Tests

expr

expr expression

Expr returns 0 if expression is neither null or 0, 1 if the expression is null or 0, and 2 for an invalid expression.

test if ARG1 is less than ARG2

expr 7 \< 3

add 1 to a number (and write the result to stdout)

expr $number + 1

match a substring

expr match "hello world" '.*ello wo'

returns 8

expr match "hello world" 'ello wo'

returns 0

index where a substring is found, else 0

expr index "this is an example" e

returns 12