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<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN"><html><head><meta name="generator" content="HTML Tidy, see www.w3.org"><meta http-equiv="Content-Type" content="text/html; charset=iso-8859-1"><link type="text/css" rel="stylesheet" href="style.css"><!-- Generated by The Open Group's rhtm tool v1.2.1 --><!-- Copyright (c) 2001-2003 The Open Group, All Rights Reserved --><title>echo</title></head><body bgcolor="white"><script type="text/javascript" language="JavaScript" src="../jscript/codes.js"></script><basefont size="3"> <a name="echo"></a> <a name="tag_04_41"></a><!-- echo --> <!--header start--><center><font size="2">The Open Group Base Specifications Issue 6<br>IEEE Std 1003.1, 2003 Edition<br>Copyright © 2001-2003 The IEEE and The Open Group, All Rights reserved.</font></center><!--header end--><hr size="2" noshade><h4><a name="tag_04_41_01"></a>NAME</h4><blockquote>echo - write arguments to standard output</blockquote><h4><a name="tag_04_41_02"></a>SYNOPSIS</h4><blockquote class="synopsis"><p><code><tt>echo</tt> <b>[</b><i>string</i> <tt>...</tt><b>]</b></code></p></blockquote><h4><a name="tag_04_41_03"></a>DESCRIPTION</h4><blockquote><p>The <i>echo</i> utility writes its arguments to standard output, followed by a <newline>. If there are no arguments, onlythe <newline> is written.</p></blockquote><h4><a name="tag_04_41_04"></a>OPTIONS</h4><blockquote><p>The <i>echo</i> utility shall not recognize the <tt>"--"</tt> argument in the manner specified by Guideline 10 of the BaseDefinitions volume of IEEE Std 1003.1-2001, <a href="../basedefs/xbd_chap12.html#tag_12_02">Section 12.2, Utility SyntaxGuidelines</a>; <tt>"--"</tt> shall be recognized as a string operand.</p><p>Implementations shall not support any options.</p></blockquote><h4><a name="tag_04_41_05"></a>OPERANDS</h4><blockquote><p>The following operands shall be supported:</p><dl compact><dt><i>string</i></dt><dd>A string to be written to standard output. If the first operand is <b>-n</b>, or if any of the operands contain a backslash (<tt>'\'</tt> ) character, the results are implementation-defined. <p><sup>[<a href="javascript:open_code('XSI')">XSI</a>]</sup> <img src="../images/opt-start.gif" alt="[Option Start]" border="0">On XSI-conformant systems, if the first operand is <b>-n</b>, it shall be treated as a string, not an option. The followingcharacter sequences shall be recognized on XSI-conformant systems within any of the arguments:</p><dl compact><dt><tt>\a</tt></dt><dd>Write an <alert>.</dd><dt><tt>\b</tt></dt><dd>Write a <backspace>.</dd><dt><tt>\c</tt></dt><dd>Suppress the <newline> that otherwise follows the final argument in the output. All characters following the<tt>'\c'</tt> in the arguments shall be ignored.</dd><dt><tt>\f</tt></dt><dd>Write a <form-feed>.</dd><dt><tt>\n</tt></dt><dd>Write a <newline>.</dd><dt><tt>\r</tt></dt><dd>Write a <carriage-return>.</dd><dt><tt>\t</tt></dt><dd>Write a <tab>.</dd><dt><tt>\v</tt></dt><dd>Write a <vertical-tab>.</dd><dt><tt>\\</tt></dt><dd>Write a backslash character.</dd><dt><tt>\0</tt><i>num</i></dt><dd>Write an 8-bit value that is the zero, one, two, or three-digit octal number <i>num</i>.</dd></dl></dd></dl><img src="../images/opt-end.gif" alt="[Option End]" border="0"></blockquote><h4><a name="tag_04_41_06"></a>STDIN</h4><blockquote><p>Not used.</p></blockquote><h4><a name="tag_04_41_07"></a>INPUT FILES</h4><blockquote><p>None.</p></blockquote><h4><a name="tag_04_41_08"></a>ENVIRONMENT VARIABLES</h4><blockquote><p>The following environment variables shall affect the execution of <i>echo</i>:</p><dl compact><dt><i>LANG</i></dt><dd>Provide a default value for the internationalization variables that are unset or null. (See the Base Definitions volume ofIEEE Std 1003.1-2001, <a href="../basedefs/xbd_chap08.html#tag_08_02">Section 8.2, Internationalization Variables</a> forthe precedence of internationalization variables used to determine the values of locale categories.)</dd><dt><i>LC_ALL</i></dt><dd>If set to a non-empty string value, override the values of all the other internationalization variables.</dd><dt><i>LC_CTYPE</i></dt><dd><sup>[<a href="javascript:open_code('XSI')">XSI</a>]</sup> <img src="../images/opt-start.gif" alt="[Option Start]" border="0">Determine the locale for the interpretation of sequences of bytes of text data as characters (for example, single-byte as opposedto multi-byte characters in arguments). <img src="../images/opt-end.gif" alt="[Option End]" border="0"></dd><dt><i>LC_MESSAGES</i></dt><dd>Determine the locale that should be used to affect the format and contents of diagnostic messages written to standarderror.</dd><dt><i>NLSPATH</i></dt><dd><sup>[<a href="javascript:open_code('XSI')">XSI</a>]</sup> <img src="../images/opt-start.gif" alt="[Option Start]" border="0">Determine the location of message catalogs for the processing of <i>LC_MESSAGES .</i> <img src="../images/opt-end.gif" alt="[Option End]" border="0"></dd></dl></blockquote><h4><a name="tag_04_41_09"></a>ASYNCHRONOUS EVENTS</h4><blockquote><p>Default.</p></blockquote><h4><a name="tag_04_41_10"></a>STDOUT</h4><blockquote><p>The <i>echo</i> utility arguments shall be separated by single <space>s and a <newline> shall follow the lastargument. <sup>[<a href="javascript:open_code('XSI')">XSI</a>]</sup> <img src="../images/opt-start.gif" alt="[Option Start]"border="0"> Output transformations shall occur based on the escape sequences in the input. See the OPERANDS section. <imgsrc="../images/opt-end.gif" alt="[Option End]" border="0"></p></blockquote><h4><a name="tag_04_41_11"></a>STDERR</h4><blockquote><p>The standard error shall be used only for diagnostic messages.</p></blockquote><h4><a name="tag_04_41_12"></a>OUTPUT FILES</h4><blockquote><p>None.</p></blockquote><h4><a name="tag_04_41_13"></a>EXTENDED DESCRIPTION</h4><blockquote><p>None.</p></blockquote><h4><a name="tag_04_41_14"></a>EXIT STATUS</h4><blockquote><p>The following exit values shall be returned:</p><dl compact><dt> 0</dt><dd>Successful completion.</dd><dt>>0</dt><dd>An error occurred.</dd></dl></blockquote><h4><a name="tag_04_41_15"></a>CONSEQUENCES OF ERRORS</h4><blockquote><p>Default.</p></blockquote><hr><div class="box"><em>The following sections are informative.</em></div><h4><a name="tag_04_41_16"></a>APPLICATION USAGE</h4><blockquote><p>It is not possible to use <i>echo</i> portably across all POSIX systems unless both <b>-n</b> (as the first argument) and escapesequences are omitted.</p><p>The <a href="../utilities/printf.html"><i>printf</i></a> utility can be used portably to emulate any of the traditionalbehaviors of the <i>echo</i> utility as follows (assuming that <i>IFS</i> has its standard value or is unset):</p><ul><li><p>The historic System V <i>echo</i> and the requirements on XSI implementations in this volume of IEEE Std 1003.1-2001are equivalent to:</p><pre><tt>printf "%b\n" "$*"</tt></pre></li><li><p>The BSD <i>echo</i> is equivalent to:</p><pre><tt>if [ "X$1" = "X-n" ]then shift printf "%s" "$*"else printf "%s\n" "$*"fi</tt></pre></li></ul><p>New applications are encouraged to use <a href="../utilities/printf.html"><i>printf</i></a> instead of <i>echo</i>.</p></blockquote><h4><a name="tag_04_41_17"></a>EXAMPLES</h4><blockquote><p>None.</p></blockquote><h4><a name="tag_04_41_18"></a>RATIONALE</h4><blockquote><p>The <i>echo</i> 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 <b>-n</b>,should use the <a href="../utilities/printf.html"><i>printf</i></a> utility derived from the Ninth Edition system.</p><p>As specified, <i>echo</i> writes its arguments in the simplest of ways. The two different historical versions of <i>echo</i>vary in fatally incompatible ways.</p><p>The BSD <i>echo</i> checks the first argument for the string <b>-n</b> which causes it to suppress the <newline> thatwould otherwise follow the final argument in the output.</p><p>The System V <i>echo</i> does not support any options, but allows escape sequences within its operands, as described for XSIimplementations in the OPERANDS section.</p><p>The <i>echo</i> utility does not support Utility Syntax Guideline 10 because historical applications depend on <i>echo</i> toecho <i>all</i> of its arguments, except for the <b>-n</b> option in the BSD version.</p></blockquote><h4><a name="tag_04_41_19"></a>FUTURE DIRECTIONS</h4><blockquote><p>None.</p></blockquote><h4><a name="tag_04_41_20"></a>SEE ALSO</h4><blockquote><p><a href="printf.html"><i>printf</i></a></p></blockquote><h4><a name="tag_04_41_21"></a>CHANGE HISTORY</h4><blockquote><p>First released in Issue 2.</p></blockquote><h4><a name="tag_04_41_22"></a>Issue 5</h4><blockquote><p>In the OPTIONS section, the last sentence is changed to indicate that implementations "do not" support any options; in theprevious issue this said "need not".</p></blockquote><h4><a name="tag_04_41_23"></a>Issue 6</h4><blockquote><p>The following new requirements on POSIX implementations derive from alignment with the Single UNIX Specification:</p><ul><li><p>A set of character sequences is defined as <i>string</i> operands.</p></li><li><p><i>LC_CTYPE</i> is added to the list of environment variables affecting <i>echo</i>.</p></li><li><p>In the OPTIONS section, implementations shall not support any options.</p></li></ul><p>IEEE Std 1003.1-2001/Cor 1-2002, item XCU/TC1/D6/21 is applied, so that the <i>echo</i> utility can accommodatehistorical BSD behavior.</p></blockquote><div class="box"><em>End of informative text.</em></div><hr><hr size="2" noshade><center><font size="2"><!--footer start-->UNIX ® is a registered Trademark of The Open Group.<br>POSIX ® is a registered Trademark of The IEEE.<br>[ <a href="../mindex.html">Main Index</a> | <a href="../basedefs/contents.html">XBD</a> | <a href="../utilities/contents.html">XCU</a> | <a href="../functions/contents.html">XSH</a> | <a href="../xrat/contents.html">XRAT</a>]</font></center><!--footer end--><hr size="2" noshade></body></html>⌨️ 快捷键说明
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