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12 .TH EXPR 1 "Oct 25, 2017"
13 .SH NAME
14 expr \- evaluate arguments as an expression
15 .SH SYNOPSIS
16 .LP
17 .nf
18 \fB/usr/bin/expr\fR \fIargument\fR...
19 .fi
21 .SH DESCRIPTION
22 .sp
23 .LP
24 The \fBexpr\fR utility evaluates the expression and writes the result to
25 standard output followed by a NEWLINE. If there is no result from \fBexpr\fR
26 processing, a NEWLINE is written to standard output.
27 .SH OPERANDS
28 .sp
29 .LP
30 The \fIargument\fR operand is evaluated as an expression. Terms of the
31 expression must be separated by blanks. Characters special to the shell must be
32 escaped (see \fBsh\fR(1)). Strings containing blanks or other special
33 characters should be quoted. The length of the expression is limited to
34 \fBLINE_MAX\fR (2048 characters).
35 .sp
36 .LP
37 The operators and keywords are listed below. The list is in order of increasing
38 precedence, with equal precedence operators grouped within \fB{\|}\fR symbols.
39 All of the operators are left-associative.
40 .sp
41 .ne 2
42 .na
43 \fB\fIexpr\fR \fB\e|\fR \fIexpr\fR\fR
44 .ad
45 .sp .6
46 .RS 4n
47 Returns the evaluation of the first \fIexpr\fR if it is neither \fINULL\fR nor
48 \fB0\fR; otherwise, returns the evaluation of the second \fIexpr\fR if it is
49 not \fINULL\fR; otherwise, \fB0\fR.
50 .RE
52 .sp
53 .ne 2
54 .na
55 \fB\fIexpr\fR \fB\e&\fR \fIexpr\fR\fR
56 .ad
57 .sp .6
58 .RS 4n
59 Returns the first \fIexpr\fR if neither \fIexpr\fR is \fINULL\fR or \fB0\fR,
60 otherwise returns \fB0\fR.
61 .RE
63 .sp
64 .ne 2
65 .na
66 \fB\fIexpr\fR{ \fB=\fR, \fB\e>\fR, \fB\e>=\fR, \fB\e<\fR, \fB\e<=\fR, \fB!=\fR}
67 \fIexpr\fR\fR
68 .ad
69 .sp .6
70 .RS 4n
71 Returns the result of an integer comparison if both arguments are integers,
72 otherwise returns the result of a string comparison using the locale-specific
73 coalition sequence. The result of each comparison will be \fB1\fR if the
74 specified relationship is \fBTRUE\fR, \fB0\fR if the relationship is
75 \fBFALSE\fR.
76 .RE
78 .sp
79 .ne 2
80 .na
81 \fB\fIexpr \fR{ \fB+\fR, \fB\(mi \fR} \fIexpr\fR\fR
82 .ad
83 .sp .6
84 .RS 4n
85 Addition or subtraction of integer-valued arguments.
86 .RE
88 .sp
89 .ne 2
90 .na
91 \fB\fIexpr \fR{ \fB\e*\fR, \fB/\fR, \fB%\fR} \fIexpr\fR\fR
92 .ad
93 .sp .6
94 .RS 4n
95 Multiplication, division, or remainder of the integer-valued arguments.
96 .RE
98 .sp
99 .ne 2
100 .na
101 \fB\fIexpr\fR \fB:\fR \fIexpr\fR\fR
102 .ad
103 .sp .6
104 .RS 4n
105 The matching operator \fB:\fR (colon) compares the first argument with the
106 second argument, which must be an internationalized basic regular expression
107 (BRE), except that all patterns are anchored to the beginning of the string.
108 That is, only sequences starting at the first character of a string are matched
109 by the regular expression. See \fBregex\fR(5) and NOTES. Normally, the
110 \fBexpr\fR matching operator returns the number of characters
111 matched (\fB0\fR on failure). If the second argument contains at least one BRE
112 sub-expression [\e(...\e)], the matching operator returns the string
113 corresponding to \e1.
114 .RE
116 .sp
117 .ne 2
118 .na
119 \fB\fIinteger\fR \fR
120 .ad
121 .sp .6
122 .RS 4n
123 An argument consisting only of an (optional) unary minus followed by digits.
124 .RE
126 .sp
127 .ne 2
128 .na
129 \fB\fIstring\fR \fR
130 .ad
131 .sp .6
132 .RS 4n
133 A string argument that cannot be identified as an \fIinteger\fR argument or as
134 one of the expression operator symbols.
135 .RE
137 .SS "Compatibility Operators (x86 only)"
138 .sp
139 .LP
140 The following operators are included for compatibility with INTERACTIVE UNIX
141 System only and are not intended to be used by non- INTERACTIVE UNIX System
142 scripts:
143 .sp
144 .ne 2
145 .na
146 \fB\fBindex\fR \fIstring character-list\fR\fR
147 .ad
148 .sp .6
149 .RS 4n
150 Report the first position in which any one of the bytes in \fIcharacter-list\fR
151 matches a byte in \fIstring\fR.
152 .RE
154 .sp
155 .ne 2
156 .na
157 \fB\fBlength\fR \fIstring\fR\fR
158 .ad
159 .sp .6
160 .RS 4n
161 Return the length (that is, the number of bytes) of \fIstring\fR.
162 .RE
164 .sp
165 .ne 2
166 .na
167 \fB\fBsubstr\fR \fIstring integer-1 integer-2\fR\fR
168 .ad
169 .sp .6
170 .RS 4n
171 Extract the substring of \fIstring\fR starting at position \fIinteger-1\fR and
172 of length \fIinteger-2\fR bytes. If \fIinteger-1\fR has a value greater than
173 the number of bytes in \fIstring\fR, \fBexpr\fR returns a null string. If you
174 try to extract more bytes than there are in string, \fBexpr\fR returns all the
175 remaining bytes from \fIstring\fR. Results are unspecified if either
176 \fIinteger-1\fR or \fIinteger-2\fR is a negative value.
177 .RE
179 .SH EXAMPLES
180 .LP
181 \fBExample 1 \fRAdding an integer to a shell variable
182 .sp
183 .LP
184 Add 1 to the shell variable \fBa\fR:
186 .sp
187 .in +2
188 .nf
189 example$ \fBa=`expr\| $a\| +\| 1`\fR
190 .fi
191 .in -2
192 .sp
194 .LP
195 \fBExample 2 \fRReturning a path name segment
196 .sp
197 .LP
198 The following example emulates \fBbasename\fR(1), returning the last segment of
199 the path name \fB$a\fR. For \fB$a\fR equal to either \fB/usr/abc/file\fR or
200 just \fBfile\fR, the example returns \fBfile\fR. (Watch out for \fB/\fR alone
201 as an argument: \fBexpr\fR takes it as the division operator. See NOTES below.)
203 .sp
204 .in +2
205 .nf
206 example$ \fBexpr $a : '.*/\e(.*\e)' \e| $a\fR
207 .fi
208 .in -2
209 .sp
211 .LP
212 \fBExample 3 \fRUsing // characters to simplify the expression
213 .sp
214 .LP
215 Here is a better version of the previous example. The addition of the \fB//\fR
216 characters eliminates any ambiguity about the division operator and simplifies
217 the whole expression.
219 .sp
220 .in +2
221 .nf
222 example$ \fBexpr //$a : '.*/\e(.*\e)'\fR
223 .fi
224 .in -2
225 .sp
227 .LP
228 \fBExample 5 \fRReturning the number of characters in a variable
229 .sp
230 .in +2
231 .nf
232 example$ \fBexpr "$VAR" : '.*'\fR
233 .fi
234 .in -2
235 .sp
237 .SH ENVIRONMENT VARIABLES
238 .sp
239 .LP
240 See \fBenviron\fR(5) for descriptions of the following environment variables
241 that affect the execution of \fBexpr\fR: \fBLANG\fR, \fBLC_ALL\fR,
242 \fBLC_COLLATE\fR, \fBLC_CTYPE\fR, \fBLC_MESSAGES\fR, and \fBNLSPATH\fR.
243 .SH EXIT STATUS
244 .sp
245 .LP
246 As a side effect of expression evaluation, \fBexpr\fR returns the following
247 exit values:
248 .sp
249 .ne 2
250 .na
251 \fB\fB0\fR \fR
252 .ad
253 .RS 7n
254 If the expression is neither \fINULL\fR nor \fB0\fR.
255 .RE
257 .sp
258 .ne 2
259 .na
260 \fB\fB1\fR \fR
261 .ad
262 .RS 7n
263 If the expression is either \fINULL\fR or \fB0\fR.
264 .RE
266 .sp
267 .ne 2
268 .na
269 \fB\fB2\fR \fR
270 .ad
271 .RS 7n
272 For invalid expressions.
273 .RE
275 .sp
276 .ne 2
277 .na
278 \fB\fB>2\fR \fR
279 .ad
280 .RS 7n
281 An error occurred.
282 .RE
284 .SH ATTRIBUTES
285 .sp
286 .LP
287 See \fBattributes\fR(5) for descriptions of the following attributes:
288 .sp
290 .sp
291 .TS
292 box;
293 c | c
294 l | l .
295 ATTRIBUTE TYPE ATTRIBUTE VALUE
296 _
297 CSI enabled
298 _
299 Interface Stability Standard
300 .TE
302 .SH SEE ALSO
303 .sp
304 .LP
305 \fBbasename\fR(1), \fBed\fR(1), \fBsh\fR(1), \fBIntro\fR(3),
306 \fBattributes\fR(5), \fBenviron\fR(5), \fBregex\fR(5), \fBstandards\fR(5)
307 .SH DIAGNOSTICS
308 .sp
309 .ne 2
310 .na
311 \fB\fBsyntax error\fR\fR
312 .ad
313 .RS 24n
314 Operator and operand errors.
315 .RE
317 .sp
318 .ne 2
319 .na
320 \fB\fBnon-numeric argument\fR\fR
321 .ad
322 .RS 24n
323 Arithmetic is attempted on such a string.
324 .RE
326 .SH NOTES
327 .sp
328 .LP
329 After argument processing by the shell, \fBexpr\fR cannot tell the difference
330 between an operator and an operand except by the value. If \fB$a\fR is an
331 \fB=\fR, the command:
332 .sp
333 .in +2
334 .nf
335 example$ \fBexpr $a = '='\fR
336 .fi
337 .in -2
338 .sp
340 .sp
341 .LP
342 looks like:
343 .sp
344 .in +2
345 .nf
346 example$ \fBexpr = = =\fR
347 .fi
348 .in -2
349 .sp
351 .sp
352 .LP
353 as the arguments are passed to \fBexpr\fR (and they are all taken as the
354 \fB=\fR operator). The following works:
355 .sp
356 .in +2
357 .nf
358 example$ \fBexpr X$a = X=\fR
359 .fi
360 .in -2
361 .sp
363 .SS "Regular Expressions"
364 .sp
365 .LP
366 Unlike some previous versions, \fBexpr\fR uses Internationalized Basic Regular
367 Expressions for all system-provided locales. Internationalized Regular
368 Expressions are explained on the \fBregex\fR(5) manual page.