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12 Invoking cmp

The cmp command compares two files, and if they differ, tells the first byte and line number where they differ or reports that one file is a prefix of the other. Bytes and lines are numbered starting with 1. The arguments of cmp are as follows:

cmp optionsfrom-file [to-file [from-skip [to-skip]]]

The file name - is always the standard input. 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 --ignore-initial=from-skip:to-skip option.

By default, cmp outputs nothing if the two files have the same contents. If the two files have bytes that differ, cmp reports the location of the first difference to standard output:

from-file to-file differ: char byte-number, line line-number

If one file is a prefix of the other, cmp reports the shorter file’s name to standard error, followed by a blank and extra information about the shorter file:

cmp: EOF on shorter-file extra-info

The message formats can differ outside the POSIX locale. POSIX allows but does not require the EOF diagnostic’s file name to be followed by a blank and additional information.

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

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