записывать аргументы в стандартный вывод (write arguments to standard output)
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)
echo — write arguments to standard output
Синопсис (Synopsis)
echo [string...]
Описание (Description)
The echo utility writes its arguments to standard output,
followed by a <newline>. If there are no arguments, only the
<newline> is written.
Параметры (Options)
The echo utility shall not recognize the "--" argument in the
manner specified by Guideline 10 of the Base Definitions volume
of POSIX.1‐2017, Section 12.2, Utility Syntax Guidelines; "--"
shall be recognized as a string operand.
Implementations shall not support any options.
Операнды (Operands)
The following operands shall be supported:
string A string to be written to standard output. If the first
operand is -n, or if any of the operands contain a
<backslash> character, the results are implementation-
defined.
On XSI-conformant systems, if the first operand is -n,
it shall be treated as a string, not an option. The
following character sequences shall be recognized on
XSI-conformant systems within any of the arguments:
\a Write an <alert>.
\b Write a <backspace>.
\c Suppress the <newline> that otherwise follows
the final argument in the output. All
characters following the '\c' in the arguments
shall be ignored.
\f Write a <form-feed>.
\n Write a <newline>.
\r Write a <carriage-return>.
\t Write a <tab>.
\v Write a <vertical-tab>.
\\ Write a <backslash> character.
\0num Write an 8-bit value that is the zero, one,
two, or three-digit octal number num.
Стандартный ввод (Stdin)
Not used.
Входные файлы (Input files)
None.
Переменные окружения (Environment variables)
The following environment variables shall affect the execution of
echo:
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.
NLSPATH Determine the location of message catalogs for the
processing of LC_MESSAGES.
Асинхронные события (Asynchronous events)
Default.
Стандартный вывод (Stdout)
The echo utility arguments shall be separated by single <space>
characters and a <newline> character shall follow the last
argument. Output transformations shall occur based on the escape
sequences in the input. See the OPERANDS section.
Стандартный вывод сообщений (Stderr)
The standard error shall be used only for diagnostic messages.
Выходные файлы (Output files)
None.
Расширенное описание (Extended description)
None.
Статус выхода (Exit)
The following exit values shall be returned:
0 Successful completion.
>0 An error occurred.
Последствия ошибок (Consequences of errors)
Default.
The following sections are informative.
Использование в приложениях (Application usage)
It is not possible to use echo portably across all POSIX systems
unless both -n (as the first argument) and escape sequences are
omitted.
The printf utility can be used portably to emulate any of the
traditional behaviors of the echo utility as follows (assuming
that IFS has its standard value or is unset):
* The historic System V echo and the requirements on XSI
implementations in this volume of POSIX.1‐2017 are equivalent
to:
printf "%b\n$*"
* The BSD echo is equivalent to:
if [ "X$1" = "X-n" ]
then
shift
printf "%s$*"
else
printf "%s\n$*"
fi
New applications are encouraged to use printf instead of echo.
Примеры (Examples)
None.
Обоснование (Rationale)
The echo utility has not been made obsolescent because of its
extremely widespread use in historical applications. Conforming
applications that wish to do prompting without <newline>
characters or that could possibly be expecting to echo a -n,
should use the printf utility derived from the Ninth Edition
system.
As specified, echo writes its arguments in the simplest of ways.
The two different historical versions of echo vary in fatally
incompatible ways.
The BSD echo checks the first argument for the string -n which
causes it to suppress the <newline> that would otherwise follow
the final argument in the output.
The System V echo does not support any options, but allows escape
sequences within its operands, as described for XSI
implementations in the OPERANDS section.
The echo utility does not support Utility Syntax Guideline 10
because historical applications depend on echo to echo all of its
arguments, except for the -n option in the BSD version.
Будущие направления (Future directions)
None.
Смотри также (See also)
printf(1p)
The Base Definitions volume of POSIX.1‐2017, Chapter 8,
Environment Variables, Section 12.2, Utility Syntax Guidelines
