CMP

PROLOG

NAME

SYNOPSIS

cmp [-l|-s] file1 file2

DESCRIPTION

OPTIONS

The following options shall be supported:

-l

(Lowercase ell.) Write the byte number (decimal) and the differing bytes (octal) for each difference.

-s

Write nothing to standard output or standard error when files differ; indicate differing files through exit status only. It is unspecified whether a diagnostic message is written to standard error when an error is encountered; if a message is not written, the error is indicated through exit status only.

OPERANDS

file1

A pathname of the first file to be compared. If file1 is '-', the standard input shall be used.

file2

A pathname of the second file to be compared. If file2 is '-', the standard input shall be used.

If both file1 and file2 refer to standard input or refer to the same FIFO special, block special, or character special file, the results are undefined.  

STDIN

INPUT FILES

ENVIRONMENT VARIABLES

LANG

Provide a default value for the internationalization variables that are unset or null. (See the Base Definitions volume of POSIX.1-2017, Section 8.2, Internationalization Variables for the precedence of internationalization variables used to determine the values of locale categories.)

LC_ALL

If set to a non-empty string value, override the values of all the other internationalization variables.

LC_CTYPE

Determine the locale for the interpretation of sequences of bytes of text data as characters (for example, single-byte as opposed to multi-byte characters in arguments).

LC_MESSAGES

Determine the locale that should be used to affect the format and contents of diagnostic messages written to standard error and informative messages written to standard output.

NLSPATH

Determine the location of message catalogs for the processing of LC_MESSAGES.

ASYNCHRONOUS EVENTS

STDOUT

"%s %s differ: char %d, line %d\n", file1, file2,
    <byte number>, <line number>

When the -l option is used, the format shall be:

"%d %o %o\n", <byte number>, <differing byte>,
    <differing byte>

for each byte that differs. The first <differing byte> number is from file1 while the second is from file2. In both cases, <byte number> shall be relative to the beginning of the file, beginning with 1.

No output shall be written to standard output when the -s option is used.  

STDERR

"cmp: EOF on %s%s\n", <name of shorter file>, <additional info>

The <additional info> field shall either be null or a string that starts with a <blank> and contains no <newline> characters. Some implementations report on the number of lines in this case.

If the -s option is used and an error occurs, it is unspecified whether a diagnostic message is written to standard error.  

OUTPUT FILES

EXTENDED DESCRIPTION

EXIT STATUS

 0

The files are identical.

 1

The files are different; this includes the case where one file is identical to the first part of the other.

>1

An error occurred.

CONSEQUENCES OF ERRORS

The following sections are informative.  

APPLICATION USAGE

For files which are not text files, line numbers simply reflect the presence of a <newline>, without any implication that the file is organized into lines.

Since the behavior of -s differs between implementations as to whether error messages are written, the only way to ensure consistent behavior of cmp when -s is used is to redirect standard error to /dev/null.

If error messages are wanted, instead of using -s standard output should be redirected to /dev/null, and anything written to standard error should be discarded if the exit status is 1. For example:

silent_cmp() {
    # compare files with no output except error messages
    message=$(cmp "$@" 2>&1 >/dev/null)
    status=$?
    case $status in
    (0|1) ;;
    (*) printf '%s\n' "$message" ;;
    esac
    return $status
}

EXAMPLES

RATIONALE

cmp -l -s ...

to be an error. They also treat:

cmp -s -l ...

as if no options were specified. Both of these behaviors are considered bugs, but are allowed.

The word char in the standard output format comes from historical usage, even though it is actually a byte number. When cmp is supported in other locales, implementations are encouraged to use the word byte or its equivalent in another language. Users should not interpret this difference to indicate that the functionality of the utility changed between locales.

Some implementations report on the number of lines in the identical-but-shorter file case. This is allowed by the inclusion of the <additional info> fields in the output format. The restriction on having a leading <blank> and no <newline> characters is to make parsing for the filename easier. It is recognized that some filenames containing white-space characters make parsing difficult anyway, but the restriction does aid programs used on systems where the names are predominantly well behaved.  

FUTURE DIRECTIONS

SEE ALSO

The Base Definitions volume of POSIX.1-2017, Chapter 8, Environment Variables, Section 12.2, Utility Syntax Guidelines  

COPYRIGHT

Any typographical or formatting errors that appear in this page are most likely to have been introduced during the conversion of the source files to man page format. To report such errors, see https://www.kernel.org/doc/man-pages/reporting_bugs.html .

Index

PROLOG

NAME

SYNOPSIS

DESCRIPTION

OPTIONS

OPERANDS

STDIN

INPUT FILES

ENVIRONMENT VARIABLES

ASYNCHRONOUS EVENTS

STDOUT

STDERR

OUTPUT FILES

EXTENDED DESCRIPTION

EXIT STATUS

CONSEQUENCES OF ERRORS

APPLICATION USAGE

EXAMPLES

RATIONALE

FUTURE DIRECTIONS

SEE ALSO

COPYRIGHT