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 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.
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 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
.
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 section. <img
src="../images/opt-end.gif" alt="[Option End]" border="0">
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
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 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 .
