Expr


expr is a command line Unix utility which evaluates an expression and outputs the corresponding value. It first appeared in Unix v7.

Overview

expr evaluates integer or string expressions, including pattern matching regular expressions. Each symbol in the expression must be given as a separate parameter. Most of the challenge posed in writing expressions is preventing the invoking command line shell from acting on characters intended for expr to process.

Syntax

Syntax: expr expression
The operators available
The following is an example involving boolean expressions:
expr length "abcdef" "<" 5 "|" 15 - 4 ">" 8
This example outputs "1". This is because length "abcdef" is 6, which is not less than 5. But 15 minus 4 is 11 and is greater than 8, so the right side is true, which makes the or true, so 1 is the result. The program exit status is zero for this example.
For pure arithmetic, it is often more convenient to use bc. For example:
echo "3*4+14/2" | bc
since it accepts the expression as a single argument.
For portable shell programming use of the length and substr commands is not recommended.