Invoking @command{cmp}

The @command{cmp} command compares two files, and if they differ, tells the first byte and line number where they differ. Bytes and lines are numbered starting with 1. The arguments of @command{cmp} are as follows:

cmp options... from-file [to-file [from-skip [to-skip]]]

The file name `-' is always the standard input. @command{cmp} also uses the standard input if one file name is omitted. The from-skip and to-skip operands specify how many bytes to ignore at the start of each file; they are equivalent to the @option{--ignore-initial=from-skip:to-skip} option.

An exit status of 0 means no differences were found, 1 means some differences were found, and 2 means trouble.

Options to @command{cmp}

Below is a summary of all of the options that GNU @command{cmp} accepts. Most options have two equivalent names, one of which is a single letter preceded by `-', and the other of which is a long name preceded by `--'. Multiple single letter options (unless they take an argument) can be combined into a single command line word: @option{-bl} is equivalent to @option{-b -l}.

@option{-b}

@option{--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").

@option{--help}

Output a summary of usage and then exit.

@option{-i skip}

@option{--ignore-initial=skip}

Ignore any differences in the first skip bytes of the input files. Treat files with fewer than skip bytes as if they are empty. If skip is of the form @option{from-skip:to-skip}, skip the first from-skip bytes of the first input file and the first to-skip bytes of the second.

@option{-l}

@option{--verbose}

Print the (decimal) byte numbers and (octal) values of all differing bytes.

@option{-n count}

@option{--bytes=count}

Compare at most count input bytes.

@option{-s}

@option{--quiet}

@option{--silent}

Do not print anything; only return an exit status indicating whether the files differ.

@option{-v}

@option{--version}

Output version information and then exit.

In the above table, 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, @option{-n 4M} and @option{-n 4MiB} are equivalent to @option{-n 4194304}, whereas @option{-n 4MB} is equivalent to @option{-n 4000000}. This notation is upward compatible with the SI prefixes for decimal multiples and with the IEC 60027-2 prefixes for binary multiples.

The following suffixes are defined. Large sizes like 1Y may be rejected by your computer due to limitations of its arithmetic.

`kB'

kilobyte: 10^3 = 1000.

`k'

`K'

`KiB'

kibibyte: 2^10 = 1024. `K' is special: the SI prefix is `k' and the IEC 60027-2 prefix is `Ki', but tradition and POSIX use `k' to mean `KiB'.

`MB'

megabyte: 10^6 = 1,000,000.

`M'

`MiB'

mebibyte: 2^20 = 1,048,576.

`GB'

gigabyte: 10^9 = 1,000,000,000.

`G'

`GiB'

gibibyte: 2^30 = 1,073,741,824.

`TB'

terabyte: 10^12 = 1,000,000,000,000.

`T'

`TiB'

tebibyte: 2^40 = 1,099,511,627,776.

`PB'

petabyte: 10^15 = 1,000,000,000,000,000.

`P'

`PiB'

pebibyte: 2^50 = 1,125,899,906,842,624.

`EB'

exabyte: 10^18 = 1,000,000,000,000,000,000.

`E'

`EiB'

exbibyte: 2^60 = 1,152,921,504,606,846,976.

`ZB'

zettabyte: 10^21 = 1,000,000,000,000,000,000,000

`Z'

`ZiB'

2^70 = 1,180,591,620,717,411,303,424. (`Zi' is a GNU extension to IEC 60027-2.)

`YB'

yottabyte: 10^24 = 1,000,000,000,000,000,000,000,000.

`Y'

`YiB'

2^80 = 1,208,925,819,614,629,174,706,176. (`Yi' is a GNU extension to IEC 60027-2.)

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