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echo(P) echo(P)
NAME
echo - write arguments to standard output
SYNOPSIS
echo [string ...]
DESCRIPTION
The echo utility writes its arguments to standard out-
put, 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 Def-
initions 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 fol-
lowing 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 fol-
lowing 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 internationaliza-
tion 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 cate-
gories.)
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 mes-
sages 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]" bor-
der="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 fol-
lows (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 applica-
tions. Conforming applications that wish to do prompt-
ing without <newline>s or that could possibly be expect-
ing 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 sec-
tion.
The echo utility does not support Utility Syntax Guide-
line 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 Operat-
ing System Interface (POSIX), The Open Group Base Speci-
fications Issue 6, Copyright (C) 2001-2003 by the Insti-
tute 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.open-
group.org/unix/online.html .
POSIX 2003 echo(P)
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