Cmp (Unix)

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

cmp is a shell command that compares two files of any type and reports differences. By default, it outputs nothing if the files match. If they differ, it reports the byte and line number of the first difference. The exit code can be used programmatically since it is 0 if the files match, 1 if the files differ or 2 if comparison fails (i.e. inaccessible or missing argument).

Contents

The command is available on Unix-like systems, OS-9, IBM i and Windows (via UnxUtils). [1] [2] [3] The command first appeared in Version 1 Unix. [4] It 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. [5] The implementation in GNU coreutils was written by Torbjorn Granlund and David MacKenzie. [6]

Use

Command line options include:

OptionDescription 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")NoNoNoNoYesNo
-hDo not follow symbolic linksNoNoNoYesNoNo
-i SKIP,
--ignore-initial=SKIP
Skip the first SKIP bytes of inputNoNoNoNoYesNo
-i SKIP1:SKIP2,
--ignore-
initial=
SKIP1:SKIP2
Skip the first SKIP1 bytes of FILE1 and the first SKIP2 bytes of FILE2NoNoNoNoYesNo
-l,
--verbose
Print the (decimal) byte numbers and (octal) values of all differing bytes, instead of the default info; also, print the EOF message if one file is shorter than the otherYesYesYesYesYesYes
-LPrint the line number of the first differing byteYesYesYesNoNoNo
-n LIMIT,
--bytes=LIMIT
Compare at most LIMIT bytesNoNoNoNoYesNo
-s,
--quiet,
--silent
Print nothing; yield exit status onlyYesYesYesYesYesYes
-tText mode where the files are opened in text mode and translated to the CCSID of the job before comparing byte for byteNoNoNoNoNoYes
-v,
--version
Print version infoNoNoNoNoYesNo
-xLike -l but prints in hexadecimal and using zero as index for the first byte in the filesNoNoNoYesNoNo
-zFor regular files, compare file sizes first, and fail if they are not equalNoNoNoYesNoNo
--helpPrint command-line help infoNoNoNoNoYesNo

Operands that are byte counts are decimal by default, 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

Example use to report different bytes between text files Cmp-example-command-gimp.gif
Example use to report different bytes between text files

See also

References

  1. Paul S. Dayan (1992). The OS-9 Guru - 1 : The Facts. Galactic Industrial Limited. ISBN   0-9519228-0-7.
  2. IBM. "IBM System i Version 7.2 Programming Qshell" (PDF). IBM . Retrieved 2020-09-05.
  3. "Native Win32 ports of some GNU utilities". unxutils.sourceforge.net.
  4. cmp(1)    FreeBSD General Commands Manual
  5. printf   Shell and Utilities Reference, The Single UNIX Specification , Version 5 from The Open Group
  6. "cmp(1): compare two files byte by byte - Linux man page". linux.die.net.
  7. "Welcome - BIPM".
  8. "Definitions of the SI units: The binary prefixes". physics.nist.gov. Retrieved 21 April 2018.