.\" Copyright (c) 2001-2003 The Open Group, All Rights Reserved 
.TH "ECHO" 1P 2003 "IEEE/The Open Group" "POSIX Programmer's Manual"
.\" echo 
.SH 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.
.SH NAME
echo \- write arguments to standard output
.SH SYNOPSIS
.LP
\fBecho\fP \fB[\fP\fIstring\fP \fB...\fP\fB]\fP
.SH DESCRIPTION
.LP
The \fIecho\fP utility writes its arguments to standard output, followed
by a <newline>. If there are no arguments, only
the <newline> is written.
.SH OPTIONS
.LP
The \fIecho\fP utility shall not recognize the \fB"--"\fP 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; \fB"--"\fP shall be recognized as a string operand.
.LP
Implementations shall not support any options.
.SH OPERANDS
.LP
The following operands shall be supported:
.TP 7
\fIstring\fP
A string to be written to standard output. If the first operand is
\fB-n\fP, or if any of the operands contain a backslash (
\fB'\\'\fP ) character, the results are implementation-defined. 
.LP
On XSI-conformant systems, if the first operand is \fB-n\fP, 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:
.TP 7
\fB\\a\fP
.RS
Write an <alert>.
.RE
.TP 7
\fB\\b\fP
.RS
Write a <backspace>.
.RE
.TP 7
\fB\\c\fP
.RS
Suppress the <newline> that otherwise follows the final argument in
the output. All characters following the
\fB'\\c'\fP in the arguments shall be ignored.
.RE
.TP 7
\fB\\f\fP
.RS
Write a <form-feed>.
.RE
.TP 7
\fB\\n\fP
.RS
Write a <newline>.
.RE
.TP 7
\fB\\r\fP
.RS
Write a <carriage-return>.
.RE
.TP 7
\fB\\t\fP
.RS
Write a <tab>.
.RE
.TP 7
\fB\\v\fP
.RS
Write a <vertical-tab>.
.RE
.TP 7
\fB\\\\\fP
.RS
Write a backslash character.
.RE
.TP 7
\fB\\0\fP\fInum\fP
.RS
Write an 8-bit value that is the zero, one, two, or three-digit octal
number \fInum\fP.
.RE
.sp
.sp
.SH STDIN
.LP
Not used.
.SH INPUT FILES
.LP
None.
.SH ENVIRONMENT VARIABLES
.LP
The following environment variables shall affect the execution of
\fIecho\fP:
.TP 7
\fILANG\fP
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.)
.TP 7
\fILC_ALL\fP
If set to a non-empty string value, override the values of all the
other internationalization variables.
.TP 7
\fILC_CTYPE\fP
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). 
.TP 7
\fILC_MESSAGES\fP
Determine the locale that should be used to affect the format and
contents of diagnostic messages written to standard
error.
.TP 7
\fINLSPATH\fP
Determine the location of message catalogs for the processing of \fILC_MESSAGES
\&.\fP 
.sp
.SH ASYNCHRONOUS EVENTS
.LP
Default.
.SH STDOUT
.LP
The \fIecho\fP 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. 
.SH STDERR
.LP
The standard error shall be used only for diagnostic messages.
.SH OUTPUT FILES
.LP
None.
.SH EXTENDED DESCRIPTION
.LP
None.
.SH EXIT STATUS
.LP
The following exit values shall be returned:
.TP 7
\ 0
Successful completion.
.TP 7
>0
An error occurred.
.sp
.SH CONSEQUENCES OF ERRORS
.LP
Default.
.LP
\fIThe following sections are informative.\fP
.SH APPLICATION USAGE
.LP
It is not possible to use \fIecho\fP portably across all POSIX systems
unless both \fB-n\fP (as the first argument) and escape
sequences are omitted.
.LP
The \fIprintf\fP utility can be used portably to emulate any of the
traditional
behaviors of the \fIecho\fP utility as follows (assuming that \fIIFS\fP
has its standard value or is unset):
.IP " *" 3
The historic System V \fIecho\fP and the requirements on XSI implementations
in this volume of IEEE\ Std\ 1003.1-2001
are equivalent to:
.sp
.RS
.nf

\fBprintf "%b\\n" "$*"
\fP
.fi
.RE
.LP
.IP " *" 3
The BSD \fIecho\fP is equivalent to:
.sp
.RS
.nf

\fBif [ "X$1" = "X-n" ]
then
    shift
    printf "%s" "$*"
else
    printf "%s\\n" "$*"
fi
\fP
.fi
.RE
.LP
.LP
New applications are encouraged to use \fIprintf\fP instead of \fIecho\fP.
.SH EXAMPLES
.LP
None.
.SH RATIONALE
.LP
The \fIecho\fP 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 \fB-n\fP,
should use the \fIprintf\fP utility derived from the Ninth Edition
system.
.LP
As specified, \fIecho\fP writes its arguments in the simplest of ways.
The two different historical versions of \fIecho\fP
vary in fatally incompatible ways.
.LP
The BSD \fIecho\fP checks the first argument for the string \fB-n\fP
which causes it to suppress the <newline> that
would otherwise follow the final argument in the output.
.LP
The System V \fIecho\fP does not support any options, but allows escape
sequences within its operands, as described for XSI
implementations in the OPERANDS section.
.LP
The \fIecho\fP utility does not support Utility Syntax Guideline 10
because historical applications depend on \fIecho\fP to
echo \fIall\fP of its arguments, except for the \fB-n\fP option in
the BSD version.
.SH FUTURE DIRECTIONS
.LP
None.
.SH SEE ALSO
.LP
\fIprintf\fP
.SH 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 .
