

.TP

.B \-d

Change the algorithm to perhaps find a smaller set of changes.  This makes

.I diff

slower (sometimes much slower).

.TP

.BI "\-D " name

Make merged if-then-else format output, conditional on the preprocessor

macro

.IR name .

.TP

.B \-e

.br

.ns

.TP

.B \-\-ed

Make output that is a valid

.I ed

script.

.TP

.BI \-\-exclude= pattern

When comparing directories, ignore files and subdirectories whose basenames

match

.IR pattern .

.TP

.BI \-\-exclude\-from= file

When comparing directories, ignore files and subdirectories whose basenames

match any pattern contained in

.IR file .

.TP

.B \-\-expand\-tabs

Expand tabs to spaces in the output, to preserve the alignment of tabs

in the input files.

.TP

.B \-f

Make output that looks vaguely like an

.I ed

script but has changes

in the order they appear in the file.

.TP

.BI "\-F " regexp

In context and unified format, for each hunk of differences, show some

of the last preceding line that matches

.IR regexp .

.TP

.B \-\-forward\-ed

Make output that looks vaguely like an

.B ed

script but has changes

in the order they appear in the file.

.TP

.B \-h

This option currently has no effect; it is present for Unix

compatibility.

.TP

.B \-H

Use heuristics to speed handling of large files that have numerous

scattered small changes.

.TP

.BI \-\-horizon\-lines= lines

Do not discard the last

.I lines

lines of the common prefix

and the first

.I lines

lines of the common suffix.

.TP

.B \-i

Ignore changes in case; consider upper- and lower-case letters

equivalent.

.TP

.BI "\-I " regexp

Ignore changes that just insert or delete lines that match

.IR regexp .

.TP

.BI \-\-ifdef= name

Make merged if-then-else format output, conditional on the preprocessor

macro

.IR name .

.TP

.B \-\-ignore\-all\-space

Ignore white space when comparing lines.

.TP

.B \-\-ignore\-blank\-lines

Ignore changes that just insert or delete blank lines.

.TP

.B \-\-ignore\-case

Ignore changes in case; consider upper- and lower-case to be the same.

.TP

.BI \-\-ignore\-matching\-lines= regexp

Ignore changes that just insert or delete lines that match

.IR regexp .

.TP

.B \-\-ignore\-space\-change

Ignore changes in amount of white space.

.TP

.B \-\-initial\-tab

Output a tab rather than a space before the text of a line in normal or

context format.  This causes the alignment of tabs in the line to look

normal.

.TP

.B \-l

Pass the output through

.I pr

to paginate it.

.TP

.BI "\-L " label

.br

.ns

.TP

.BI \-\-label= label

Use

.I label

instead of the file name in the context format

and unified format

headers.

.TP

.B \-\-left\-column

Print only the left column of two common lines in side by side format.

.TP

.BI \-\-line\-format= format

Use

.I format

to output all input lines in in-then-else format.

.TP

.B \-\-minimal

Change the algorithm to perhaps find a smaller set of changes.  This

makes

.I diff

slower (sometimes much slower).

.TP

.B \-n

Output RCS-format diffs; like

.B \-f

except that each command

specifies the number of lines affected.

.TP

.B \-N

.br

.ns

.TP

.B \-\-new\-file

In directory comparison, if a file is found in only one directory,

treat it as present but empty in the other directory.

.TP

.BI \-\-new\-group\-format= format

Use

.I format

to output a group of lines taken from just the second

file in if-then-else format.

.TP

.BI \-\-new\-line\-format= format

Use 

.I format

to output a line taken from just the second file in

if-then-else format.

.TP

.BI \-\-old\-group\-format= format

Use

.I format

to output a group of lines taken from just the first

file in if-then-else format.

.TP

.BI \-\-old\-line\-format= format

Use

.I format

to output a line taken from just the first file in

if-then-else format.

.TP

.B \-p

Show which C function each change is in.

.TP

.B \-P

When comparing directories, if a file appears only in the second

directory of the two, treat it as present but empty in the other.

.TP

.B \-\-paginate

Pass the output through

.I pr

to paginate it.

.TP

.B \-q

Report only whether the files differ, not the details of the

differences.

.TP

.B \-r

When comparing directories, recursively compare any subdirectories

found.

.TP

.B \-\-rcs

Output RCS-format diffs; like

.B \-f

except that each command

specifies the number of lines affected.

.TP

.B \-\-recursive

When comparing directories, recursively compare any subdirectories

found.

.TP

.B \-\-report\-identical\-files

.br

.ns

.TP

.B \-s

Report when two files are the same.

.TP

.BI "\-S " file

When comparing directories, start with the file

.IR file .

This is

used for resuming an aborted comparison.

.TP

.BI \-\-from\-file= file

Compare

.I file

to all operands.

.I file

can be a directory.

.TP

.BI \-\-to\-file= file

Compare all operands to

.IR file . " file"

can be a directory.

.TP

.B \-\-sdiff\-merge\-assist

Print extra information to help

.IR sdiff .

.I sdiff

uses this

option when it runs

.IR diff .

This option is not intended for users

to use directly.

.TP

.B \-\-show\-c\-function

Show which C function each change is in.

.TP

.BI \-\-show\-function\-line= regexp

In context and unified format, for each hunk of differences, show some

of the last preceding line that matches

.IR regexp .

.TP

.B \-\-side\-by\-side

Use the side by side output format.

.TP

.B \-\-speed\-large\-files

Use heuristics to speed handling of large files that have numerous

scattered small changes.

.TP

.BI \-\-starting\-file= file

When comparing directories, start with the file

.IR file .

This is

used for resuming an aborted comparison.

.TP

.B \-\-suppress\-common\-lines

Do not print common lines in side by side format.

.TP

.B \-t

Expand tabs to spaces in the output, to preserve the alignment of tabs

in the input files.

.TP

.B \-T

Output a tab rather than a space before the text of a line in normal or

context format.  This causes the alignment of tabs in the line to look

normal.

.TP

.B \-\-text

Treat all files as text and compare them line-by-line, even if they

do not appear to be text.

.TP

.B \-u

Use the unified output format.

.TP

.BI \-\-unchanged\-group\-format= format

Use

.I format

to output a group of common lines taken from both files

in if-then-else format.

.TP

.BI \-\-unchanged\-line\-format= format

Use

.I format

to output a line common to both files in if-then-else

format.

.TP

.B \-\-unidirectional\-new\-file

When comparing directories, if a file appears only in the second

directory of the two, treat it as present but empty in the other.

.TP

.BI "\-U " lines

.br

.ns

.TP

.BI \-\-unified[= lines ]

Use the unified output format, showing

.I lines

(an integer) lines of

context, or three if

.I lines

is not given.

For proper operation,

.I patch

typically needs at least two lines of

context.

.TP

.B \-v

.br

.ns

.TP

.B \-\-version

Output the version number of

.IR diff .

.TP

.B \-w

Ignore white space when comparing lines.

.TP

.BI "\-W " columns

.br

.ns

.TP

.BI \-\-width= columns

Use an output width of

.I columns

in side by side format.

.TP

.BI "\-x " pattern

When comparing directories, ignore files and subdirectories whose basenames

match

.IR pattern .

.TP

.BI "\-X " file

When comparing directories, ignore files and subdirectories whose basenames

match any pattern contained in

.IR file .

.TP

.B \-y

Use the side by side output format.

.SH SEE ALSO

cmp(1), comm(1), diff3(1), ed(1), patch(1), pr(1), sdiff(1).

.SH DIAGNOSTICS

An exit status of 0 means no differences were found, 1 means some

differences were found, and 2 means trouble.