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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="echo" id="echo"></a> <a name="tag_20_37" id="tag_20_37"></a><!-- echo -->
28 <h4 class="mansect"><a name="tag_20_37_01" id="tag_20_37_01"></a>NAME</h4>
29 <blockquote>echo — write arguments to standard output</blockquote>
30 <h4 class="mansect"><a name="tag_20_37_02" id="tag_20_37_02"></a>SYNOPSIS</h4>
31 <blockquote class="synopsis">
32 <p><code><tt>echo</tt> <b>[</b><i>string</i><tt>...</tt><b>]</b></code></p>
33 </blockquote>
34 <h4 class="mansect"><a name="tag_20_37_03" id="tag_20_37_03"></a>DESCRIPTION</h4>
35 <blockquote>
36 <p>The <i>echo</i> utility writes its arguments to standard output, followed by a <newline>. If there are no arguments, only
37 the <newline> is written.</p>
38 </blockquote>
39 <h4 class="mansect"><a name="tag_20_37_04" id="tag_20_37_04"></a>OPTIONS</h4>
40 <blockquote>
41 <p>The <i>echo</i> utility shall not recognize the <tt>"--"</tt> argument in the manner specified by Guideline 10 of XBD <a href=
42 "../basedefs/V1_chap12.html#tag_12_02"><i>12.2 Utility Syntax Guidelines</i></a> ; <tt>"--"</tt> shall be recognized as a string
43 operand.</p>
44 <p>Implementations shall not support any options.</p>
45 </blockquote>
46 <h4 class="mansect"><a name="tag_20_37_05" id="tag_20_37_05"></a>OPERANDS</h4>
47 <blockquote>
48 <p>The following operands shall be supported:</p>
49 <dl compact>
50 <dd></dd>
51 <dt><i>string</i></dt>
52 <dd>A string to be written to standard output. If the first operand consists of a <tt>'-'</tt> followed by one or more characters
53 from the set {<tt>'e'</tt>, <tt>'E'</tt>, <tt>'n'</tt>}, or if any of the operands contain a <backslash> character, the
54 results are implementation-defined.
55 <p><sup>[<a href="javascript:open_code('XSI')">XSI</a>]</sup> <img src="../images/opt-start.gif" alt="[Option Start]" border="0">
56 On XSI-conformant systems, if the first operand consists of a <tt>'-'</tt> followed by one or more characters from the set
57 {<tt>'e'</tt>, <tt>'E'</tt>, <tt>'n'</tt>}, it shall be treated as a string to be written. The following character sequences shall
58 be recognized on XSI-conformant systems within any of the arguments:</p>
59 <dl compact>
60 <dd></dd>
61 <dt><tt>\a</tt></dt>
62 <dd>Write an <alert>.</dd>
63 <dt><tt>\b</tt></dt>
64 <dd>Write a <backspace>.</dd>
65 <dt><tt>\c</tt></dt>
66 <dd>Suppress the <newline> that otherwise follows the final argument in the output. All characters following the
67 <tt>'\c'</tt> in the arguments shall be ignored.</dd>
68 <dt><tt>\f</tt></dt>
69 <dd>Write a <form-feed>.</dd>
70 <dt><tt>\n</tt></dt>
71 <dd>Write a <newline>.</dd>
72 <dt><tt>\r</tt></dt>
73 <dd>Write a <carriage-return>.</dd>
74 <dt><tt>\t</tt></dt>
75 <dd>Write a <tab>.</dd>
76 <dt><tt>\v</tt></dt>
77 <dd>Write a <vertical-tab>.</dd>
78 <dt><tt>\\</tt></dt>
79 <dd>Write a <backslash> character.</dd>
80 <dt><tt>\0</tt><i>num</i></dt>
81 <dd>Write an 8-bit value that is the zero, one, two, or three-digit octal number <i>num</i>.</dd>
82 </dl>
83 </dd>
84 </dl>
85 <img src="../images/opt-end.gif" alt="[Option End]" border="0"></blockquote>
86 <h4 class="mansect"><a name="tag_20_37_06" id="tag_20_37_06"></a>STDIN</h4>
87 <blockquote>
88 <p>Not used.</p>
89 </blockquote>
90 <h4 class="mansect"><a name="tag_20_37_07" id="tag_20_37_07"></a>INPUT FILES</h4>
91 <blockquote>
92 <p>None.</p>
93 </blockquote>
94 <h4 class="mansect"><a name="tag_20_37_08" id="tag_20_37_08"></a>ENVIRONMENT VARIABLES</h4>
95 <blockquote>
96 <p>The following environment variables shall affect the execution of <i>echo</i>:</p>
97 <dl compact>
98 <dd></dd>
99 <dt><i>LANG</i></dt>
100 <dd>Provide a default value for the internationalization variables that are unset or null. (See XBD <a href=
101 "../basedefs/V1_chap08.html#tag_08_02"><i>8.2 Internationalization Variables</i></a> for the precedence of internationalization
102 variables used to determine the values of locale categories.)</dd>
103 <dt><i>LC_ALL</i></dt>
104 <dd>If set to a non-empty string value, override the values of all the other internationalization variables.</dd>
105 <dt><i>LC_CTYPE</i></dt>
106 <dd><sup>[<a href="javascript:open_code('XSI')">XSI</a>]</sup> <img src="../images/opt-start.gif" alt="[Option Start]" border="0">
107 Determine the locale for the interpretation of sequences of bytes of text data as characters (for example, single-byte as opposed
108 to multi-byte characters in arguments). <img src="../images/opt-end.gif" alt="[Option End]" border="0"></dd>
109 <dt><i>LC_MESSAGES</i></dt>
110 <dd><br>
111 Determine the locale that should be used to affect the format and contents of diagnostic messages written to standard error.</dd>
112 <dt><i>NLSPATH</i></dt>
113 <dd><sup>[<a href="javascript:open_code('XSI')">XSI</a>]</sup> <img src="../images/opt-start.gif" alt="[Option Start]" border="0">
114 Determine the location of messages objects and message catalogs. <img src="../images/opt-end.gif" alt="[Option End]" border=
115 "0"></dd>
116 </dl>
117 </blockquote>
118 <h4 class="mansect"><a name="tag_20_37_09" id="tag_20_37_09"></a>ASYNCHRONOUS EVENTS</h4>
119 <blockquote>
120 <p>Default.</p>
121 </blockquote>
122 <h4 class="mansect"><a name="tag_20_37_10" id="tag_20_37_10"></a>STDOUT</h4>
123 <blockquote>
124 <p>The <i>echo</i> utility arguments shall be separated by single <space> characters and a <newline> character shall
125 follow the last argument. <sup>[<a href="javascript:open_code('XSI')">XSI</a>]</sup> <img src="../images/opt-start.gif" alt=
126 "[Option Start]" border="0"> Output transformations shall occur based on the escape sequences in the input. See the OPERANDS
127 section. <img src="../images/opt-end.gif" alt="[Option End]" border="0"></p>
128 </blockquote>
129 <h4 class="mansect"><a name="tag_20_37_11" id="tag_20_37_11"></a>STDERR</h4>
130 <blockquote>
131 <p>The standard error shall be used only for diagnostic messages.</p>
132 </blockquote>
133 <h4 class="mansect"><a name="tag_20_37_12" id="tag_20_37_12"></a>OUTPUT FILES</h4>
134 <blockquote>
135 <p>None.</p>
136 </blockquote>
137 <h4 class="mansect"><a name="tag_20_37_13" id="tag_20_37_13"></a>EXTENDED DESCRIPTION</h4>
138 <blockquote>
139 <p>None.</p>
140 </blockquote>
141 <h4 class="mansect"><a name="tag_20_37_14" id="tag_20_37_14"></a>EXIT STATUS</h4>
142 <blockquote>
143 <p>The following exit values shall be returned:</p>
144 <dl compact>
145 <dd></dd>
146 <dt> 0</dt>
147 <dd>Successful completion.</dd>
148 <dt>>0</dt>
149 <dd>An error occurred.</dd>
150 </dl>
151 </blockquote>
152 <h4 class="mansect"><a name="tag_20_37_15" id="tag_20_37_15"></a>CONSEQUENCES OF ERRORS</h4>
153 <blockquote>
154 <p>Default.</p>
155 </blockquote>
156 <hr>
157 <div class="box"><em>The following sections are informative.</em></div>
158 <h4 class="mansect"><a name="tag_20_37_16" id="tag_20_37_16"></a>APPLICATION USAGE</h4>
159 <blockquote>
160 <p>It is not possible to use <i>echo</i> portably across all POSIX systems unless escape sequences are omitted, and the first
161 argument does not consist of a <tt>'-'</tt> followed by one or more characters from the set {<tt>'e'</tt>, <tt>'E'</tt>,
162 <tt>'n'</tt>}.</p>
163 <p>The <a href="../utilities/printf.html"><i>printf</i></a> utility can be used portably to emulate any of the traditional
164 behaviors of the <i>echo</i> utility as follows (assuming that <i>IFS</i> has its standard value or is unset):</p>
165 <ul>
166 <li>
167 <p>The historic System V <i>echo</i> and the requirements on XSI implementations in this volume of POSIX.1-2024 are equivalent
168 to:</p>
169 <pre>
170 <tt>printf "%b\n" "$*"
171 </tt></pre></li>
172 <li>
173 <p>The BSD <i>echo</i> is equivalent to:</p>
174 <pre>
175 <tt>if [ "X$1" = "X-n" ]
176 then
177 shift
178 printf "%s" "$*"
179 else
180 printf "%s\n" "$*"
181 fi
182 </tt></pre></li>
183 </ul>
184 <p>New applications are encouraged to use <a href="../utilities/printf.html"><i>printf</i></a> instead of <i>echo</i>.</p>
185 </blockquote>
186 <h4 class="mansect"><a name="tag_20_37_17" id="tag_20_37_17"></a>EXAMPLES</h4>
187 <blockquote>
188 <p>None.</p>
189 </blockquote>
190 <h4 class="mansect"><a name="tag_20_37_18" id="tag_20_37_18"></a>RATIONALE</h4>
191 <blockquote>
192 <p>The <i>echo</i> utility has not been made obsolescent because of its extremely widespread use in historical applications.
193 Conforming applications that wish to do prompting without <newline> characters or that could possibly be expecting to echo a
194 string consisting of a <tt>'-'</tt> followed by one or more characters from the set {<tt>'e'</tt>, <tt>'E'</tt>, <tt>'n'</tt>}
195 should use the <a href="../utilities/printf.html"><i>printf</i></a> utility.</p>
196 <p>At the time that the IEEE Std 1003.2-1992 standard was being developed, the two different historical versions of
197 <i>echo</i> that were considered for standardization varied in incompatible ways.</p>
198 <p>The BSD <i>echo</i> checked the first argument for the string <b>-n</b> which caused it to suppress the <newline> that
199 would otherwise follow the final argument in the output.</p>
200 <p>The System V <i>echo</i> treated all arguments as strings to be written, but allowed escape sequences within them, as described
201 for XSI implementations in the OPERANDS section, including <tt>\c</tt> to suppress a trailing <newline>.</p>
202 <p>Thus the IEEE Std 1003.2-1992 standard said that the behavior was implementation-defined if the first operand is
203 <b>-n</b> or if any of the operands contain a <backslash> character. It also specified that the <i>echo</i> utility does not
204 support Utility Syntax Guideline 10 because historical applications depended on <i>echo</i> to echo <i>all</i> of its arguments,
205 except for the <b>-n</b> first argument in the BSD version.</p>
206 <p>The Single UNIX Specification, Version 1 required the System V behavior, and this became the XSI requirement when Version 2 and
207 POSIX.2 were merged with POSIX.1 to form the joint IEEE Std 1003.1-2001 / Single UNIX Specification, Version 3
208 standard.</p>
209 <p>This standard now treats a first operand of <b>-e</b> or <b>-E</b> the same as <b>-n</b> in recognition that support for them
210 has become more widespread in non-XSI implementations. Where supported, <b>-e</b> enables processing of escape sequences in the
211 remaining operands (in situations where it is disabled by default), and <b>-E</b> disables it (in situations where it is enabled by
212 default). A first operand containing a combination of these three letters, in the same manner as option grouping, also results in
213 implementation-defined behavior.</p>
214 </blockquote>
215 <h4 class="mansect"><a name="tag_20_37_19" id="tag_20_37_19"></a>FUTURE DIRECTIONS</h4>
216 <blockquote>
217 <p>None.</p>
218 </blockquote>
219 <h4 class="mansect"><a name="tag_20_37_20" id="tag_20_37_20"></a>SEE ALSO</h4>
220 <blockquote>
221 <p><a href="../utilities/printf.html#tag_20_96"><i>printf</i></a></p>
222 <p>XBD <a href="../basedefs/V1_chap08.html#tag_08"><i>8. Environment Variables</i></a> , <a href=
223 "../basedefs/V1_chap12.html#tag_12_02"><i>12.2 Utility Syntax Guidelines</i></a></p>
224 </blockquote>
225 <h4 class="mansect"><a name="tag_20_37_21" id="tag_20_37_21"></a>CHANGE HISTORY</h4>
226 <blockquote>
227 <p>First released in Issue 2.</p>
228 </blockquote>
229 <h4 class="mansect"><a name="tag_20_37_22" id="tag_20_37_22"></a>Issue 5</h4>
230 <blockquote>
231 <p>In the OPTIONS section, the last sentence is changed to indicate that implementations "do not" support any options; in the
232 previous issue this said "need not".</p>
233 </blockquote>
234 <h4 class="mansect"><a name="tag_20_37_23" id="tag_20_37_23"></a>Issue 6</h4>
235 <blockquote>
236 <p>The following new requirements on POSIX implementations derive from alignment with the Single UNIX Specification:</p>
237 <ul>
238 <li>
239 <p>A set of character sequences is defined as <i>string</i> operands.</p>
240 </li>
241 <li>
242 <p><i>LC_CTYPE</i> is added to the list of environment variables affecting <i>echo</i>.</p>
243 </li>
244 <li>
245 <p>In the OPTIONS section, implementations shall not support any options.</p>
246 </li>
247 </ul>
248 <p>IEEE Std 1003.1-2001/Cor 1-2002, item XCU/TC1/D6/21 is applied, so that the <i>echo</i> utility can accommodate
249 historical BSD behavior.</p>
250 </blockquote>
251 <h4 class="mansect"><a name="tag_20_37_24" id="tag_20_37_24"></a>Issue 7</h4>
252 <blockquote>
253 <p>SD5-XCU-ERN-97 is applied, updating the SYNOPSIS.</p>
254 </blockquote>
255 <h4 class="mansect"><a name="tag_20_37_25" id="tag_20_37_25"></a>Issue 8</h4>
256 <blockquote>
257 <p>Austin Group Defect 1122 is applied, changing the description of <i>NLSPATH .</i></p>
258 <p>Austin Group Defect 1222 is applied, making the results implementation-defined, on systems that are not XSI-conformant, if the
259 first operand consists of a <tt>'-'</tt> followed by one or more characters from the set {<tt>'e'</tt>, <tt>'E'</tt>,
260 <tt>'n'</tt>}.</p>
261 </blockquote>
262 <div class="box"><em>End of informative text.</em></div>
263 <hr>
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