cmp (Unix)

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.

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. It first appeared in Version 1 Unix. The version of cmp bundled in GNU coreutils was written by Torbjorn Granlund and David MacKenzie. 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. The

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

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 for decimal multiples and with the IEC 60027-2 prefixes for binary multiples.

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

• Comparison of file comparison tools
• List of Unix commands

• 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.