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38 .Nd evaluate expression
48 and writes the result on standard output.
50 All operators and operands must be passed as separate arguments.
51 Several of the operators have special meaning to command interpreters
52 and must therefore be quoted appropriately.
53 All integer operands are interpreted in base 10.
55 Arithmetic operations are performed using signed integer math.
58 flag is specified, arithmetic uses the C
60 data type (the largest integral type available), and
62 will detect arithmetic overflow and return an error indication.
63 If a numeric operand is specified which is so large as to overflow
64 conversion to an integer, it is parsed as a string instead.
67 is not specified, arithmetic operations and parsing of integer
68 arguments will overflow silently according to the rules of the C
73 Operators are listed below in order of increasing precedence; all
75 Operators with equal precedence are grouped within { } symbols.
76 .Bl -tag -width indent
77 .It Ar expr1 Li | Ar expr2
78 Return the evaluation of
80 if it is neither an empty string nor zero;
81 otherwise, returns the evaluation of
83 .It Ar expr1 Li & Ar expr2
84 Return the evaluation of
86 if neither expression evaluates to an empty string or zero;
87 otherwise, returns zero.
88 .It Ar expr1 Li "{=, >, >=, <, <=, !=}" Ar expr2
89 Return the results of integer comparison if both arguments are integers;
90 otherwise, returns the results of string comparison using the locale-specific
92 The result of each comparison is 1 if the specified relation is true,
93 or 0 if the relation is false.
94 .It Ar expr1 Li "{+, -}" Ar expr2
95 Return the results of addition or subtraction of integer-valued arguments.
96 .It Ar expr1 Li "{*, /, %}" Ar expr2
97 Return the results of multiplication, integer division, or remainder of integer-valued arguments.
98 .It Ar expr1 Li : Ar expr2
105 which must be a basic regular expression.
106 The regular expression is anchored
107 to the beginning of the string with an implicit
110 If the match succeeds and the pattern contains at least one regular
111 expression subexpression
113 the string corresponding to
116 otherwise the matching operator returns the number of characters matched.
117 If the match fails and the pattern contains a regular expression subexpression
118 the null string is returned;
122 Parentheses are used for grouping in the usual manner.
126 utility makes no lexical distinction between arguments which may be
127 operators and arguments which may be operands.
128 An operand which is lexically identical to an operator will be considered a
130 See the examples below for a work-around.
134 command in general is historic and inconvenient.
135 New applications are advised to use shell arithmetic rather than
137 .Ss Compatibility with previous implementations
141 compatibility is enabled, this version of
145 Utility Syntax Guidelines, which require that a leading argument beginning
146 with a minus sign be considered an option to the program.
149 syntax may be used to prevent this interpretation.
150 However, many historic implementations of
152 including the one in previous versions of
154 will not permit this syntax.
155 See the examples below for portable ways to guarantee the correct
158 .Xr check_utility_compat 3
163 is used to determine whether compatibility mode should be enabled.
164 This feature is intended for use as a transition and debugging aid, when
166 is used in complex scripts which cannot easily be recast to avoid the
168 Enabling compatibility mode
169 also implicitly enables the
171 option, since this matches the historic behavior of
175 For historical reasons, defining the environment variable
177 also enables compatibility mode.
179 .Bl -tag -width ".Ev EXPR_COMPAT"
181 If set, enables compatibility mode.
186 utility exits with one of the following values:
187 .Bl -tag -width indent -compact
189 the expression is neither an empty string nor 0.
191 the expression is an empty string or 0.
193 the expression is invalid.
198 The following example (in
200 syntax) adds one to the variable
202 .Dl "a=$(expr $a + 1)"
204 This will fail if the value of
206 is a negative number.
207 To protect negative values of
209 from being interpreted as options to the
211 command, one might rearrange the expression:
212 .Dl "a=$(expr 1 + $a)"
214 More generally, parenthesize possibly-negative values:
215 .Dl "a=$(expr \e( $a \e) + 1)"
217 This example prints the filename portion of a pathname stored
222 might represent the path
224 it is necessary to prevent it from being interpreted as the division operator.
227 characters resolve this ambiguity.
228 .Dl "expr \*q//$a\*q \&: '.*/\e(.*\e)'"
231 The following examples output the number of characters in variable
235 might begin with a hyphen, it is necessary to prevent it from being
236 interpreted as an option to
245 .Dl "expr -- \*q$a\*q \&: \*q.*\*q"
247 For portability to older systems, however, a more complicated command
249 .Dl "expr \e( \*qX$a\*q \&: \*q.*\*q \e) - 1"
254 .Xr check_utility_compat 3
260 provided that compatibility mode is not enabled.
263 flag is an extension.