ECHO(1P) POSIX Programmer's Manual ECHO(1P)
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.
NAME
echo - write arguments to standard output
SYNOPSIS
echo [string ...]
DESCRIPTION
The echo utility writes its arguments to standard output, followed by a
<newline>. If there are no arguments, only the <newline> is written.
OPTIONS
The echo utility shall not recognize the "--" argument in the manner
specified by Guideline 10 of the Base Definitions volume of
IEEE Std 1003.1-2001, Section 12.2, Utility Syntax Guidelines; "--"
shall be recognized as a string operand.
Implementations shall not support any options.
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 argu-
ments:
\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 argu-
ments 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.
STDIN
Not used.
INPUT FILES
None.
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
IEEE Std 1003.1-2001, Section 8.2, Internationalization Vari-
ables 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 .
ASYNCHRONOUS EVENTS
Default.
STDOUT
The echo utility arguments shall be separated by single <space>s and a
<newline> shall follow the last argument. Output transformations shall
occur based on the escape sequences in the input. See the OPERANDS sec-
tion.
STDERR
The standard error shall be used only for diagnostic messages.
OUTPUT FILES
None.
EXTENDED DESCRIPTION
None.
EXIT STATUS
The following exit values shall be returned:
0 Successful completion.
>0 An error occurred.
CONSEQUENCES OF ERRORS
Default.
The following sections are informative.
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 tradi-
tional 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 implementa-
tions in this volume of IEEE Std 1003.1-2001 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.
EXAMPLES
None.
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>s 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.
FUTURE DIRECTIONS
None.
SEE ALSO
printf
COPYRIGHT
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 .
IEEE/The Open Group 2003 ECHO(1P)
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