Cmp (Unix)

cmp
Original author(s)	Dennis Ritchie; (AT&T Bell Laboratories)
Developer(s)	Various open-source and commercial developers
Initial release	November 3, 1971; 53 years ago
Written in	Plan 9: C
Operating system	Unix, Unix-like, Plan 9, Inferno, OS-9, IBM i
Type	Command
License	coreutils: GPLv3+; Plan 9: MIT License

In computing, cmp is a command-line utility on Unix and Unix-like operating systems that compares two files of any type and writes the results to the standard output. By default, cmp 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.^[1]

History

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.^[2] It first appeared in Version 1 Unix.^[3] The version of cmp bundled in GNU coreutils was written by Torbjorn Granlund and David MacKenzie.^[4] The command is available as a separate package for Microsoft Windows as part of the UnxUtils collection of native Win32 ports of common GNU Unix-like utilities.^[5] The cmp command has also been ported to the IBM i operating system.^[6]

Switches

cmp may be qualified by the use of command-line switches. The switches supported by notable implementations of cmp are:

Name	Description	Unix	Plan 9	Inferno	FreeBSD	Linux	IBM i
`-b, --print-bytes`	Print the differing bytes. Display control bytes as a '`^`' followed by a letter of the alphabet and precede bytes that have the high bit set with '`M-`' (which stands for "meta").	No	No	No	No	Yes	No
`-h`	Do not follow symbolic links.	No	No	No	Yes	No	No
`-i SKIP, --ignore-initial=SKIP`	Skip the first SKIP bytes of input.	No	No	No	No	Yes	No
`-i SKIP1:SKIP2, --ignore-initial=SKIP1:SKIP2`	Skip the first SKIP1 bytes of FILE1 and the first SKIP2 bytes of FILE2.	No	No	No	No	Yes	No
`-l, --verbose`	Output the (decimal) byte numbers and (octal) values of all differing bytes, instead of the default standard output. Also, output the EOF message if one file is shorter than the other.	Yes	Yes	Yes	Yes	Yes	Yes
`-L`	Print the line number of the first differing byte.	Yes	Yes	Yes	No	No	No
`-n LIMIT, --bytes=LIMIT`	Compare at most LIMIT bytes.	No	No	No	No	Yes	No
`-s, --quiet, --silent`	Output nothing; yield exit status only.	Yes	Yes	Yes	Yes	Yes	Yes
`-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
`-v, --version`	Output version info.	No	No	No	No	Yes	No
`-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
`-z`	For regular files compare file sizes first, and fail the comparison if they are not equal.	No	No	No	Yes	No	No
`--help`	Outputs a help file.	No	No	No	No	Yes	No

Operands that are byte counts are normally decimal, but may be preceded by '0' for octal and '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 'iB', specifies a multiple using powers of 1024. A size letter followed by 'B' specifies powers of 1000 instead. For example, '-n 4M' and '-n 4MiB' are equivalent to '-n 4194304', whereas '-n 4MB' is equivalent to '-n 4000000'. This notation is upward compatible with the SI prefixes^[7] for decimal multiples and with the IEC 60027-2 prefixes for binary multiples.^[8]

Example

Return values

0 – files are identical
1 – files differ
2 – inaccessible or missing argument

References

^ Paul S. Dayan (1992). The OS-9 Guru - 1 : The Facts. Galactic Industrial Limited. ISBN 0-9519228-0-7.
^ printf – Shell and Utilities Reference, The Single UNIX Specification, Version 4 from The Open Group
^ cmp(1) – FreeBSD General Commands Manual
^ "cmp(1): compare two files byte by byte - Linux man page". linux.die.net.
^ "Native Win32 ports of some GNU utilities". unxutils.sourceforge.net.
^ IBM. "IBM System i Version 7.2 Programming Qshell" (PDF). IBM. Retrieved 2020-09-05.
^ "Welcome - BIPM".
^ "Definitions of the SI units: The binary prefixes". physics.nist.gov. Retrieved 21 April 2018.

External links

cmp: compare two files – Shell and Utilities Reference, The Single UNIX Specification, Version 4 from The Open Group
Comparing and Merging Files: Invoking cmp The section of the manual of GNU cmp in the diffutils free manual.

≥

[1] Paul S. Dayan (1992). The OS-9 Guru - 1 : The Facts. Galactic Industrial Limited. ISBN 0-9519228-0-7.

[2] printf – Shell and Utilities Reference, The Single UNIX Specification, Version 4 from The Open Group

[3] cmp(1) – FreeBSD General Commands Manual

[4] "cmp(1): compare two files byte by byte - Linux man page". linux.die.net.

[5] "Native Win32 ports of some GNU utilities". unxutils.sourceforge.net.

[6] IBM. "IBM System i Version 7.2 Programming Qshell" (PDF). IBM. Retrieved 2020-09-05.

[7] "Welcome - BIPM".

[8] "Definitions of the SI units: The binary prefixes". physics.nist.gov. Retrieved 21 April 2018.

[1]

[2]

[3]

[4]

[5]

[6]

[7]

[8]

v t e Unix command-line interface programs and shell builtins
File system	cat chattr chmod chown chgrp cksum cmp cp dd du df file fuser ln ls mkdir mv pax pwd rm rmdir split tee touch type umask
Processes	at bg crontab fg kill nice ps time
User environment	env exit logname mesg talk tput uname who write
Text processing	awk basename comm csplit cut diff dirname ed ex fold head iconv join m4 more nl paste patch printf read sed sort strings tail tr troff uniq vi wc xargs
Shell builtins	alias cd echo test unset wait
Searching	find grep
Documentation	man
Software development	ar ctags lex make nm strip yacc
Miscellaneous	bc cal expr lp od sleep true and false
Categories Standard Unix programs Unix SUS2008 utilities List

v t e Plan 9 command-line interface programs and shell builtins
File system	chmod chgrp cmp cp dd du file gzip ls mkdir pwd rm split tee touch
Processes	kill ps
User environment	passwd who
Text processing	awk basename comm diff ed eqn join sed sort spell strings tail tr troff uniq wc
Shell builtins	echo test
Networking	ip/ipconfig ip/ping netstat
Searching	grep
Software development	ar hoc lex nm strip yacc
Miscellaneous	bc cal fortune sleep
Category

Original author(s)	Dennis Ritchie (AT&T Bell Laboratories)
Developer(s)	Various open-source and commercial developers
Initial release	November 3, 1971; 53 years ago (1971-11-03)
Written in	Plan 9: C
Operating system	Unix, Unix-like, Plan 9, Inferno, OS-9, IBM i
Type	Command
License	coreutils: GPLv3+ Plan 9: MIT License