Originální popis anglicky:
cmp - compare two files
Návod, kniha: POSIX Programmer's Manual
cmp [ -l | -s ] file1 file2
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.
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.
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.
The standard input shall be used only if the
file1 or
file2
operand refers to standard input. See the INPUT FILES section.
The input files can be any file type.
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
- Determine the location of message catalogs for the
processing of LC_MESSAGES .
Default.
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.
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.
None.
None.
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.
Default.
The following sections are informative.
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 <newline>, without any implication that the file is organized into
lines.
None.
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:
to be an error. They also treat:
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>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.
None.
comm ,
diff
Portions of this text are reprinted and reproduced in electronic form from IEEE
Std 1003.1, 2003 Edition, Standard for Information Technology -- Portable
Operating System Interface (POSIX), The Open Group Base Specifications Issue
6, Copyright (C) 2001-2003 by the Institute of Electrical and Electronics
Engineers, Inc and The Open Group. In the event of any discrepancy between
this version and the original IEEE and The Open Group Standard, the original
IEEE and The Open Group Standard is the referee document. The original
Standard can be obtained online at http://www.opengroup.org/unix/online.html
.
