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

match expr expr
compares the first argument (a string) with the second argument (a regular expression); 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, this operator yields the number of characters matched (‘0’ on failure). 

index expr expr
finds the second argument (a string) in the first. Returns the location of the first matched character (where the first character is at location ‘1’) or ‘0’ if the second argument is not a substring of the first.

substr expr expr expr
returns the substring of the first argument (a string) that starts at the position specified by the second argument (where ‘1’ refers to the first character) and has length equal to the third argument (a numeral).

length expr
returns the length of the argument (a string).

( 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. 

SEE ALSO

sh(1), test(1)

DIAGNOSTICS

Expr returns the following exit codes:

0if the expression is neither null nor ‘0’,
1if the expression is null or ‘0’,
2for invalid expressions. 

7th Edition  —  April 29, 1985