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.
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:
Write an <alert>.
Write a <backspace>.
Suppress the <newline> that otherwise
follows the final argument in the output. All characters following the
'\c' in the arguments shall be ignored.
Write a <form-feed>.
Write a <newline>.
Write a <carriage-return>.
Write a <tab>.
Write a <vertical-tab>.
Write a backslash character.
Write an 8-bit value that is the zero, one,
two, or three-digit octal number num.
The following environment variables shall affect the execution of echo:
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.)
If set to a non-empty string value, override the values of
all the other internationalization variables.
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).
Determine the locale that should be used to affect the
format and contents of diagnostic messages written to standard error.
Determine the location of message catalogs for the
processing of LC_MESSAGES.
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.
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:
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
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
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.
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