36.21.1. Syntax

expr arg1 operator arg2 [ operator arg3 ... ]

Arguments and operators must be separated by spaces. In many cases, an argument is an integer, typed literally or represented by a shell variable. There are three types of operators: arithmetic, relational, and logical.

36.21.2. Examples

$ expr 5 + 10 / 2

Addition happens first; output is 7 (truncated from 7.5):

$ expr \( 5 + 10 \) / 2

Add 1 to variable i; this is how variables are incremented in Bourne shell scripts:

i=`expr "$i" + 1`

$ expr "$a" = hello

Output 1 (true) if variable b plus 5 equals 10 or more:

$ expr "$b" + 5 \>= 10

In the examples below, variable p is the string "version.100". This command returns the number of characters in p:

$ expr "$p" : '.*'           Output is 11

Match all characters and print them:

$ expr "$p" : '\(.*\)'       Output is "version.100"

Output the number of lowercase letters matched:

$ expr "$p" : '[a-z]*'       Output is 7

Match a string of lowercase letters:

$ expr "$p" : '\([a-z]*\)'   Output is "version"

Truncate $x if it contains five or more characters; if not, just output $x. (Logical OR uses the second argument when the first one is 0 or null, i.e., when the match fails.)

$ expr "$x" : '\(.....\)'  "$x"