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.