usr.bin/diff/diff.1

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.Dd October 12, 2026
.Dt DIFF 1
.Os
.Sh NAME
.Nm diff
.Nd differential file and directory comparator
.Sh SYNOPSIS
.Nm diff
.Op Fl aBbdipTtw
.Oo
.Fl c | e | f |
.Fl n | q | u | y
.Oc
.Op Fl A Ar algo | Fl -algorithm Ar algo
.Op Fl -brief
.Op Fl -color Ns = Ns Ar when
.Op Fl -changed-group-format Ar GFMT
.Op Fl -ed
.Op Fl -expand-tabs
.Op Fl -forward-ed
.Op Fl -ignore-all-space
.Op Fl -ignore-case
.Op Fl -ignore-space-change
.Op Fl -initial-tab
.Op Fl -minimal
.Op Fl -no-dereference
.Op Fl -no-ignore-file-name-case
.Op Fl -normal
.Op Fl -rcs
.Op Fl -show-c-function
.Op Fl -starting-file
.Op Fl -speed-large-files
.Op Fl -strip-trailing-cr
.Op Fl -tabsize Ar number
.Op Fl -text
.Op Fl -unified
.Op Fl I Ar pattern | Fl -ignore-matching-lines Ar pattern
.Op Fl F Ar pattern | Fl -show-function-line Ar pattern
.Op Fl L Ar label | Fl -label Ar label
.Ar file1 file2
.Nm diff
.Op Fl aBbdilpTtw
.Op Fl A Ar algo | Fl -algorithm Ar algo
.Op Fl I Ar pattern | Fl -ignore-matching-lines Ar pattern
.Op Fl F Ar pattern | Fl -show-function-line Ar pattern
.Op Fl L Ar label | Fl -label Ar label
.Op Fl -brief
.Op Fl -color Ns = Ns Ar when
.Op Fl -changed-group-format Ar GFMT
.Op Fl -ed
.Op Fl -expand-tabs
.Op Fl -forward-ed
.Op Fl -ignore-all-space
.Op Fl -ignore-case
.Op Fl -ignore-space-change
.Op Fl -initial-tab
.Op Fl -minimal
.Op Fl -no-dereference
.Op Fl -no-ignore-file-name-case
.Op Fl -normal
.Op Fl -paginate
.Op Fl -rcs
.Op Fl -show-c-function
.Op Fl -speed-large-files
.Op Fl -starting-file
.Op Fl -strip-trailing-cr
.Op Fl -tabsize Ar number
.Op Fl -text
.Fl C Ar number | Fl -context Ar number
.Ar file1 file2
.Nm diff
.Op Fl aBbdiltw
.Op Fl A Ar algo | Fl -algorithm Ar algo
.Op Fl I Ar pattern | Fl -ignore-matching-lines Ar pattern
.Op Fl -brief
.Op Fl -color Ns = Ns Ar when
.Op Fl -changed-group-format Ar GFMT
.Op Fl -ed
.Op Fl -expand-tabs
.Op Fl -forward-ed
.Op Fl -ignore-all-space
.Op Fl -ignore-case
.Op Fl -ignore-space-change
.Op Fl -initial-tab
.Op Fl -minimal
.Op Fl -no-dereference
.Op Fl -no-ignore-file-name-case
.Op Fl -normal
.Op Fl -paginate
.Op Fl -rcs
.Op Fl -show-c-function
.Op Fl -speed-large-files
.Op Fl -starting-file
.Op Fl -strip-trailing-cr
.Op Fl -tabsize Ar number
.Op Fl -text
.Fl D Ar string | Fl -ifdef Ar string
.Ar file1 file2
.Nm diff
.Op Fl aBbdilpTtw
.Op Fl A Ar algo | Fl -algorithm Ar algo
.Op Fl I Ar pattern | Fl -ignore-matching-lines Ar pattern
.Op Fl F Ar pattern | Fl -show-function-line Ar pattern
.Op Fl L Ar label | Fl -label Ar label
.Op Fl -brief
.Op Fl -color Ns = Ns Ar when
.Op Fl -changed-group-format Ar GFMT
.Op Fl -ed
.Op Fl -expand-tabs
.Op Fl -forward-ed
.Op Fl -ignore-all-space
.Op Fl -ignore-case
.Op Fl -ignore-space-change
.Op Fl -initial-tab
.Op Fl -minimal
.Op Fl -no-dereference
.Op Fl -no-ignore-file-name-case
.Op Fl -normal
.Op Fl -paginate
.Op Fl -rcs
.Op Fl -show-c-function
.Op Fl -speed-large-files
.Op Fl -starting-file
.Op Fl -strip-trailing-cr
.Op Fl -tabsize Ar number
.Op Fl -text
.Fl U Ar number | Fl -unified Ar number
.Ar file1 file2
.Nm diff
.Op Fl aBbdilNPprsTtw
.Oo
.Fl c | e | f |
.Fl n | q | u
.Oc
.Op Fl A Ar algo | Fl -algorithm Ar algo
.Op Fl -brief
.Op Fl -color Ns = Ns Ar when
.Op Fl -changed-group-format Ar GFMT
.Op Fl -context
.Op Fl -ed
.Op Fl -expand-tabs
.Op Fl -forward-ed
.Op Fl -ignore-all-space
.Op Fl -ignore-case
.Op Fl -ignore-space-change
.Op Fl -initial-tab
.Op Fl -minimal
.Op Fl -new-file
.Op Fl -no-dereference
.Op Fl -no-ignore-file-name-case
.Op Fl -normal
.Op Fl -paginate
.Op Fl -rcs
.Op Fl -recursive
.Op Fl -report-identical-files
.Op Fl -show-c-function
.Op Fl -speed-large-files
.Op Fl -strip-trailing-cr
.Op Fl -tabsize Ar number
.Op Fl -text
.Op Fl -unidirectional-new-file
.Op Fl -unified
.Op Fl I Ar pattern | Fl -ignore-matching-lines Ar pattern
.Op Fl F Ar pattern | Fl -show-function-line Ar pattern
.Bk -words
.Op Fl L Ar label | Fl -label Ar label
.Op Fl S Ar name | Fl -starting-file Ar name
.Op Fl X Ar file | Fl -exclude-from Ar file
.Op Fl x Ar pattern | Fl -exclude Ar pattern
.Ek
.Ar dir1 dir2
.Nm diff
.Op Fl aBbditwW
.Op Fl -color Ns = Ns Ar when
.Op Fl -expand-tabs
.Op Fl -ignore-all-space
.Op Fl -ignore-blank-lines
.Op Fl -ignore-case
.Op Fl -minimal
.Op Fl -no-dereference
.Op Fl -no-ignore-file-name-case
.Op Fl -strip-trailing-cr
.Op Fl -suppress-common-lines
.Op Fl -tabsize Ar number
.Op Fl -text
.Op Fl -width
.Fl y | Fl -side-by-side
.Ar file1 file2
.Nm diff
.Op Fl -help
.Op Fl -version
.Sh DESCRIPTION
The
.Nm
utility compares the contents of
.Ar file1
and
.Ar 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.
.Pp
Output options (mutually exclusive):
.Bl -tag -width Ds
.It Fl C Ar number Fl -context Ar number
Like
.Fl c
but produces a diff with
.Ar number
lines of context.
.It Fl c
Produces a diff with 3 lines of context.
With
.Fl 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
.Li * Ns 's .
The lines removed from
.Ar file1
are marked with
.Sq \&-\ \& ;
those added to
.Ar file2
are marked
.Sq +\ \& .
Lines which are changed from one file to the other are marked in
both files with
.Sq !\ \& .
Changes which lie within 3 lines of each other are grouped together on
output.
.It Fl D Ar string Fl -ifdef Ar string
Creates a merged version of
.Ar file1
and
.Ar file2
on the standard output, with C preprocessor controls included so that
a compilation of the result without defining
.Ar string
is equivalent to compiling
.Ar file1 ,
while defining
.Ar string
will yield
.Ar file2 .
.It Fl e -ed
Produces output in a form suitable as input for the editor utility,
.Xr ed 1 ,
which can then be used to convert file1 into file2.
.Pp
Extra commands are added to the output when comparing directories with
.Fl e ,
so that the result is a
.Xr sh 1
script for converting text files which are common to the two directories
from their state in
.Ar dir1
to their state in
.Ar dir2 .
Note that when comparing directories with
.Fl e ,
the resulting file may no longer be interpreted as an
.Xr ed 1
script.
Output is added to indicate which file each set of
.Xr ed 1
commands applies to.
These hunks can be manually extracted to produce an
.Xr ed 1
script, which can also be applied with
.Xr patch 1 .
.It Fl f -forward-ed
Identical output to that of the
.Fl e
flag, but in reverse order.
It cannot be digested by
.Xr ed 1 .
.It Fl -help
This option prints a summary to stdout and exits with status 0.
.It Fl n
Produces a script similar to that of
.Fl 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.
.It Fl q -brief
Just print a line when the files differ.
Does not output a list of changes.
Specify twice
.Pq Fl qq
to output nothing at all, for when you only want to examine the exit code.
.It Fl U Ar number Fl -unified Ar number
Like
.Fl u
but produces a diff with
.Ar number
lines of context.
.It Fl u
Produces a
.Em unified
diff with 3 lines of context.
A unified diff is similar to the context diff produced by the
.Fl c
option.
However, unlike with
.Fl c ,
all lines to be changed (added and/or removed) are present in
a single section.
.It Fl -version
This option prints a version string to stdout and exits with status 0.
.It Fl y Fl -side-by-side
Output in two columns with a marker between them.
The marker can be one
of the following:
.Pp
.Bl -tag -width Ds -offset indent -compact
.It space
Corresponding lines are identical.
.It '|'
Corresponding lines are different.
.It '<'
Files differ and only the first file contains the line.
.It '>'
Files differ and only the second file contains the line.
.El
.El
.Pp
Comparison options:
.Bl -tag -width Ds
.It Fl A Ar algo , Fl -algorithm Ar algo
Configure the algorithm used when comparing files.
.Nm
supports 3 algorithms:
.Pp
.Bl -tag -width Ds -compact
.It Cm myers
The Myers diff algorithm finds the shortest edit which transforms one
input into the other.
It generally runs in O(N+D\(S2) time, requiring O(N) space, where N is
the sum of the lengths of the inputs and D is the length of the
difference between them, with a theoretical O(N\(pcD) worst case.
If it encounters worst-case input, the implementation used by
.Nm
falls back to a less optimal but faster algorithm.
.It Cm patience
The Patience variant of the Myers algorithm attempts to create more
aesthetically pleasing diff output by logically grouping lines.
.It Cm stone
The Stone algorithm (commonly known as Hunt-McIlroy or Hunt-Szymanski)
looks for the longest common subsequence between compared files.
Stone encounters worst case performance when there are long common
subsequences.
In large files this can lead to a significant performance impact.
The Stone algorithm is maintained for compatibility.
.El
.Pp
The
.Nm
utility defaults to the Myers algorithm, but will fall back to the
Stone algorithm if the input or output options are not supported by
the Myers implementation.
.It Fl a -text
Treat all files as ASCII text.
Normally
.Nm
will simply print
.Dq Binary files ... differ
if files contain binary characters.
Use of this option forces
.Nm
to produce a diff.
.It Fl B Fl -ignore-blank-lines
Causes chunks that include only blank lines to be ignored.
.It Fl b -ignore-space-change
Causes trailing blanks (spaces and tabs) to be ignored, and other
strings of blanks to compare equal.
.It Fl -color= Ns Oo Ar when Oc
Color the additions green, and removals red, or the value in the
.Ev DIFFCOLORS
environment variable.
The possible values of
.Ar when
are
.Dq Cm never ,
.Dq Cm always
and
.Dq Cm auto .
.Cm auto
will use color if the output is a tty and the
.Ev COLORTERM
environment variable is set to a non-empty string.
.It Fl d -minimal
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.
.It Fl F Ar pattern , Fl -show-function-line Ar pattern
Like
.Fl p ,
but display the last line that matches provided pattern.
.It Fl I Ar pattern Fl -ignore-matching-lines Ar pattern
Ignores changes, insertions, and deletions whose lines match the
extended regular expression
.Ar pattern .
Multiple
.Fl I
patterns may be specified.
All lines in the change must match some pattern for the change to be
ignored.
See
.Xr re_format 7
for more information on regular expression patterns.
.It Fl i -ignore-case
Ignores the case of letters.
E.g.,
.Dq A
will compare equal to
.Dq a .
.It Fl l -paginate
Pass the output through
.Xr pr 1
to paginate it.
.It Fl L Ar label Fl -label Ar label
Print
.Ar label
instead of the first (and second, if this option is specified twice)
file name and time in the context or unified diff header.
.It Fl p -show-c-function
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 and Objective-C source code following standard layout conventions, this
will show the prototype of the function the change applies to.
.It Fl T -initial-tab
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.
.It Fl t -expand-tabs
Will expand tabs in output lines.
Normal or
.Fl 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.
.It Fl w -ignore-all-space
Is similar to
.Fl b -ignore-space-change
but causes whitespace (blanks and tabs) to be totally ignored.
E.g.,
.Dq if (\ \&a == b \&)
will compare equal to
.Dq if(a==b) .
.It Fl W Ar number Fl -width Ar number
Output at most
.Ar number
columns when using side by side format.
The default value is 130.
Note that unless
.Fl t
was specified,
.Nm
will always align the second column to a tab stop, so values of
.Fl -width
smaller than approximately five times the value of
.Fl -tabsize
may yield surprising results.
.It Fl -changed-group-format Ar GFMT
Format input groups in the provided
.Pp
the format is a string with special keywords:
.Bl -tag -width %<
.It %<
lines from FILE1
.It %<
lines from FILE2
.El
.It Fl -ignore-file-name-case
ignore case when comparing file names
.It Fl -no-dereference
do not follow symbolic links
.It Fl -no-ignore-file-name-case
do not ignore case when comparing file names (default)
.It Fl -normal
default diff output
.It Fl -speed-large-files
stub option for compatibility with GNU diff
.It Fl -strip-trailing-cr
strip carriage return on input files
.It Fl -suppress-common-lines
Do not output common lines when using the side by side format
.It Fl -tabsize Ar number
Number of spaces representing a tab (default 8)
.El
.Pp
Directory comparison options:
.Bl -tag -width Ds
.It Fl N -new-file
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.
.It Fl P -unidirectional-new-file
If a file is found only in
.Ar dir2 ,
act as if it was found in
.Ar dir1
too but was of zero size.
.It Fl r -recursive
Causes application of
.Nm
recursively to common subdirectories encountered.
.It Fl S Ar name Fl -starting-file Ar name
Re-starts a directory
.Nm
in the middle, beginning with file
.Ar name .
.It Fl s -report-identical-files
Causes
.Nm
to report files which are the same, which are otherwise not mentioned.
.It Fl X Ar file Fl -exclude-from Ar file
Exclude files and subdirectories from comparison whose basenames match
lines in
.Ar file .
Multiple
.Fl X
options may be specified.
.It Fl x Ar pattern Fl -exclude Ar pattern
Exclude files and subdirectories from comparison whose basenames match
.Ar pattern .
Patterns are matched using shell-style globbing via
.Xr fnmatch 3 .
Multiple
.Fl x
options may be specified.
.El
.Pp
If both arguments are directories,
.Nm
sorts the contents of the directories by name, and then runs the
regular file
.Nm
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.
.Pp
If only one of
.Ar file1
and
.Ar file2
is a directory,
.Nm
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 file.
.Pp
If either
.Ar file1
or
.Ar file2
is
.Sq - ,
the standard input is
used in its place.
.Ss Output Style
The default (without
.Fl e ,
.Fl c ,
or
.Fl n -rcs
.\" -C
options)
output contains lines of these forms, where
.Va XX , YY , ZZ , QQ
are line numbers respective of file order.
.Pp
.Bl -tag -width "XX,YYcZZ,QQ" -compact
.It Li XX Ns Ic a Ns Li YY
At (the end of) line
.Va XX
of
.Ar file1 ,
append the contents
of line
.Va YY
of
.Ar file2
to make them equal.
.It Li XX Ns Ic a Ns Li YY,ZZ
Same as above, but append the range of lines,
.Va YY
through
.Va ZZ
of
.Ar file2
to line
.Va XX
of file1.
.It Li XX Ns Ic d Ns Li YY
At line
.Va XX
delete
the line.
The value
.Va YY
tells to which line the change would bring
.Ar file1
in line with
.Ar file2 .
.It Li XX,YY Ns Ic d Ns Li ZZ
Delete the range of lines
.Va XX
through
.Va YY
in
.Ar file1 .
.It Li XX Ns Ic c Ns Li YY
Change the line
.Va XX
in
.Ar file1
to the line
.Va YY
in
.Ar file2 .
.It Li XX,YY Ns Ic c Ns Li ZZ
Replace the range of specified lines with the line
.Va ZZ .
.It Li XX,YY Ns Ic c Ns Li ZZ,QQ
Replace the range
.Va XX , Ns Va YY
from
.Ar file1
with the range
.Va ZZ , Ns Va QQ
from
.Ar file2 .
.El
.Pp
These lines resemble
.Xr ed 1
subcommands to convert
.Ar file1
into
.Ar file2 .
The line numbers before the action letters pertain to
.Ar file1 ;
those after pertain to
.Ar file2 .
Thus, by exchanging
.Ic a
for
.Ic d
and reading the line in reverse order, one can also
determine how to convert
.Ar file2
into
.Ar file1 .
As in
.Xr ed 1 ,
identical
pairs (where num1 = num2) are abbreviated as a single
number.
.Sh ENVIRONMENT
.Bl -tag -width DIFFCOLORS
.It Ev DIFFCOLORS
The value of this variable is the form
.Ar add : Ns Ar rm ,
where
.Ar add
is the ASCII escape sequence for additions and
.Ar rm
is the ASCII escape sequence for deletions.
If this is unset,
.Nm
uses green for additions and red for removals.
.El
.Sh FILES
.Bl -tag -width /tmp/diff.XXXXXXXX -compact
.It Pa /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.
.El
.Sh EXIT STATUS
The
.Nm
utility exits with one of the following values:
.Pp
.Bl -tag -width Ds -offset indent -compact
.It 0
No differences were found.
.It 1
Differences were found.
.It >1
An error occurred.
.El
.Pp
The
.Fl -help
and
.Fl -version
options exit with a status of 0.
.Sh EXAMPLES
Compare
.Pa old_dir
and
.Pa new_dir
recursively generating an unified diff and treating files found only in one
of those directories as new files:
.Bd -literal -offset indent
$ diff -ruN /path/to/old_dir /path/to/new_dir
.Ed
.Pp
Same as above but excluding files matching the expressions
.Dq *.h
and
.Dq *.c :
.Bd -literal -offset indent
$ diff -ruN -x '*.h' -x '*.c' /path/to/old_dir /path/to/new_dir
.Ed
.Pp
Show a single line indicating if the files differ:
.Bd -literal -offset indent
$ diff -q /boot/loader.conf /boot/defaults/loader.conf
Files /boot/loader.conf and /boot/defaults/loader.conf differ
.Ed
.Pp
Assuming a file named
.Pa example.txt
with the following contents:
.Bd -literal -offset indent
FreeBSD is an operating system
Linux is a kernel
OpenBSD is an operating system
.Ed
.Pp
Compare stdin with
.Pa example.txt
excluding from the comparison those lines containing either
.Qq Linux
or
.Qq Open :
.Bd -literal -offset indent
$ echo "FreeBSD is an operating system" | diff -q -I 'Linux|Open' example.txt -
.Ed
.Sh SEE ALSO
.Xr cmp 1 ,
.Xr comm 1 ,
.Xr diff3 1 ,
.Xr ed 1 ,
.Xr patch 1 ,
.Xr pr 1 ,
.Xr sdiff 1
.Rs
.%A James W. Hunt
.%A M. Douglas McIlroy
.%T "An Algorithm for Differential File Comparison"
.%J Computing Science Technical Report
.%Q Bell Laboratories 41
.%D June 1976
.Re
.Sh STANDARDS
The
.Nm
utility is compliant with the
.St -p1003.1-2008
specification.
.Pp
The flags
.Op Fl AaDdIiLlNnPpqSsTtwXxy
are extensions to that specification.
.Sh HISTORY
A
.Nm
command appeared in
.At v6 .
The
.Nm
implementation used in
.Fx
was GNU diff until
.Fx 11.4 .
This was replaced in
.Fx 12.0
by a BSD-licensed implementation written by
.An Todd Miller .
Some GNUisms were lost in the process.
.Pp
libdiff was imported from the Game of Trees version control system and default
algorithm was changed to Myers for
.Fx 15 .