expr(1)

expr -- evaluate arguments as an expression

Synopsis

expr arguments

Description

The arguments are taken as an expression. After evaluation, the result is written on the standard output. Terms of the expression must be separated by blanks. Characters special to the shell must be escaped. Note that 0 is returned to indicate a zero value, rather than the null string. Strings containing blanks or other special characters should be quoted. Integer-valued arguments may be preceded by a unary minus sign. Internally, integers are treated as 32-bit, 2s complement numbers. The length of the expression is limited to 512 characters. Expressions may be grouped using (escaped) parentheses.

The operators and keywords are listed below. Characters that need to be escaped in the shell (see sh(1)) are preceded by ``\''. The list is in order of increasing precedence, with equal precedence operators grouped within {} symbols.

expr \| expr: Return the first expr if it is neither null nor 0, otherwise return the second expr.
expr \& expr: Return the first expr if neither expr is null or 0, otherwise return 0.
expr { =, \>, \>=, \<, \<=, != } expr: Return the result of an integer comparison if both arguments are integers, otherwise return the result of a lexical comparison.
expr { +, - } expr: Add or subtract integer-valued arguments.
expr { \*, /, % } expr: Multiply, divide, or compute remainder of integer-valued arguments.
expr : expr
match expr expr: Compare the first argument with the second argument, which must be a regular expression. Regular expression syntax is the same as that of ed(1), except that all patterns are ``anchored'' (that is, begin with ``^'') and, therefore, ``^'' is not a special character, in that context. Normally, the matching operator returns the number of characters matched (0 on failure). Alternatively, the $ . . . $ pattern symbols can be used to return a portion of the first argument.
length string: Return the length of string.
substr string index count: Return the portion of string composed of at most count characters starting at the character position of string as expressed by index (where the first character of string is index 1, not 0).
index string character_sequence: Return the index of the first character in string that is also in character_sequence or 0 to indicate no match.

expr processes supplementary code set characters according to the locale specified in the LC_CTYPE environment variable (see LANG on environ(5)). In regular expressions, pattern searches are performed on characters, not bytes, as described on ed(1). String comparisons are affected by the LC_COLLATE and LC_CTYPE environment variables (see LANG on environ(5)).

Errors

As a side effect of expression evaluation, expr returns the following exit values:

0: The expression is neither null nor 0.
1: The expression is null or 0.
2: An expression is invalid.
non-numeric argument: arithmetic attempted on a non-numeric string

Files

/usr/lib/locale/locale/LC_MESSAGES/uxcore.abi: language-specific message file (See LANG on environ(5).)

Usage

Examples

Add 1 to the shell variable a:

a=`expr $a + 1`

The following example emulates basename(1); it returns the last segment of the path name $a. For $a equal to either /usr/abc/file or just file, the example returns file. The // characters eliminate any ambiguity about the division operator.

expr //$a : '.*/$.*$'

Notices

After argument processing by the shell, expr cannot tell the difference between an operator and an operand except by the value. If $a is an ``='', the command:

expr $a = '='

looks like:

expr = = =

as the arguments are passed to expr (and they are all taken as the = operator). The following works:

expr X$a = X=