EXPR

Section: User Commands (1)
Updated: April 29, 1985
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NAME

expr - evaluate arguments as an expression

SYNOPSIS

expr arg ...

DESCRIPTION

The arguments are taken as an expression. After evaluation, the result is written on the standard output. Each token of the expression is a separate argument.

The operators and keywords are listed below. The list is in order of increasing precedence, with equal precedence operators grouped.

expr | expr: yields the first expr if it is neither null nor `0', otherwise yields the second expr.
expr & expr: yields the first expr if neither expr is null or `0', otherwise yields `0'.
expr relop expr: where relop is one of < <= = != >= >, yields `1' if the indicated comparison is true, `0' if false. The comparison is numeric if both expr are integers, otherwise lexicographic.
expr + expr
expr - expr: addition or subtraction of the arguments.
expr * expr
expr / expr
expr % expr: multiplication, division, or remainder of the arguments.
expr : expr: The matching operator compares the string first argument with the regular expression second argument; regular expression syntax is the same as that of ed(1). The $...$ pattern symbols can be used to select a portion of the first argument. Otherwise, the matching operator yields the number of characters matched (`0' on failure).
( expr ): parentheses for grouping.

Examples:

To add 1 to the Shell variable a:

: a=`expr $a + 1`

To find the filename part (least significant part) of the pathname stored in variable a, which may or may not contain `/':

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

Note the quoted Shell metacharacters.

DIAGNOSTICS

Expr returns the following exit codes:

       0       if the expression is neither null nor `0',

       1       if the expression
is null or `0',
       2       for invalid expressions.