1expr(1B) SunOS/BSD Compatibility Package Commands expr(1B)
2
6 expr - evaluate arguments as a logical, arithmetic, or string expres‐
7 sion
8
10 /usr/ucb/expr argument...
11
14 The expr utility evaluates expressions as specified by its arguments.
15 After evaluation, the result is written on the standard output. Each
16 token of the expression is a separate argument, so terms of the expres‐
17 sion must be separated by blanks. Characters special to the shell must
18 be escaped. Note: 0 is returned to indicate a zero value, rather than
19 the null string. Strings containing blanks or other special characters
20 should be quoted. Integer-valued arguments may be preceded by a unary
21 minus sign. Internally, integers are treated as 32-bit, two's-comple‐
22 ment numbers.
23 The operators and keywords are listed below. Characters that need to be
26 escaped are preceded by `\'. The list is in order of increasing prece‐
27 dence, with equal precedence operators grouped within {} symbols.
28 expr \| expr
30 Returns the evaluation of the first expr if it is neither NULL nor
32 0; otherwise, returns the evaluation of the second expr if it is
33 not NULL; otherwise, 0.
34 expr \& expr
37 Returns the first expr if neither expr is NULL or 0, otherwise
39 returns 0.
40 expr { =, \, \ , \<, \<=, != } expr
43 Returns the result of an integer comparison if both arguments are
45 integers, otherwise returns the result of a lexical comparison.
46 expr { +, − } expr
49 Addition or subtraction of integer-valued arguments.
51 expr { \, /, % } expr
54 Multiplication, division, or remainder of the integer-valued argu‐
56 ments.
57 string : regular-expression
60 match string regular-expression
61 The two forms of the matching operator above are synonymous. The
63 matching operators : and match compare the first argument with the
64 second argument which must be a regular expression. Regular expres‐
65 sion syntax is the same as that of regexp(5), except that all pat‐
66 terns are "anchored" (treated as if they begin with ^) and there‐
67 fore ^ is not a special character, in that context. Normally, the
68 matching operator returns the number of characters matched (0 on
69 failure). Alternatively, the \...\ pattern symbols can be used to
70 return a portion of the first argument.
71 substr string integer-1 integer-2
74 Extracts the substring of string starting at position integer-1
76 and of length integer-2 characters. If integer-1 has a value
77 greater than the length of string, expr returns a null string. If
78 you try to extract more characters than there are in string, expr
79 returns all the remaining characters from string. Beware of using
80 negative values for either integer-1 or integer-2 as expr tends to
81 run forever in these cases.
82 index string character-list
85 Reports the first position in string at which any one of the char‐
87 acters in character-list matches a character in string.
88 length string
91 Returns the length (that is, the number of characters) of string.
93 ( expr )
96 Parentheses may be used for grouping.
98
101 Example 1 Adding an integer to a shell variable
102 Add 1 to the shell variable a.
105 a='expr $a + 1'
108 Example 2 Returning a path name segment
112 Return the last segment of a path name (that is, the filename part).
115 Watch out for / alone as an argument: expr will take it as the division
116 operator (see BUGS below).
117 # 'For $a equal to either "/usr/abc/file" or just "file"'
120 expr $a : '.*/\ \ $a
121 Example 3 Using // characters to simplify the expression
125 The addition of the // characters eliminates any ambiguity about the
128 division operator and simplifies the whole expression.
129 # A better representation of example 2.
132 expr //$a : '.*/\
133 Example 4 Returning the value of a variable
137 Returns the number of characters in $VAR.
140 expr $VAR : '.*'
143
147 expr returns the following exit codes:
148 0 If the expression is neither NULL nor 0.
150 1 If the expression is NULL or 0.
153 2 For invalid expressions.
156
159 See attributes(5) for descriptions of the following attributes:
160 ┌─────────────────────────────┬─────────────────────────────┐
165 │ ATTRIBUTE TYPE │ ATTRIBUTE VALUE │
166 ├─────────────────────────────┼─────────────────────────────┤
167 │Availability │SUNWscpu │
168 └─────────────────────────────┴─────────────────────────────┘
169
171 sh(1), test(1), attributes(5), regexp(5)
172
174 syntax error for operator/operand errors
175 non-numeric argument if arithmetic is attempted on such a string
178 division by zero if an attempt to divide by zero is made
181
184 After argument processing by the shell, expr cannot tell the difference
185 between an operator and an operand except by the value. If $a is an =,
186 the command:
187 expr $a = '='
189 looks like:
194 expr = = =
196 as the arguments are passed to expr (and they will all be taken as the
201 = operator). The following works:
202 expr X$a = X=
204 Note: the match, substr, length, and index operators cannot themselves
209 be used as ordinary strings. That is, the expression:
210 example% expr index expurgatorious length
212 syntax error
213 example%
214 generates the `syntax error' message as shown instead of the value 1 as
219 you might expect.
220SunOS 5.11 6 Jun 2000 expr(1B)