expr

expr

Original author(s)	Dick Haight
Developer(s)	AT&T Bell Laboratories
Initial release	1979 (1979)
Operating system	Unix and Unix-like
Type	Command

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 (operator, value, etc.) 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

• for integers: addition, subtraction, multiplication, division and modulus
• for strings: find regular expression, find a set of characters in a string; in some versions: find substring, length of string
• for either: comparison (equal, not equal, less than, etc.)

Example

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 (so the left side of the | returns zero). 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.

See also

• List of Unix commands

External links

• expr: evaluate arguments as an expression – Shell and Utilities Reference, The Single UNIX Specification, Version 4 from The Open Group
• expr invocation in GNU coreutils manual