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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>head</title></head><body bgcolor="white"><script type="text/javascript" language="JavaScript" src="../jscript/codes.js"></script><basefont size="3"> <a name="head"></a> <a name="tag_04_65"></a><!-- head --> <!--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_65_01"></a>NAME</h4><blockquote>head - copy the first part of files</blockquote><h4><a name="tag_04_65_02"></a>SYNOPSIS</h4><blockquote class="synopsis"><p><code><tt>head</tt> <b>[</b><tt>-n</tt> <i>number</i><b>][</b><i>file</i><tt>...</tt><b>]</b></code></p></blockquote><h4><a name="tag_04_65_03"></a>DESCRIPTION</h4><blockquote><p>The <i>head</i> utility shall copy its input files to the standard output, ending the output for each file at a designatedpoint.</p><p>Copying shall end at the point in each input file indicated by the <b>-n</b> <i>number</i> option. The option-argument<i>number</i> shall be counted in units of lines.</p></blockquote><h4><a name="tag_04_65_04"></a>OPTIONS</h4><blockquote><p>The <i>head</i> utility shall conform to the Base Definitions volume of IEEE Std 1003.1-2001, <a href="../basedefs/xbd_chap12.html#tag_12_02">Section 12.2, Utility Syntax Guidelines</a>.</p><p>The following option shall be supported:</p><dl compact><dt><b>-n </b> <i>number</i></dt><dd>The first <i>number</i> lines of each input file shall be copied to standard output. The application shall ensure that the<i>number</i> option-argument is a positive decimal integer.</dd></dl><p>When a file contains less than <i>number</i> lines, it shall be copied to standard output in its entirety. This shall not be anerror.</p><p>If no options are specified, <i>head</i> shall act as if <b>-n 10</b> had been specified.</p></blockquote><h4><a name="tag_04_65_05"></a>OPERANDS</h4><blockquote><p>The following operand shall be supported:</p><dl compact><dt><i>file</i></dt><dd>A pathname of an input file. If no <i>file</i> operands are specified, the standard input shall be used.</dd></dl></blockquote><h4><a name="tag_04_65_06"></a>STDIN</h4><blockquote><p>The standard input shall be used only if no <i>file</i> operands are specified. See the INPUT FILES section.</p></blockquote><h4><a name="tag_04_65_07"></a>INPUT FILES</h4><blockquote><p>Input files shall be text files, but the line length is not restricted to {LINE_MAX} bytes.</p></blockquote><h4><a name="tag_04_65_08"></a>ENVIRONMENT VARIABLES</h4><blockquote><p>The following environment variables shall affect the execution of <i>head</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>Determine the locale for the interpretation of sequences of bytes of text data as characters (for example, single-byte asopposed to multi-byte characters in arguments and input files).</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_65_09"></a>ASYNCHRONOUS EVENTS</h4><blockquote><p>Default.</p></blockquote><h4><a name="tag_04_65_10"></a>STDOUT</h4><blockquote><p>The standard output shall contain designated portions of the input files.</p><p>If multiple <i>file</i> operands are specified, <i>head</i> shall precede the output for each with the header:</p><pre><tt>"\n==> %s <==\n", <</tt><i>pathname</i><tt>></tt></pre><p>except that the first header written shall not include the initial <newline>.</p></blockquote><h4><a name="tag_04_65_11"></a>STDERR</h4><blockquote><p>The standard error shall be used only for diagnostic messages.</p></blockquote><h4><a name="tag_04_65_12"></a>OUTPUT FILES</h4><blockquote><p>None.</p></blockquote><h4><a name="tag_04_65_13"></a>EXTENDED DESCRIPTION</h4><blockquote><p>None.</p></blockquote><h4><a name="tag_04_65_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_65_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_65_16"></a>APPLICATION USAGE</h4><blockquote><p>The obsolescent <b>-</b> <i>number</i> form is withdrawn in this version. Applications should use the <b>-n</b> <i>number</i>option.</p></blockquote><h4><a name="tag_04_65_17"></a>EXAMPLES</h4><blockquote><p>To write the first ten lines of all files (except those with a leading period) in the directory:</p><pre><tt>head *</tt></pre></blockquote><h4><a name="tag_04_65_18"></a>RATIONALE</h4><blockquote><p>Although it is possible to simulate <i>head</i> with <a href="../utilities/sed.html"><i>sed</i></a> 10q for a single file, thestandard developers decided that the popularity of <i>head</i> on historical BSD systems warranted its inclusion alongside <a href="../utilities/tail.html"><i>tail</i></a>.</p><p>This standard version of <i>head</i> follows the Utility Syntax Guidelines. The <b>-n</b> option was added to this new interfaceso that <i>head</i> and <a href="../utilities/tail.html"><i>tail</i></a> would be more logically related.</p><p>There is no <b>-c</b> option (as there is in <a href="../utilities/tail.html"><i>tail</i></a>) because it is not historicalpractice and because other utilities in this volume of IEEE Std 1003.1-2001 provide similar functionality.</p></blockquote><h4><a name="tag_04_65_19"></a>FUTURE DIRECTIONS</h4><blockquote><p>None.</p></blockquote><h4><a name="tag_04_65_20"></a>SEE ALSO</h4><blockquote><p><a href="sed.html"><i>sed</i></a> , <a href="tail.html"><i>tail</i></a></p></blockquote><h4><a name="tag_04_65_21"></a>CHANGE HISTORY</h4><blockquote><p>First released in Issue 4.</p></blockquote><h4><a name="tag_04_65_22"></a>Issue 6</h4><blockquote><p>The obsolescent <b>-number</b> form is withdrawn.</p><p>The normative text is reworded to avoid use of the term "must" for application requirements.</p><p>The DESCRIPTION is updated to clarify that when a file contains less than the number of lines requested, the entire file iscopied to standard output.</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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