cmp (Unix)

In computing, cmp is a command-line utility for computer systems that use Unix or a Unix-like operating system. It 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]

cmp
Original author(s)Dennis Ritchie
Developer(s)AT&T Bell Laboratories
Initial releaseNovember 3, 1971 (1971-11-03)
Operating systemUnix, Unix-like, Plan 9, Inferno, OS-9
TypeCommand
Licensecoreutils: GPLv3+

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]

Switches

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

-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").
-i SKIP, --ignore-initial=SKIP
Skip the first SKIP bytes of input.
-i SKIP1:SKIP2, --ignore-initial=SKIP1:SKIP2 : Skip the first SKIP1 bytes of FILE1 and the first SKIP2 bytes of FILE2.
-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.
-n LIMIT, --bytes=LIMIT
Compare at most LIMIT bytes.
-s, --quiet, --silent
Output nothing; yield exit status only.
-v, --version
Output version info.
--help
Outputs a help file.

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[5] for decimal multiples and with the IEC 60027-2 prefixes for binary multiples.[6]

Return values
  • 0 – files are identical
  • 1 – files differ
  • 2 – inaccessible or missing argument
gollark: I'll go check the IR logs.
gollark: Is it not? Might be invalid then.
gollark: Not all of them are copy-protected, and not all of them allow all permissions, and whatnot.
gollark: https://pastebin.com/viz0spjb
gollark: I'll pull up the full list.

See also

References
  1. Paul S. Dayan (1992). The OS-9 Guru - 1 : The Facts. Galactic Industrial Limited. ISBN 0-9519228-0-7.
  2. printf – Commands & Utilities Reference, The Single UNIX Specification, Issue 7 from The Open Group
  3. cmp(1) – FreeBSD General Commands Manual
  4. https://linux.die.net/man/1/cmp
  5. http://www.bipm.fr/enus/3_SI/si-prefixes.html
  6. "Definitions of the SI units: The binary prefixes". physics.nist.gov. Retrieved 21 April 2018.
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