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23 <script language="JavaScript" src="../jscript/codes.js"></script><basefont size="3">
24 <center><font size="2">The Open Group Base Specifications Issue 8<br>
25 IEEE Std 1003.1-2024<br>
26 Copyright © 2001-2024 The IEEE and The Open Group</font></center>
27 <hr size="2" noshade>
28 <a name="top" id="top"></a> <a name="expr" id="expr"></a> <a name="tag_20_42" id="tag_20_42"></a><!-- expr -->
29 <h4 class="mansect"><a name="tag_20_42_01" id="tag_20_42_01"></a>NAME</h4>
30 <blockquote>expr — evaluate arguments as an expression</blockquote>
31 <h4 class="mansect"><a name="tag_20_42_02" id="tag_20_42_02"></a>SYNOPSIS</h4>
32 <blockquote class="synopsis">
33 <p><code><tt>expr</tt> <i>operand</i><tt>...</tt></code></p>
34 </blockquote>
35 <h4 class="mansect"><a name="tag_20_42_03" id="tag_20_42_03"></a>DESCRIPTION</h4>
36 <blockquote>
37 <p>The <i>expr</i> utility shall evaluate an expression and write the result to standard output.</p>
38 </blockquote>
39 <h4 class="mansect"><a name="tag_20_42_04" id="tag_20_42_04"></a>OPTIONS</h4>
40 <blockquote>
41 <p>None.</p>
42 </blockquote>
43 <h4 class="mansect"><a name="tag_20_42_05" id="tag_20_42_05"></a>OPERANDS</h4>
44 <blockquote>
45 <p>The single expression evaluated by <i>expr</i> shall be formed from the <i>operand</i> operands, as described in the EXTENDED
46 DESCRIPTION section. The application shall ensure that each of the expression operator symbols:</p>
47 <pre>
48 <tt>( ) | & = > >= < <= != + - * / % :
49 </tt></pre>
50 <p>and the symbols <i>integer</i> and <i>string</i> in the table are provided as separate arguments to <i>expr</i>.</p>
51 </blockquote>
52 <h4 class="mansect"><a name="tag_20_42_06" id="tag_20_42_06"></a>STDIN</h4>
53 <blockquote>
54 <p>Not used.</p>
55 </blockquote>
56 <h4 class="mansect"><a name="tag_20_42_07" id="tag_20_42_07"></a>INPUT FILES</h4>
57 <blockquote>
58 <p>None.</p>
59 </blockquote>
60 <h4 class="mansect"><a name="tag_20_42_08" id="tag_20_42_08"></a>ENVIRONMENT VARIABLES</h4>
61 <blockquote>
62 <p>The following environment variables shall affect the execution of <i>expr</i>:</p>
63 <dl compact>
64 <dd></dd>
65 <dt><i>LANG</i></dt>
66 <dd>Provide a default value for the internationalization variables that are unset or null. (See XBD <a href=
67 "../basedefs/V1_chap08.html#tag_08_02"><i>8.2 Internationalization Variables</i></a> for the precedence of internationalization
68 variables used to determine the values of locale categories.)</dd>
69 <dt><i>LC_ALL</i></dt>
70 <dd>If set to a non-empty string value, override the values of all the other internationalization variables.</dd>
71 <dt><i>LC_COLLATE</i></dt>
72 <dd><br>
73 Determine the locale for the behavior of ranges, equivalence classes, and multi-character collating elements within regular
74 expressions and by the string comparison operators.</dd>
75 <dt><i>LC_CTYPE</i></dt>
76 <dd>Determine the locale for the interpretation of sequences of bytes of text data as characters (for example, single-byte as
77 opposed to multi-byte characters in arguments) and the behavior of character classes within regular expressions.</dd>
78 <dt><i>LC_MESSAGES</i></dt>
79 <dd><br>
80 Determine the locale that should be used to affect the format and contents of diagnostic messages written to standard error.</dd>
81 <dt><i>NLSPATH</i></dt>
82 <dd><sup>[<a href="javascript:open_code('XSI')">XSI</a>]</sup> <img src="../images/opt-start.gif" alt="[Option Start]" border="0">
83 Determine the location of messages objects and message catalogs. <img src="../images/opt-end.gif" alt="[Option End]" border=
84 "0"></dd>
85 </dl>
86 </blockquote>
87 <h4 class="mansect"><a name="tag_20_42_09" id="tag_20_42_09"></a>ASYNCHRONOUS EVENTS</h4>
88 <blockquote>
89 <p>Default.</p>
90 </blockquote>
91 <h4 class="mansect"><a name="tag_20_42_10" id="tag_20_42_10"></a>STDOUT</h4>
92 <blockquote>
93 <p>The <i>expr</i> utility shall evaluate the expression and write the result, followed by a <newline>, to standard
94 output.</p>
95 </blockquote>
96 <h4 class="mansect"><a name="tag_20_42_11" id="tag_20_42_11"></a>STDERR</h4>
97 <blockquote>
98 <p>The standard error shall be used only for diagnostic messages.</p>
99 </blockquote>
100 <h4 class="mansect"><a name="tag_20_42_12" id="tag_20_42_12"></a>OUTPUT FILES</h4>
101 <blockquote>
102 <p>None.</p>
103 </blockquote>
104 <h4 class="mansect"><a name="tag_20_42_13" id="tag_20_42_13"></a>EXTENDED DESCRIPTION</h4>
105 <blockquote>
106 <p>The formation of the expression to be evaluated is shown in the following table. The symbols <i>expr</i>, <i>expr1</i>, and
107 <i>expr2</i> represent expressions formed from <i>integer</i> and <i>string</i> symbols and the expression operator symbols (all
108 separate arguments) by recursive application of the constructs described in the table. The expressions are listed in order of
109 decreasing precedence, with equal-precedence operators grouped between horizontal lines. All of the operators shall be
110 left-associative.</p>
111 <center>
112 <table border="1" cellpadding="3" align="center">
113 <tr valign="top">
114 <th align="center">
115 <p class="tent"><b>Expression</b></p>
116 </th>
117 <th align="center">
118 <p class="tent"><b>Description</b></p>
119 </th>
120 </tr>
121 <tr valign="top">
122 <td align="left">
123 <p class="tent"><i>integer</i></p>
124 </td>
125 <td align="left">
126 <p class="tent">An argument consisting only of an (optional) unary minus followed by digits.</p>
127 </td>
128 </tr>
129 <tr valign="top">
130 <td align="left">
131 <p class="tent"><i>string</i></p>
132 </td>
133 <td align="left">
134 <p class="tent">A string argument; see below.</p>
135 </td>
136 </tr>
137 <tr valign="top">
138 <td align="left">
139 <p class="tent">( <i>expr</i> )</p>
140 </td>
141 <td align="left">
142 <p class="tent">Grouping symbols. Any expression can be placed within parentheses. Parentheses can be nested to a depth of
143 {EXPR_NEST_MAX}.</p>
144 </td>
145 </tr>
146 <tr valign="top">
147 <td align="left">
148 <p class="tent"><i>expr1</i> : <i>expr2</i></p>
149 </td>
150 <td align="left">
151 <p class="tent">Matching expression; see below.</p>
152 </td>
153 </tr>
154 <tr valign="top">
155 <td align="left">
156 <p class="tent"><br>
157 <i>expr1</i> * <i>expr2</i><br>
158 <br>
159 <i>expr1</i> / <i>expr2</i><br>
160 <br>
161 <i>expr1</i> % <i>expr2</i><br></p>
162 </td>
163 <td align="left">
164 <p class="tent"><br>
165 Multiplication of decimal integer-valued arguments.<br>
166 <br>
167 Integer division of decimal integer-valued arguments, producing an integer result.<br>
168 <br>
169 Remainder of integer division of decimal integer-valued arguments.<br></p>
170 </td>
171 </tr>
172 <tr valign="top">
173 <td align="left">
174 <p class="tent"><br>
175 <i>expr1</i> + <i>expr2</i><br>
176 <br>
177 <i>expr1</i> - <i>expr2</i><br></p>
178 </td>
179 <td align="left">
180 <p class="tent"><br>
181 Addition of decimal integer-valued arguments.<br>
182 <br>
183 Subtraction of decimal integer-valued arguments.<br></p>
184 </td>
185 </tr>
186 <tr valign="top">
187 <td align="left">
188 <p class="tent"><br>
189 <br>
190 <br>
191 <br>
192 <br>
193 <i>expr1</i> = <i>expr2</i><br>
194 <i>expr1</i> > <i>expr2</i><br>
195 <i>expr1</i> >= <i>expr2</i><br>
196 <i>expr1</i> < <i>expr2</i><br>
197 <i>expr1</i> <= <i>expr2</i><br>
198 <i>expr1</i> != <i>expr2</i><br></p>
199 </td>
200 <td align="left">
201 <p class="tent"><br>
202 Returns the result of a decimal integer comparison if both arguments are integers; otherwise, returns the result of a string
203 comparison using the locale-specific collation sequence. The result of each<br>
204 comparison is 1 if the specified relationship is true, or 0 if the relationship is false.<br>
205 <br>
206 Equal.<br>
207 Greater than.<br>
208 Greater than or equal.<br>
209 Less than.<br>
210 Less than or equal.<br>
211 Not equal.<br></p>
212 </td>
213 </tr>
214 <tr valign="top">
215 <td align="left">
216 <p class="tent"><i>expr1</i> & <i>expr2</i></p>
217 </td>
218 <td align="left">
219 <p class="tent">Returns the evaluation of <i>expr1</i> if neither expression evaluates to null or zero; otherwise, returns
220 zero.</p>
221 </td>
222 </tr>
223 <tr valign="top">
224 <td align="left">
225 <p class="tent"><i>expr1</i> | <i>expr2</i></p>
226 </td>
227 <td align="left">
228 <p class="tent">Returns the evaluation of <i>expr1</i> if it is neither null nor zero; otherwise, returns the evaluation of
229 <i>expr2</i> if it is not null; otherwise, zero.</p>
230 </td>
231 </tr>
232 </table>
233 </center>
234 <h5><a name="tag_20_42_13_01" id="tag_20_42_13_01"></a>Matching Expression</h5>
235 <p class="tent">The <tt>':'</tt> matching operator shall compare the string resulting from the evaluation of <i>expr1</i> with the
236 regular expression pattern resulting from the evaluation of <i>expr2</i>. Regular expression syntax shall be that defined in XBD
237 <a href="../basedefs/V1_chap09.html#tag_09_03"><i>9.3 Basic Regular Expressions</i></a> , except that all patterns are anchored to
238 the beginning of the string (that is, only sequences starting at the first character of a string are matched by the regular
239 expression) and, therefore, it is unspecified whether <tt>'^'</tt> is a special character in that context. Usually, the matching
240 operator shall return a string representing the number of characters matched (<tt>'0'</tt> on failure). Alternatively, if the
241 pattern contains at least one regular expression subexpression <tt>"\(...\)"</tt>, the string matched by the back-reference
242 expression <tt>"\1"</tt> shall be returned. If the back-reference expression <tt>"\1"</tt> does not match, then the null string
243 shall be returned.</p>
244 <h5><a name="tag_20_42_13_02" id="tag_20_42_13_02"></a>Identification as Integer or String</h5>
245 <p class="tent">An argument or the value of a subexpression that consists only of an optional unary minus followed by digits is a
246 candidate for treatment as an integer if it is used as the left argument to the <tt>|</tt> operator or as either argument to any of
247 the following operators: <tt>& = > >= < <= != + - * / %</tt>. Otherwise, the argument or subexpression value shall be
248 treated as a string.</p>
249 <p class="tent">The use of string arguments <b>length</b>, <b>substr</b>, <b>index</b>, or <b>match</b> produces unspecified
250 results.</p>
251 </blockquote>
252 <h4 class="mansect"><a name="tag_20_42_14" id="tag_20_42_14"></a>EXIT STATUS</h4>
253 <blockquote>
254 <p>The following exit values shall be returned:</p>
255 <dl compact>
256 <dd></dd>
257 <dt> 0</dt>
258 <dd>The <i>expression</i> evaluated to neither null nor zero, and the output specified in STDOUT was successfully written to
259 standard output.</dd>
260 <dt> 1</dt>
261 <dd>The <i>expression</i> evaluated to null or zero, and the output specified in STDOUT was successfully written to standard
262 output.</dd>
263 <dt> 2</dt>
264 <dd>Invalid <i>expression</i> error.</dd>
265 <dt>>2</dt>
266 <dd>Another error occurred.</dd>
267 </dl>
268 </blockquote>
269 <h4 class="mansect"><a name="tag_20_42_15" id="tag_20_42_15"></a>CONSEQUENCES OF ERRORS</h4>
270 <blockquote>
271 <p>Default.</p>
272 </blockquote>
273 <hr>
274 <div class="box"><em>The following sections are informative.</em></div>
275 <h4 class="mansect"><a name="tag_20_42_16" id="tag_20_42_16"></a>APPLICATION USAGE</h4>
276 <blockquote>
277 <p>The <i>expr</i> utility has a rather difficult syntax:</p>
278 <ul>
279 <li class="tent">Many of the operators are also shell control operators or reserved words, so they have to be escaped on the
280 command line.</li>
281 <li class="tent">Each part of the expression is composed of separate arguments, so liberal usage of <blank> characters is
282 required. For example:
283 <center>
284 <table border="1" cellpadding="3" align="center">
285 <tr valign="top">
286 <th align="center">
287 <p class="tent"><b>Invalid</b></p>
288 </th>
289 <th align="center">
290 <p class="tent"><b>Valid</b></p>
291 </th>
292 </tr>
293 <tr valign="top">
294 <td align="left">
295 <p class="tent"><i>expr</i> <tt>1+2</tt></p>
296 </td>
297 <td align="left">
298 <p class="tent"><i>expr</i> <tt>1 + 2</tt></p>
299 </td>
300 </tr>
301 <tr valign="top">
302 <td align="left">
303 <p class="tent"><i>expr</i> <tt>"1 + 2"</tt></p>
304 </td>
305 <td align="left">
306 <p class="tent"><i>expr</i> <tt>1 + 2</tt></p>
307 </td>
308 </tr>
309 <tr valign="top">
310 <td align="left">
311 <p class="tent"><i>expr</i> <tt>1 + (2 * 3)</tt></p>
312 </td>
313 <td align="left">
314 <p class="tent"><i>expr</i> <tt>1 + \( 2 \* 3 \)</tt></p>
315 </td>
316 </tr>
317 </table>
318 </center>
319 </li>
320 </ul>
321 <p class="tent">In many cases, the arithmetic and string features provided as part of the shell command language are easier to use
322 than their equivalents in <i>expr</i>. Newly written scripts should avoid <i>expr</i> in favor of the new features within the
323 shell; see <a href="../utilities/V3_chap02.html#tag_19_05"><i>2.5 Parameters and Variables</i></a> and <a href=
324 "../utilities/V3_chap02.html#tag_19_06_04"><i>2.6.4 Arithmetic Expansion</i></a> .</p>
325 <p class="tent">After argument processing by the shell, <i>expr</i> is not required to be able to tell the difference between an
326 operator and an operand except by the value. If <tt>"$a"</tt> is <tt>'='</tt>, the command:</p>
327 <pre>
328 <tt>expr "$a" = '='
329 </tt></pre>
330 <p class="tent">looks like:</p>
331 <pre>
332 <tt>expr = = =
333 </tt></pre>
334 <p class="tent">as the arguments are passed to <i>expr</i> (and they all may be taken as the <tt>'='</tt> operator). The following
335 works reliably:</p>
336 <pre>
337 <tt>expr "X$a" = X=
338 </tt></pre>
339 <p class="tent">Also note that this volume of POSIX.1-2024 permits implementations to extend utilities. The <i>expr</i> utility
340 permits the integer arguments to be preceded with a unary minus. This means that an integer argument could look like an option.
341 Therefore, the conforming application must employ the <tt>"--"</tt> construct of Guideline 10 of XBD <a href=
342 "../basedefs/V1_chap12.html#tag_12_02"><i>12.2 Utility Syntax Guidelines</i></a> to protect its operands if there is any chance the
343 first operand might be a negative integer (or any string with a leading minus).</p>
344 <p class="tent">For testing string equality the <a href="../utilities/test.html"><i>test</i></a> utility is preferred over
345 <i>expr</i>, as it is usually implemented as a shell built-in. However, the functionality is not quite the same because the
346 <i>expr</i> <tt>=</tt> and <tt>!=</tt> operators check whether strings collate equally, whereas <a href=
347 "../utilities/test.html"><i>test</i></a> checks whether they are identical. Therefore, they can produce different results in
348 locales where the collation sequence does not have a total ordering of all characters (see XBD <a href=
349 "../basedefs/V1_chap07.html#tag_07_03_02"><i>7.3.2 LC_COLLATE</i></a> ).<br></p>
350 </blockquote>
351 <h4 class="mansect"><a name="tag_20_42_17" id="tag_20_42_17"></a>EXAMPLES</h4>
352 <blockquote>
353 <p>The following command:</p>
354 <pre>
355 <tt>a=$(expr "$a" + 1)
356 </tt></pre>
357 <p class="tent">adds 1 to the variable <i>a</i>.</p>
358 <p class="tent">The following command, for <tt>"$a"</tt> equal to either <b>/usr/abc/file</b> or just <b>file</b>:</p>
359 <pre>
360 <tt>expr $a : '.*/\(.*\)' \| $a
361 </tt></pre>
362 <p class="tent">returns the last segment of a pathname (that is, <b>file</b>). Applications should avoid the character <tt>'/'</tt>
363 used alone as an argument; <i>expr</i> may interpret it as the division operator.</p>
364 <p class="tent">The following command:</p>
365 <pre>
366 <tt>expr "//$a" : '.*/\(.*\)'
367 </tt></pre>
368 <p class="tent">is a better representation of the previous example. The addition of the <tt>"//"</tt> characters eliminates any
369 ambiguity about the division operator and simplifies the whole expression. Also note that pathnames may contain characters
370 contained in the <i>IFS</i> variable and should be quoted to avoid having <tt>"$a"</tt> expand into multiple arguments.</p>
371 <p class="tent">The following command:</p>
372 <pre>
373 <tt>expr "X$VAR" : '.*' - 1
374 </tt></pre>
375 <p class="tent">returns the number of characters in <i>VAR</i>.</p>
376 </blockquote>
377 <h4 class="mansect"><a name="tag_20_42_18" id="tag_20_42_18"></a>RATIONALE</h4>
378 <blockquote>
379 <p>In an early proposal, EREs were used in the matching expression syntax. This was changed to BREs to avoid breaking historical
380 applications.</p>
381 <p class="tent">The use of a leading <circumflex> in the BRE is unspecified because many historical implementations have
382 treated it as a special character, despite their system documentation. For example:</p>
383 <pre>
384 <tt>expr foo : ^foo expr ^foo : ^foo
385 </tt></pre>
386 <p class="tent">return 3 and 0, respectively, on those systems; their documentation would imply the reverse. Thus, the anchoring
387 condition is left unspecified to avoid breaking historical scripts relying on this undocumented feature.</p>
388 </blockquote>
389 <h4 class="mansect"><a name="tag_20_42_19" id="tag_20_42_19"></a>FUTURE DIRECTIONS</h4>
390 <blockquote>
391 <p>None.</p>
392 </blockquote>
393 <h4 class="mansect"><a name="tag_20_42_20" id="tag_20_42_20"></a>SEE ALSO</h4>
394 <blockquote>
395 <p><a href="../utilities/V3_chap02.html#tag_19_05"><i>2.5 Parameters and Variables</i></a> , <a href=
396 "../utilities/V3_chap02.html#tag_19_06_04"><i>2.6.4 Arithmetic Expansion</i></a></p>
397 <p class="tent">XBD <a href="../basedefs/V1_chap07.html#tag_07_03_02"><i>7.3.2 LC_COLLATE</i></a> , <a href=
398 "../basedefs/V1_chap08.html#tag_08"><i>8. Environment Variables</i></a> , <a href="../basedefs/V1_chap09.html#tag_09_03"><i>9.3
399 Basic Regular Expressions</i></a> , <a href="../basedefs/V1_chap12.html#tag_12_02"><i>12.2 Utility Syntax Guidelines</i></a></p>
400 </blockquote>
401 <h4 class="mansect"><a name="tag_20_42_21" id="tag_20_42_21"></a>CHANGE HISTORY</h4>
402 <blockquote>
403 <p>First released in Issue 2.</p>
404 </blockquote>
405 <h4 class="mansect"><a name="tag_20_42_22" id="tag_20_42_22"></a>Issue 5</h4>
406 <blockquote>
407 <p>The FUTURE DIRECTIONS section is added.</p>
408 </blockquote>
409 <h4 class="mansect"><a name="tag_20_42_23" id="tag_20_42_23"></a>Issue 6</h4>
410 <blockquote>
411 <p>The <i>expr</i> utility is aligned with the IEEE P1003.2b draft standard, to include resolution of IEEE PASC Interpretation
412 1003.2 #104.</p>
413 <p class="tent">The normative text is reworded to avoid use of the term "must" for application requirements.</p>
414 </blockquote>
415 <h4 class="mansect"><a name="tag_20_42_24" id="tag_20_42_24"></a>Issue 7</h4>
416 <blockquote>
417 <p>Austin Group Interpretation 1003.1-2001 #036 is applied, clarifying the behavior for BREs.</p>
418 <p class="tent">The SYNOPSIS and OPERANDS sections are revised to explicitly state that the name of each of the operands is
419 <i>operand</i>.</p>
420 <p class="tent">POSIX.1-2008, Technical Corrigendum 2, XCU/TC2-2008/0094 [942], XCU/TC2-2008/0095 [709], XCU/TC2-2008/0096 [942],
421 XCU/TC2-2008/0097 [963], and XCU/TC2-2008/0098 [942] are applied.</p>
422 </blockquote>
423 <h4 class="mansect"><a name="tag_20_42_25" id="tag_20_42_25"></a>Issue 8</h4>
424 <blockquote>
425 <p>Austin Group Defect 1122 is applied, changing the description of <i>NLSPATH .</i></p>
426 <p class="tent">Austin Group Defect 1500 is applied, changing the EXIT STATUS section.</p>
427 <p class="tent">Austin Group Defect 1757 is applied, changing <tt>"[\(...\)]"</tt> to <tt>"\(...\)"</tt>.</p>
428 </blockquote>
429 <div class="box"><em>End of informative text.</em></div>
430 <hr>
431 <p> </p>
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