expr

Usage: expr EXPRESSION

Prints the value of EXPRESSION to standard output.

EXPRESSION may be:

			ARG1 |  ARG2    ARG1 if it is neither null nor 0, otherwise ARG2
			ARG1 &  ARG2    ARG1 if neither argument is null or 0, otherwise 0
			ARG1 <  ARG2    ARG1 is less than ARG2
			ARG1 <= ARG2    ARG1 is less than or equal to ARG2
			ARG1 =  ARG2    ARG1 is equal to ARG2
			ARG1 != ARG2    ARG1 is unequal to ARG2
			ARG1 >= ARG2    ARG1 is greater than or equal to ARG2
			ARG1 >  ARG2    ARG1 is greater than ARG2
			ARG1 +  ARG2    arithmetic sum of ARG1 and ARG2
			ARG1 -  ARG2    arithmetic difference of ARG1 and ARG2
			ARG1 *  ARG2    arithmetic product of ARG1 and ARG2
			ARG1 /  ARG2    arithmetic quotient of ARG1 divided by ARG2
			ARG1 %  ARG2    arithmetic remainder of ARG1 divided by ARG2
			STRING : REGEXP             anchored pattern match of REGEXP in STRING
			match STRING REGEXP         same as STRING : REGEXP
			substr STRING POS LENGTH    substring of STRING, POS counted from 1
			index STRING CHARS          index in STRING where any CHARS is found, or 0
			length STRING               length of STRING
			quote TOKEN                 interpret TOKEN as a string, even if it is a
							keyword like `match' or an operator like `/'
			( EXPRESSION )              value of EXPRESSION
		

Beware that many operators need to be escaped or quoted for shells. Comparisons are arithmetic if both ARGs are numbers, else lexicographical. Pattern matches return the string matched between \( and \) or null; if \( and \) are not used, they return the number of characters matched or 0.