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22 <script language="JavaScript" src="../jscript/codes.js"></script><basefont size="3">
23 <center><font size="2">The Open Group Base Specifications Issue 8<br>
24 IEEE Std 1003.1-2024<br>
25 Copyright © 2001-2024 The IEEE and The Open Group</font></center>
26 <hr size="2" noshade>
27 <a name="top" id="top"></a> <a name="cat" id="cat"></a> <a name="tag_20_13" id="tag_20_13"></a><!-- cat -->
28 <h4 class="mansect"><a name="tag_20_13_01" id="tag_20_13_01"></a>NAME</h4>
29 <blockquote>cat — concatenate and print files</blockquote>
30 <h4 class="mansect"><a name="tag_20_13_02" id="tag_20_13_02"></a>SYNOPSIS</h4>
31 <blockquote class="synopsis">
32 <p><code><tt>cat</tt> <b>[</b><tt>-u</tt><b>] [</b><i>file</i><tt>...</tt><b>]</b></code></p>
33 </blockquote>
34 <h4 class="mansect"><a name="tag_20_13_03" id="tag_20_13_03"></a>DESCRIPTION</h4>
35 <blockquote>
36 <p>The <i>cat</i> utility shall read files in sequence and shall write their contents to the standard output in the same
37 sequence.</p>
38 </blockquote>
39 <h4 class="mansect"><a name="tag_20_13_04" id="tag_20_13_04"></a>OPTIONS</h4>
40 <blockquote>
41 <p>The <i>cat</i> utility shall conform to XBD <a href="../basedefs/V1_chap12.html#tag_12_02"><i>12.2 Utility Syntax
42 Guidelines</i></a> .</p>
43 <p>The following option shall be supported:</p>
44 <dl compact>
45 <dd></dd>
46 <dt><b>-u</b></dt>
47 <dd>Write bytes from the input file to the standard output without delay as each is read.</dd>
48 </dl>
49 </blockquote>
50 <h4 class="mansect"><a name="tag_20_13_05" id="tag_20_13_05"></a>OPERANDS</h4>
51 <blockquote>
52 <p>The following operand shall be supported:</p>
53 <dl compact>
54 <dd></dd>
55 <dt><i>file</i></dt>
56 <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
57 <tt>'-'</tt>, the <i>cat</i> utility shall read from the standard input at that point in the sequence. The <i>cat</i> utility shall
58 not close and reopen standard input when it is referenced in this way, but shall accept multiple occurrences of <tt>'-'</tt> as a
59 <i>file</i> operand.</dd>
60 </dl>
61 </blockquote>
62 <h4 class="mansect"><a name="tag_20_13_06" id="tag_20_13_06"></a>STDIN</h4>
63 <blockquote>
64 <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
65 the INPUT FILES section.</p>
66 </blockquote>
67 <h4 class="mansect"><a name="tag_20_13_07" id="tag_20_13_07"></a>INPUT FILES</h4>
68 <blockquote>
69 <p>The input files can be any file type.</p>
70 </blockquote>
71 <h4 class="mansect"><a name="tag_20_13_08" id="tag_20_13_08"></a>ENVIRONMENT VARIABLES</h4>
72 <blockquote>
73 <p>The following environment variables shall affect the execution of <i>cat</i>:</p>
74 <dl compact>
75 <dd></dd>
76 <dt><i>LANG</i></dt>
77 <dd>Provide a default value for the internationalization variables that are unset or null. (See XBD <a href=
78 "../basedefs/V1_chap08.html#tag_08_02"><i>8.2 Internationalization Variables</i></a> for the precedence of internationalization
79 variables used to determine the values of locale categories.)</dd>
80 <dt><i>LC_ALL</i></dt>
81 <dd>If set to a non-empty string value, override the values of all the other internationalization variables.</dd>
82 <dt><i>LC_CTYPE</i></dt>
83 <dd>Determine the locale for the interpretation of sequences of bytes of text data as characters (for example, single-byte as
84 opposed to multi-byte characters in arguments).</dd>
85 <dt><i>LC_MESSAGES</i></dt>
86 <dd><br>
87 Determine the locale that should be used to affect the format and contents of diagnostic messages written to standard error.</dd>
88 <dt><i>NLSPATH</i></dt>
89 <dd><sup>[<a href="javascript:open_code('XSI')">XSI</a>]</sup> <img src="../images/opt-start.gif" alt="[Option Start]" border="0">
90 Determine the location of messages objects and message catalogs. <img src="../images/opt-end.gif" alt="[Option End]" border=
91 "0"></dd>
92 </dl>
93 </blockquote>
94 <h4 class="mansect"><a name="tag_20_13_09" id="tag_20_13_09"></a>ASYNCHRONOUS EVENTS</h4>
95 <blockquote>
96 <p>Default.</p>
97 </blockquote>
98 <h4 class="mansect"><a name="tag_20_13_10" id="tag_20_13_10"></a>STDOUT</h4>
99 <blockquote>
100 <p>The standard output shall contain the sequence of bytes read from the input files. Nothing else shall be written to the standard
101 output. If the standard output is a regular file, and is the same file as any of the input file operands, the implementation may
102 treat this as an error.</p>
103 </blockquote>
104 <h4 class="mansect"><a name="tag_20_13_11" id="tag_20_13_11"></a>STDERR</h4>
105 <blockquote>
106 <p>The standard error shall be used only for diagnostic messages.</p>
107 </blockquote>
108 <h4 class="mansect"><a name="tag_20_13_12" id="tag_20_13_12"></a>OUTPUT FILES</h4>
109 <blockquote>
110 <p>None.</p>
111 </blockquote>
112 <h4 class="mansect"><a name="tag_20_13_13" id="tag_20_13_13"></a>EXTENDED DESCRIPTION</h4>
113 <blockquote>
114 <p>None.</p>
115 </blockquote>
116 <h4 class="mansect"><a name="tag_20_13_14" id="tag_20_13_14"></a>EXIT STATUS</h4>
117 <blockquote>
118 <p>The following exit values shall be returned:</p>
119 <dl compact>
120 <dd></dd>
121 <dt> 0</dt>
122 <dd>All input files were output successfully.</dd>
123 <dt>>0</dt>
124 <dd>An error occurred.</dd>
125 </dl>
126 </blockquote>
127 <h4 class="mansect"><a name="tag_20_13_15" id="tag_20_13_15"></a>CONSEQUENCES OF ERRORS</h4>
128 <blockquote>
129 <p>Default.</p>
130 </blockquote>
131 <hr>
132 <div class="box"><em>The following sections are informative.</em></div>
133 <h4 class="mansect"><a name="tag_20_13_16" id="tag_20_13_16"></a>APPLICATION USAGE</h4>
134 <blockquote>
135 <p>The <b>-u</b> option has value in prototyping non-blocking reads from FIFOs. The intent is to support the following
136 sequence:</p>
137 <pre>
138 <tt>mkfifo foo
139 cat -u foo > /dev/tty13 &
140 cat -u > foo
141 </tt></pre>
142 <p>It is unspecified whether standard output is or is not buffered in the default case. This is sometimes of interest when standard
143 output is associated with a terminal, since buffering may delay the output. The presence of the <b>-u</b> option guarantees that
144 unbuffered I/O is available. It is implementation-defined whether the <i>cat</i> utility buffers output if the <b>-u</b> option is
145 not specified. Traditionally, the <b>-u</b> option is implemented using the equivalent of the <a href=
146 "../functions/setvbuf.html"><i>setvbuf</i>()</a> function defined in the System Interfaces volume of POSIX.1-2024.</p>
147 </blockquote>
148 <h4 class="mansect"><a name="tag_20_13_17" id="tag_20_13_17"></a>EXAMPLES</h4>
149 <blockquote>
150 <p>The following command:</p>
151 <pre>
152 <tt>cat myfile
153 </tt></pre>
154 <p>writes the contents of the file <b>myfile</b> to standard output.</p>
155 <p>The following command:</p>
156 <pre>
157 <tt>cat doc1 doc2 > doc.all
158 </tt></pre>
159 <p>concatenates the files <b>doc1</b> and <b>doc2</b> and writes the result to <b>doc.all</b>.</p>
160 <p>Because of the shell language mechanism used to perform output redirection, a command such as this:</p>
161 <pre>
162 <tt>cat doc doc.end > doc
163 </tt></pre>
164 <p>causes the original data in <b>doc</b> to be lost before <i>cat</i> even begins execution. This is true whether the <i>cat</i>
165 command fails with an error or silently succeeds (the specification allows both behaviors). In order to append the contents of
166 <b>doc.end</b> without losing the original contents of <b>doc</b>, this command should be used instead:</p>
167 <pre>
168 <tt>cat doc.end >> doc
169 </tt></pre>
170 <p>The command:</p>
171 <pre>
172 <tt>cat start - middle - end > file
173 </tt></pre>
174 <p>when standard input is a terminal, gets two arbitrary pieces of input from the terminal with a single invocation of <i>cat</i>.
175 Note, however, that if standard input is a regular file, this would be equivalent to the command:</p>
176 <pre>
177 <tt>cat start - middle /dev/null end > file
178 </tt></pre>
179 <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>
180 operand and an end-of-file condition would be detected immediately when <tt>'-'</tt> was referenced the second time.</p>
181 </blockquote>
182 <h4 class="mansect"><a name="tag_20_13_18" id="tag_20_13_18"></a>RATIONALE</h4>
183 <blockquote>
184 <p>Historical versions of the <i>cat</i> utility include the <b>-e</b>, <b>-t</b>, and <b>-v</b>, options which permit the ends of
185 lines, <tab> characters, and invisible characters, respectively, to be rendered visible in the output. The standard
186 developers omitted these options because they provide too fine a degree of control over what is made visible, and similar output
187 can be obtained using a command such as:</p>
188 <pre>
189 <tt>sed -n l pathname
190 </tt></pre>
191 <p>The latter also has the advantage that its output is unambiguous, whereas the output of historical <i>cat</i> <b>-etv</b> is
192 not.</p>
193 <p>The <b>-s</b> option was omitted because it corresponds to different functions in BSD and System V-based systems. The BSD
194 <b>-s</b> option to squeeze blank lines can be accomplished by the shell script shown in the following example:</p>
195 <pre>
196 <tt>sed -n '
197 # Write non-empty lines.
198 /./ {
199 p
200 d
201 }
202 # Write a single empty line, then look for more empty lines.
203 /^$/ p
204 # Get next line, discard the held <newline> (empty line),
205 # and look for more empty lines.
206 :Empty
207 /^$/ {
208 N
209 s/.//
210 b Empty
211 }
212 # Write the non-empty line before going back to search
213 # for the first in a set of empty lines.
214 p
215 '
216 </tt></pre>
217 <p>The System V <b>-s</b> option to silence error messages can be accomplished by redirecting the standard error. Note that the BSD
218 documentation for <i>cat</i> uses the term "blank line" to mean the same as the POSIX "empty line": a line consisting only of a
219 <newline>.</p>
220 <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=
221 "../utilities/pr.html"><i>pr</i></a> utility.</p>
222 </blockquote>
223 <h4 class="mansect"><a name="tag_20_13_19" id="tag_20_13_19"></a>FUTURE DIRECTIONS</h4>
224 <blockquote>
225 <p>None.</p>
226 </blockquote>
227 <h4 class="mansect"><a name="tag_20_13_20" id="tag_20_13_20"></a>SEE ALSO</h4>
228 <blockquote>
229 <p><a href="../utilities/more.html#"><i>more</i></a></p>
230 <p>XBD <a href="../basedefs/V1_chap08.html#tag_08"><i>8. Environment Variables</i></a> , <a href=
231 "../basedefs/V1_chap12.html#tag_12_02"><i>12.2 Utility Syntax Guidelines</i></a></p>
232 <p>XSH <a href="../functions/setvbuf.html#"><i>setvbuf</i></a></p>
233 </blockquote>
234 <h4 class="mansect"><a name="tag_20_13_21" id="tag_20_13_21"></a>CHANGE HISTORY</h4>
235 <blockquote>
236 <p>First released in Issue 2.</p>
237 </blockquote>
238 <h4 class="mansect"><a name="tag_20_13_22" id="tag_20_13_22"></a>Issue 7</h4>
239 <blockquote>
240 <p>SD5-XCU-ERN-97 is applied, updating the SYNOPSIS.</p>
241 <p>SD5-XCU-ERN-174 is applied, changing the RATIONALE.</p>
242 <p>POSIX.1-2008, Technical Corrigendum 2, XCU/TC2-2008/0073 [876] is applied.</p>
243 </blockquote>
244 <h4 class="mansect"><a name="tag_20_13_23" id="tag_20_13_23"></a>Issue 8</h4>
245 <blockquote>
246 <p>Austin Group Defect 1122 is applied, changing the description of <i>NLSPATH .</i></p>
247 </blockquote>
248 <div class="box"><em>End of informative text.</em></div>
249 <hr>
250 <p> </p>
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