сравнить два файла (compare two files)
Пролог (Prolog)
This manual page is part of the POSIX Programmer's Manual. The
Linux implementation of this interface may differ (consult the
corresponding Linux manual page for details of Linux behavior),
or the interface may not be implemented on Linux.
Имя (Name)
cmp — compare two files
Синопсис (Synopsis)
cmp [-l|-s] file1 file2
Описание (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.
Параметры (Options)
The cmp utility shall conform to the Base Definitions volume of
POSIX.1‐2017, 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 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.
Операнды (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.
Стандартный ввод (Stdin)
The standard input shall be used only if the file1 or file2
operand refers to standard input. See the INPUT FILES section.
Входные файлы (Input files)
The input files can be any file type.
Переменные окружения (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 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.
Асинхронные события (Asynchronous events)
Default.
Стандартный вывод (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.
Стандартный вывод сообщений (Stderr)
The standard error shall be used only for diagnostic messages. If
the -l option is used and file1 and file2 differ in length, or if
the -s option is not used and file1 and file2 are identical for
the entire length of the shorter file, in the POSIX locale the
following diagnostic message shall be written:
"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.
Выходные файлы (Output files)
None.
Расширенное описание (Extended description)
None.
Статус выхода (Exit)
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.
Последствия ошибок (Consequences of errors)
Default.
The following sections are informative.
Использование в приложениях (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
POSIX.1‐2017. Since this volume of POSIX.1‐2017 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.
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
}
Примеры (Examples)
None.
Обоснование (Rationale)
The global language in Section 1.4, 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 <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.
Будущие направления (Future directions)
Future versions of this standard may require that diagnostic
messages are written to standard error when the -s option is
specified.
Смотри также (See also)
comm(1p), diff(1p)
The Base Definitions volume of POSIX.1‐2017, Chapter 8,
Environment Variables, Section 12.2, Utility Syntax Guidelines
