cmp(1p) - phpMan

CMP(P) CMP(P)

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 â€â€™-â€â€™ , the standard
input shall be used.

file2 A pathname of the second file to be compared. If file2 is â€â€™-â€â€™ , 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 stan-
dard 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 interna-
tionalization 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 char-
acters 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
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
<blank> and contains no <newline>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, compar-
isons 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
<newline>, without any implication that the file is organized into lines.

EXAMPLES
None.

RATIONALE
The global language in Utility Description Defaults indicates that using two mutu-
ally-exclusive options together produces unspecified results. Some System V imple-
mentations 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, imple-
mentations are encouraged to use the word byte or its equivalent in another lan-
guage. Users should not interpret this difference to indicate that the functional-
ity 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>s is to
make parsing for the filename easier. It is recognized that some filenames contain-
ing 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.