Editing Cmp (Unix)

{{Short description|Computer file comparison utility}}
{{lowercase title}}
{{Infobox software
| name                   = cmp
| logo                   = 
| author                 = [[Dennis Ritchie]]<br />([[AT&T Bell Laboratories]])
| developer              = Various [[open-source software|open-source]] and [[commercial software|commercial]] developers
| released               = {{Start date and age|1971|11|3}}
| latest release version = 
| latest release date    = 
| programming language   = Plan 9: [[C (programming language)|C]]
| operating system       = [[Unix]], [[Unix-like]], [[Plan 9 from Bell Labs|Plan 9]], [[Inferno (operating system)|Inferno]], [[OS-9]], [[IBM i]]
| genre                  = [[Command (computing)|Command]]
| license                = [[coreutils]]: [[GPLv3+]]<br />Plan 9: [[MIT License]]
| website                = 
}}
In [[computing]], '''<code>cmp</code>''' is a [[command-line interface|command-line]] utility on [[Unix]] and [[Unix-like]] [[operating system]]s that compares two [[Computer file|files]] of any type and writes the results to the [[standard output]]. By default, <code>cmp</code> is silent if the files are the same; if they differ, the [[byte]] and line number at which the first difference occurred is reported. The command is also available in the [[OS-9]] shell.<ref>{{cite book|author=Paul S. Dayan|year=1992|title=The OS-9 Guru - 1 : The Facts|publisher=Galactic Industrial Limited|isbn=0-9519228-0-7}}</ref>

==History==
{{code|cmp}} is part of the [[X/Open]] Portability Guide since issue 2 of 1987. It was inherited into the first version of POSIX.1 and the [[Single Unix Specification]].<ref>{{man|cu|printf|SUS}}</ref> It first appeared in [[Ancient Unix|Version 1 Unix]].<ref>{{man|1|cmp|FreeBSD}}</ref>
The version of <code>cmp</code> bundled in [[GNU]] [[coreutils]] was written by Torbjorn Granlund and David MacKenzie.<ref>{{Cite web|url=https://linux.die.net/man/1/cmp|title=cmp(1): compare two files byte by byte - Linux man page|website=linux.die.net}}</ref>
The command is available as a separate package for Microsoft Windows as part of the [[UnxUtils]] collection of [[Native (computing)|native]] [[Windows API|Win32]] [[porting|ports]] of common GNU Unix-like utilities.<ref>{{Cite web|url=http://unxutils.sourceforge.net/|title=Native Win32 ports of some GNU utilities|website=unxutils.sourceforge.net}}</ref> The {{Mono|cmp}} command has also been ported to the [[IBM i]] operating system.<ref>{{cite web |title=IBM System i Version 7.2 Programming Qshell |language=en |author=IBM |website=[[IBM]] |author-link=IBM |url=https://www.ibm.com/support/knowledgecenter/ssw_ibm_i_74/rzahz/rzahzpdf.pdf?view=kc |access-date=2020-09-05 }}</ref>

==Switches==
{{mono|cmp}} may be qualified by the use of [[Command-line argument|command-line switches]]. The switches supported by notable implementations of {{mono|cmp}} are:

{| class="wikitable" border="6"
! Name
! Description
! [[Unix]]
! [[Plan 9 from Bell Labs|Plan&nbsp;9]]
! [[Inferno (operating system)|Inferno]]
! [[FreeBSD]]
! [[Linux]]
! {{nowrap|[[IBM i]]}}
|-
| {{mono|-b,<br />--print-bytes}}
| Print the differing bytes. Display control bytes as a '{{mono|^}}' followed by a letter of the alphabet and precede bytes that have the high bit set with '{{mono|M-}}' (which stands for "[[Meta_key|meta]]").
| {{No}}
| {{No}}
| {{No}}
| {{No}}
| {{Yes}}
| {{No}}
|-
| {{mono|-h}}
| Do not follow symbolic links.
| {{No}}
| {{No}}
| {{No}}
| {{Yes}}
| {{No}}
| {{No}}
|-
| {{mono|1=-i SKIP,<br />--ignore-initial=SKIP}}
| Skip the first SKIP bytes of input.
| {{No}}
| {{No}}
| {{No}}
| {{No}}
| {{Yes}}
| {{No}}
|-
| {{mono|1=-i SKIP1:SKIP2,<br />--ignore-initial=SKIP1:SKIP2}}
| Skip the first SKIP1 bytes of FILE1 and the first SKIP2 bytes of FILE2.
| {{No}}
| {{No}}
| {{No}}
| {{No}}
| {{Yes}}
| {{No}}
|-
| {{mono|-l,<br />--verbose}}
| Output the (decimal) byte numbers and (octal) values of all differing bytes, instead of the default standard output.<br>
Also, output the EOF message if one file is shorter than the other.
| {{Yes}}
| {{Yes}}
| {{Yes}}
| {{Yes}}
| {{Yes}}
| {{Yes}}
|-
| {{mono|-L}}
| Print the line number of the first differing byte.
| {{Yes}}
| {{Yes}}
| {{Yes}}
| {{No}}
| {{No}}
| {{No}}
|-
| {{mono|1=-n LIMIT,<br />--bytes=LIMIT}}
| Compare at most LIMIT bytes.
| {{No}}
| {{No}}
| {{No}}
| {{No}}
| {{Yes}}
| {{No}}
|-
| {{mono|-s,<br />--quiet,<br />--silent}}
| Output nothing; yield exit status only.
| {{Yes}}
| {{Yes}}
| {{Yes}}
| {{Yes}}
| {{Yes}}
| {{Yes}}
|-
| {{mono|-t}}
| Text mode where the files are opened in text mode and translated to the [[CCSID]] of the job before comparing byte for byte.
| {{No}}
| {{No}}
| {{No}}
| {{No}}
| {{No}}
| {{Yes}}
|-
| {{mono|-v,<br />--version}}
| Output version info.
| {{No}}
| {{No}}
| {{No}}
| {{No}}
| {{Yes}}
| {{No}}
|-
| {{mono|-x}}
| Like -l but prints in hexadecimal and using zero as index for the first byte in the files.
| {{No}}
| {{No}}
| {{No}}
| {{Yes}}
| {{No}}
| {{No}}
|-
| {{mono|-z}}
| For regular files compare file sizes first, and fail the comparison if they are not equal.
| {{No}}
| {{No}}
| {{No}}
| {{Yes}}
| {{No}}
| {{No}}
|-
| {{mono|--help}}
| Outputs a help file.
| {{No}}
| {{No}}
| {{No}}
| {{No}}
| {{Yes}}
| {{No}}
|}

Operands that are byte counts are normally decimal, but may be preceded by '{{mono|0}}' for octal and '{{mono|0x}}' for hexadecimal.

A byte count can be followed by a suffix to specify a multiple of that count; in this case an omitted integer is understood to be 1. A bare size letter, or one followed by '{{mono|iB}}', specifies a multiple using powers of 1024. A size letter followed by '{{mono|B}}' specifies powers of 1000 instead. For example, '{{mono|-n 4M}}' and '{{mono|-n 4MiB}}' are equivalent to '{{mono|-n 4194304}}', whereas '{{mono|-n 4MB}}' is equivalent to '{{mono|-n 4000000}}'.  This notation is upward compatible with the SI prefixes<ref>{{cite web| url = http://www.bipm.fr/enus/3_SI/si-prefixes.html |title = Welcome - BIPM}}</ref> for decimal multiples and with the IEC 60027-2 prefixes for binary multiples.<ref>{{cite web|url=https://physics.nist.gov/cuu/Units/binary.html|title=Definitions of the SI units: The binary prefixes|website=physics.nist.gov|access-date=21 April 2018}}</ref>

==Example== 
[[File:Cmp-example-command-gimp.gif|thumb|520px|none|Example usage of {{code|cmp}} to find different bytes between 2 txt files]]

==Return values==
* 0 – files are identical
* 1 – files differ
* 2 – inaccessible or missing argument

==See also==
* [[Comparison of file comparison tools]]
* [[List of Unix commands]]

==References==
{{Reflist}}

==External links==
{{Wikibooks|Guide to Unix|Commands}}
* {{man|cu|cmp|SUS|compare two files}}
* [https://www.gnu.org/software/diffutils/manual/html_node/Invoking-cmp.html ''Comparing and Merging Files'': Invoking cmp] The section of the manual of GNU cmp in the [[diffutils]] [[free manual]].

{{Unix commands}}
{{Plan 9 commands}}

[[Category:Free file comparison tools]]
[[Category:Standard Unix programs]]
[[Category:Unix SUS2008 utilities]]
[[Category:Plan 9 commands]]
[[Category:Inferno (operating system) commands]]
[[Category:IBM i Qshell commands]]