ECHO(1P) POSIX Programmer's Manual ECHO(1P)
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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
POSIX.1-2008, 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 oper-
and 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 follow-
ing 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.
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 vari-
ables that are unset or null. (See the Base Definitions vol-
ume of POSIX.1-2008, 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> charac-
ters 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.
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 POSIX.1-2008 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> characters or that could possi-
bly 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
The Base Definitions volume of POSIX.1-2008, Chapter 8, Environment
Variables, Section 12.2, Utility Syntax Guidelines
COPYRIGHT
Portions of this text are reprinted and reproduced in electronic form
from IEEE Std 1003.1, 2013 Edition, Standard for Information Technology
-- Portable Operating System Interface (POSIX), The Open Group Base
Specifications Issue 7, Copyright (C) 2013 by the Institute of Electri-
cal and Electronics Engineers, Inc and The Open Group. (This is
POSIX.1-2008 with the 2013 Technical Corrigendum 1 applied.) 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.unix.org/online.html .
Any typographical or formatting errors that appear in this page are
most likely to have been introduced during the conversion of the source
files to man page format. To report such errors, see https://www.ker-
nel.org/doc/man-pages/reporting_bugs.html .
IEEE/The Open Group 2013 ECHO(1P)
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