cmp (original) (raw)

The Open Group Base Specifications Issue 6
IEEE Std 1003.1, 2004 Edition
Copyright © 2001-2004 The IEEE and The Open Group, All Rights reserved.

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NAME

cmp - compare two files

SYNOPSIS

cmp **[** -l | -s **]** _file1 file2_

DESCRIPTION

The cmp utility shall compare two files. The cmp utility shall write no output if the files are the same. Under default options, if they differ, it shall write to standard output the byte and line number at which the first difference occurred. Bytes and lines shall be numbered beginning with 1.

OPTIONS

The cmp utility shall conform to the Base Definitions volume of IEEE Std 1003.1-2001, Section 12.2, Utility Syntax Guidelines.

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 for differing files; return exit status only.

OPERANDS

The following operands shall be supported:

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

The standard input shall be used only if the file1 or file2 operand refers to standard input. See the INPUT FILES section.

INPUT FILES

The input files can be any file type.

ENVIRONMENT VARIABLES

The following environment variables shall affect the execution of cmp:

LANG

Provide a default value for the internationalization variables that are unset or null. (See the Base Definitions volume of IEEE Std 1003.1-2001, 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

[XSI] Determine the location of message catalogs for the processing of LC_MESSAGES .

ASYNCHRONOUS EVENTS

Default.

STDOUT

In the POSIX locale, results of the comparison shall be written to standard output. When no options are used, the format shall be:

"%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

The standard error shall be used only for diagnostic messages. If file1 and file2 are identical for the entire length of the shorter file, in the POSIX locale the following diagnostic message shall be written, unless the -s option is specified:

"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 and contains no s. Some implementations report on the number of lines in this case.

OUTPUT FILES

None.

EXTENDED DESCRIPTION

None.

EXIT STATUS

The following exit values shall be returned:

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

Default.

The following sections are informative.

APPLICATION USAGE

Although input files to cmp can be any type, the results might not be what would be expected on character special device files or on file types not described by the System Interfaces volume of IEEE Std 1003.1-2001. Since this volume of IEEE Std 1003.1-2001 does not specify the block size used when doing input, comparisons of character special files need not compare all of the data in those files.

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

EXAMPLES

None.

RATIONALE

The global language in Utility Description Defaults indicates that using two mutually-exclusive options together produces unspecified results. Some System V implementations consider the option usage:

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 and no s 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

None.

SEE ALSO

comm, diff

CHANGE HISTORY

First released in Issue 2.

End of informative text.

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POSIX ® is a registered Trademark of The IEEE.
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