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 string regular-expression
The two forms of the matching operator are synonymous. 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), expect that the pattern is always anchored to the beginning of the string (that is, there is always an implicit ‘^’ at the start of the regular expression). The \(...\) pattern symbols can be used to return a portion of the first argument.  Otherwise, the matching operator yields the number of characters matched (‘0’ on failure). 

substr string start length
extracts the portion of string which begins at position start and is length characters long.  If start is greater than the length of string, then a null string is returned.  If you try to extract more characters than are present, then all the characters from start to the end of the string are returned.  The positions are numbered starting at 1.  Do not pass negative values for start or length.

index string chars
returns the first position in string at which any of the characters in chars occurs. 

length string
returns the length of the 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  —  Revision 1.3 of 10/10/90