334 lines
9.5 KiB
HTML
334 lines
9.5 KiB
HTML
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<!-- Copyright (c) 2001 The Open Group, All Rights Reserved -->
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<title>echo</title>
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<basefont size="3"> <a name="echo"></a> <a name="tag_04_41"></a><!-- echo -->
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<!--header start-->
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<center><font size="2">The Open Group Base Specifications Issue 6<br>
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IEEE Std 1003.1-2001<br>
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Copyright © 2001 The IEEE and The Open Group, All Rights reserved.</font></center>
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<!--header end-->
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<hr size="2" noshade>
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<h4><a name="tag_04_41_01"></a>NAME</h4>
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<blockquote>echo - write arguments to standard output</blockquote>
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<h4><a name="tag_04_41_02"></a>SYNOPSIS</h4>
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<blockquote class="synopsis">
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<p><code><tt>echo</tt> <b>[</b><i>string</i> <tt>...</tt><b>]</b></code></p>
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</blockquote>
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<h4><a name="tag_04_41_03"></a>DESCRIPTION</h4>
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<blockquote>
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<p>The <i>echo</i> utility writes its arguments to standard output, followed by a <newline>. If there are no arguments, only
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the <newline> is written.</p>
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</blockquote>
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<h4><a name="tag_04_41_04"></a>OPTIONS</h4>
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<blockquote>
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<p>The <i>echo</i> utility shall not recognize the <tt>"--"</tt> argument in the manner specified by Guideline 10 of the Base
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Definitions volume of IEEE Std 1003.1-2001, <a href="../basedefs/xbd_chap12.html#tag_12_02">Section 12.2, Utility Syntax
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Guidelines</a>; <tt>"--"</tt> shall be recognized as a string operand.</p>
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<p>Implementations shall not support any options.</p>
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</blockquote>
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<h4><a name="tag_04_41_05"></a>OPERANDS</h4>
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<blockquote>
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<p>The following operands shall be supported:</p>
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<dl compact>
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<dt><i>string</i></dt>
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<dd>A string to be written to standard output. If any operand is <b>-n</b>, it shall be treated as a string, not an option. The
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following character sequences shall be recognized within any of the arguments:
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<dl compact>
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<dt><tt>\a</tt></dt>
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<dd>Write an <alert>.</dd>
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<dt><tt>\b</tt></dt>
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<dd>Write a <backspace>.</dd>
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<dt><tt>\c</tt></dt>
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<dd>Suppress the <newline> that otherwise follows the final argument in the output. All characters following the
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<tt>'\c'</tt> in the arguments shall be ignored.</dd>
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<dt><tt>\f</tt></dt>
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<dd>Write a <form-feed>.</dd>
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<dt><tt>\n</tt></dt>
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<dd>Write a <newline>.</dd>
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<dt><tt>\r</tt></dt>
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<dd>Write a <carriage-return>.</dd>
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<dt><tt>\t</tt></dt>
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<dd>Write a <tab>.</dd>
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<dt><tt>\v</tt></dt>
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<dd>Write a <vertical-tab>.</dd>
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<dt><tt>\\</tt></dt>
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<dd>Write a backslash character.</dd>
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<dt><tt>\0</tt><i>num</i></dt>
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<dd>Write an 8-bit value that is the zero, one, two, or three-digit octal number <i>num</i>.</dd>
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</dl>
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</dd>
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</dl>
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</blockquote>
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<h4><a name="tag_04_41_06"></a>STDIN</h4>
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<blockquote>
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<p>Not used.</p>
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</blockquote>
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<h4><a name="tag_04_41_07"></a>INPUT FILES</h4>
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<blockquote>
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<p>None.</p>
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</blockquote>
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<h4><a name="tag_04_41_08"></a>ENVIRONMENT VARIABLES</h4>
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<blockquote>
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<p>The following environment variables shall affect the execution of <i>echo</i>:</p>
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<dl compact>
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<dt><i>LANG</i></dt>
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<dd>Provide a default value for the internationalization variables that are unset or null. (See the Base Definitions volume of
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IEEE Std 1003.1-2001, <a href="../basedefs/xbd_chap08.html#tag_08_02">Section 8.2, Internationalization Variables</a> for
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the precedence of internationalization variables used to determine the values of locale categories.)</dd>
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<dt><i>LC_ALL</i></dt>
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<dd>If set to a non-empty string value, override the values of all the other internationalization variables.</dd>
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<dt><i>LC_CTYPE</i></dt>
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<dd>Determine the locale for the interpretation of sequences of bytes of text data as characters (for example, single-byte as
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opposed to multi-byte characters in arguments).</dd>
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<dt><i>LC_MESSAGES</i></dt>
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<dd>Determine the locale that should be used to affect the format and contents of diagnostic messages written to standard
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error.</dd>
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<dt><i>NLSPATH</i></dt>
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<dd><sup>[<a href="javascript:open_code('XSI')">XSI</a>]</sup> <img src="../images/opt-start.gif" alt="[Option Start]" border="0">
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Determine the location of message catalogs for the processing of <i>LC_MESSAGES .</i> <img src="../images/opt-end.gif" alt=
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"[Option End]" border="0"></dd>
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</dl>
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</blockquote>
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<h4><a name="tag_04_41_09"></a>ASYNCHRONOUS EVENTS</h4>
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<blockquote>
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<p>Default.</p>
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</blockquote>
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<h4><a name="tag_04_41_10"></a>STDOUT</h4>
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<blockquote>
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<p>The <i>echo</i> utility arguments shall be separated by single <space>s and a <newline> shall follow the last
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argument. Output transformations shall occur based on the escape sequences in the input. See the OPERANDS section.</p>
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</blockquote>
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<h4><a name="tag_04_41_11"></a>STDERR</h4>
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<blockquote>
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<p>The standard error shall be used only for diagnostic messages.</p>
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</blockquote>
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<h4><a name="tag_04_41_12"></a>OUTPUT FILES</h4>
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<blockquote>
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<p>None.</p>
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</blockquote>
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<h4><a name="tag_04_41_13"></a>EXTENDED DESCRIPTION</h4>
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<blockquote>
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<p>None.</p>
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</blockquote>
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<h4><a name="tag_04_41_14"></a>EXIT STATUS</h4>
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<blockquote>
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<p>The following exit values shall be returned:</p>
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<dl compact>
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<dt> 0</dt>
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<dd>Successful completion.</dd>
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<dt>>0</dt>
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<dd>An error occurred.</dd>
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</dl>
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</blockquote>
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<h4><a name="tag_04_41_15"></a>CONSEQUENCES OF ERRORS</h4>
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<blockquote>
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<p>Default.</p>
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</blockquote>
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<hr>
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<div class="box"><em>The following sections are informative.</em></div>
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<h4><a name="tag_04_41_16"></a>APPLICATION USAGE</h4>
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<blockquote>
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<p>In the ISO/IEC 9945-2:1993 standard, it was not possible to use <i>echo</i> portably across all systems that were not
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XSI-conformant unless both <b>-n</b> (as the first argument) and escape sequences were omitted.</p>
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<p>The <a href="../utilities/printf.html"><i>printf</i></a> utility can be used portably to emulate any of the traditional
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behaviors of the <i>echo</i> utility as follows (assuming that <i>IFS</i> has its standard value or is unset):</p>
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<ul>
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<li>
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<p>The historic System V <i>echo</i> and the current requirements in this volume of IEEE Std 1003.1-2001 are equivalent
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to:</p>
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<pre>
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<tt>printf "%b\n" "$*"
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</tt>
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</pre>
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</li>
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<li>
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<p>The BSD <i>echo</i> is equivalent to:</p>
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<pre>
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<tt>if [ "X$1" = "X-n" ]
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then
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shift
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printf "%s" "$*"
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else
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printf "%s\n" "$*"
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fi
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</tt>
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</pre>
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</li>
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</ul>
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<p>New applications are encouraged to use <a href="../utilities/printf.html"><i>printf</i></a> instead of <i>echo</i>.</p>
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</blockquote>
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<h4><a name="tag_04_41_17"></a>EXAMPLES</h4>
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<blockquote>
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<p>None.</p>
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</blockquote>
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<h4><a name="tag_04_41_18"></a>RATIONALE</h4>
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<blockquote>
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<p>The <i>echo</i> utility has not been made obsolescent because of its extremely widespread use in historical applications.
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Conforming applications that wish to do prompting without <newline>s or that could possibly be expecting to echo a <b>-n</b>,
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should use the <a href="../utilities/printf.html"><i>printf</i></a> utility derived from the Ninth Edition system.</p>
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<p>As specified, <i>echo</i> writes its arguments in the simplest of ways. The two different historical versions of <i>echo</i>
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vary in fatally incompatible ways.</p>
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<p>The BSD <i>echo</i> checks the first argument for the string <b>-n</b> which causes it to suppress the <newline> that
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would otherwise follow the final argument in the output.</p>
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<p>The System V <i>echo</i> does not support any options, but allows escape sequences within its operands, as described in the
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OPERANDS section.</p>
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<p>The <i>echo</i> utility does not support Utility Syntax Guideline 10 because historical applications depend on <i>echo</i> to
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echo <i>all</i> of its arguments, except for the <b>-n</b> option in the BSD version.</p>
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</blockquote>
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<h4><a name="tag_04_41_19"></a>FUTURE DIRECTIONS</h4>
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<blockquote>
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<p>None.</p>
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</blockquote>
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<h4><a name="tag_04_41_20"></a>SEE ALSO</h4>
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<blockquote>
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<p><a href="printf.html"><i>printf</i></a></p>
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</blockquote>
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<h4><a name="tag_04_41_21"></a>CHANGE HISTORY</h4>
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<blockquote>
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<p>First released in Issue 2.</p>
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</blockquote>
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<h4><a name="tag_04_41_22"></a>Issue 5</h4>
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<blockquote>
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<p>In the OPTIONS section, the last sentence is changed to indicate that implementations "do not" support any options; in the
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previous issue this said "need not".</p>
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</blockquote>
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<h4><a name="tag_04_41_23"></a>Issue 6</h4>
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<blockquote>
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<p>The following new requirements on POSIX implementations derive from alignment with the Single UNIX Specification:</p>
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<ul>
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<li>
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<p>A set of character sequences is defined as <i>string</i> operands.</p>
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</li>
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<li>
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<p><i>LC_CTYPE</i> is added to the list of environment variables affecting <i>echo</i>.</p>
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</li>
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<li>
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<p>In the OPTIONS section, implementations shall not support any options.</p>
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</li>
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</ul>
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</blockquote>
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<div class="box"><em>End of informative text.</em></div>
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<hr>
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<hr size="2" noshade>
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<center><font size="2"><!--footer start-->
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UNIX ® is a registered Trademark of The Open Group.<br>
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POSIX ® is a registered Trademark of The IEEE.<br>
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