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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>cat</title></head><body bgcolor="white"><script type="text/javascript" language="JavaScript" src="../jscript/codes.js"></script><basefont size="3"> <a name="cat"></a> <a name="tag_04_14"></a><!-- cat --> <!--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_14_01"></a>NAME</h4><blockquote>cat - concatenate and print files</blockquote><h4><a name="tag_04_14_02"></a>SYNOPSIS</h4><blockquote class="synopsis"><p><code><tt>cat</tt> <b>[</b><tt>-u</tt><b>][</b><i>file</i> <tt>...</tt><b>]</b></code></p></blockquote><h4><a name="tag_04_14_03"></a>DESCRIPTION</h4><blockquote><p>The <i>cat</i> utility shall read files in sequence and shall write their contents to the standard output in the samesequence.</p></blockquote><h4><a name="tag_04_14_04"></a>OPTIONS</h4><blockquote><p>The <i>cat</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>-u</b></dt><dd>Write bytes from the input file to the standard output without delay as each is read.</dd></dl></blockquote><h4><a name="tag_04_14_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. If a <i>file</i> is<tt>'-'</tt> , the <i>cat</i> utility shall read from the standard input at that point in the sequence. The <i>cat</i> utilityshall not close and reopen standard input when it is referenced in this way, but shall accept multiple occurrences of <tt>'-'</tt>as a <i>file</i> operand.</dd></dl></blockquote><h4><a name="tag_04_14_06"></a>STDIN</h4><blockquote><p>The standard input shall be used only if no <i>file</i> operands are specified, or if a <i>file</i> operand is <tt>'-'</tt> .See the INPUT FILES section.</p></blockquote><h4><a name="tag_04_14_07"></a>INPUT FILES</h4><blockquote><p>The input files can be any file type.</p></blockquote><h4><a name="tag_04_14_08"></a>ENVIRONMENT VARIABLES</h4><blockquote><p>The following environment variables shall affect the execution of <i>cat</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).</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_14_09"></a>ASYNCHRONOUS EVENTS</h4><blockquote><p>Default.</p></blockquote><h4><a name="tag_04_14_10"></a>STDOUT</h4><blockquote><p>The standard output shall contain the sequence of bytes read from the input files. Nothing else shall be written to the standardoutput.</p></blockquote><h4><a name="tag_04_14_11"></a>STDERR</h4><blockquote><p>The standard error shall be used only for diagnostic messages.</p></blockquote><h4><a name="tag_04_14_12"></a>OUTPUT FILES</h4><blockquote><p>None.</p></blockquote><h4><a name="tag_04_14_13"></a>EXTENDED DESCRIPTION</h4><blockquote><p>None.</p></blockquote><h4><a name="tag_04_14_14"></a>EXIT STATUS</h4><blockquote><p>The following exit values shall be returned:</p><dl compact><dt> 0</dt><dd>All input files were output successfully.</dd><dt>>0</dt><dd>An error occurred.</dd></dl></blockquote><h4><a name="tag_04_14_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_14_16"></a>APPLICATION USAGE</h4><blockquote><p>The <b>-u</b> option has value in prototyping non-blocking reads from FIFOs. The intent is to support the followingsequence:</p><pre><tt>mkfifo foocat -u foo > /dev/tty13 &cat -u > foo</tt></pre><p>It is unspecified whether standard output is or is not buffered in the default case. This is sometimes of interest when standardoutput is associated with a terminal, since buffering may delay the output. The presence of the <b>-u</b> option guarantees thatunbuffered I/O is available. It is implementation-defined whether the <i>cat</i> utility buffers output if the <b>-u</b> option isnot specified. Traditionally, the <b>-u</b> option is implemented using the equivalent of the <a href="../functions/setvbuf.html"><i>setvbuf</i>()</a> function defined in the System Interfaces volume ofIEEE Std 1003.1-2001.</p></blockquote><h4><a name="tag_04_14_17"></a>EXAMPLES</h4><blockquote><p>The following command:</p><pre><tt>cat myfile</tt></pre><p>writes the contents of the file <b>myfile</b> to standard output.</p><p>The following command:</p><pre><tt>cat doc1 doc2 > doc.all</tt></pre><p>concatenates the files <b>doc1</b> and <b>doc2</b> and writes the result to <b>doc.all</b>.</p><p>Because of the shell language mechanism used to perform output redirection, a command such as this:</p><pre><tt>cat doc doc.end > doc</tt></pre><p>causes the original data in <b>doc</b> to be lost.</p><p>The command:</p><pre><tt>cat start - middle - end > file</tt></pre><p>when standard input is a terminal, gets two arbitrary pieces of input from the terminal with a single invocation of <i>cat</i>.Note, however, that if standard input is a regular file, this would be equivalent to the command:</p><pre><tt>cat start - middle /dev/null end > file</tt></pre><p>because the entire contents of the file would be consumed by <i>cat</i> the first time <tt>'-'</tt> was used as a <i>file</i>operand and an end-of-file condition would be detected immediately when <tt>'-'</tt> was referenced the second time.</p></blockquote><h4><a name="tag_04_14_18"></a>RATIONALE</h4><blockquote><p>Historical versions of the <i>cat</i> utility include the options <b>-e</b>, <b>-t</b>, and <b>-v</b>, which permit the ends oflines, <tab>s, and invisible characters, respectively, to be rendered visible in the output. The standard developers omittedthese options because they provide too fine a degree of control over what is made visible, and similar output can be obtained usinga command such as:</p><pre><tt>sed -n -e 's/$/$/' -e l pathname</tt></pre><p>The <b>-s</b> option was omitted because it corresponds to different functions in BSD and System V-based systems. The BSD<b>-s</b> option to squeeze blank lines can be accomplished by the shell script shown in the following example:</p><pre><tt>sed -n '# Write non-empty lines././ { p d }# Write a single empty line, then look for more empty lines./^$/ p# Get next line, discard the held <newline> (empty line),# and look for more empty lines.:Empty/^$/ { N s/.// b Empty }# Write the non-empty line before going back to search# for the first in a set of empty lines. p'</tt></pre><p>The System V <b>-s</b> option to silence error messages can be accomplished by redirecting the standard error. Note that the BSDdocumentation for <i>cat</i> uses the term "blank line" to mean the same as the POSIX "empty line'': a line consisting only of a<newline>.</p><p>The BSD <b>-n</b> option was omitted because similar functionality can be obtained from the <b>-n</b> option of the <a href="../utilities/pr.html"><i>pr</i></a> utility.</p></blockquote><h4><a name="tag_04_14_19"></a>FUTURE DIRECTIONS</h4><blockquote><p>None.</p></blockquote><h4><a name="tag_04_14_20"></a>SEE ALSO</h4><blockquote><p><a href="more.html"><i>more</i></a> , the System Interfaces volume of IEEE Std 1003.1-2001, <a href="../functions/setvbuf.html"><i>setvbuf</i>()</a></p></blockquote><h4><a name="tag_04_14_21"></a>CHANGE HISTORY</h4><blockquote><p>First released in Issue 2.</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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