expr

SYNOPSIS

expr expression

DESCRIPTION

The expr(1) utility parses an expression provided as arguments and prints the result on the standard output.

The expr(1) utility recognizes three types of operators: relational operators, arithmetic operators and string operators. The following left-associative binary operators are listed from lowest to highest precedence:

expr | expr: Yields the first expr if it is neither null nor 0; otherwise, it yields the second expr.
expr & expr: Yields the first expr if neither expr is null or 0; otherwise, it yields 0.
expr relop expr: Where relop is one of <, <=, =, !=, >=, or >, yields 1 if the indicated comparison is true; it yields 0 if false. The comparison is numeric if the two expressions are integers; otherwise, it is 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: The matching operator compares the string first argument with the regular expression second argument; regular expression matching is the same as the ed(1) editor. The \( \) pattern symbols can be used to select a portion of the first argument. Otherwise, the matching operator yields the number of characters matched (0 on failure).
( expr): Parentheses for grouping expressions.

DIAGNOSTICS

The expr(1) utility exits with 0 if the expression is neither null nor 0, exits with 1 if the expression is null or 0, and exits >1 if there is an error in the expression.

EXAMPLES

A simple arithmetic calculation; the answer is 8, because division is performed first.

$ expr 4 + 8 / 2
8

Check to see if the value of variable input is hello:

$ expr "$input" = "hello"

List the number of characters in the first directory in your PATH:

$ expr 'echo $PATH' : \[^:]*

Extract the first directory in your PATH; both characters in \( need to be escaped for the shell. An alternate form using single quotes instead of backslashes is also shown:

$ expr "$(echo $PATH)" : \\\(\[^:]*\\\):.*
$ expr "$(echo $PATH)" : '\(\[^:]*\):.*'

When matching strings, expr(1) is best for breaking a string into two parts; it is not very useful for extracting a particular word.

NOTES

Many of the operators are special to the shell and must be quoted.

Operators cannot be used as (string) operands.