bash Quick Reference

Name

let

Synopsis

let expressions
(( expressions ))

Perform arithmetic as specified by one or more expressions. expressions consist of numbers, operators, and shell variables (which don't need a preceding $). Expressions must be quoted if they contain spaces or other special characters. The (( )) form does the quoting for you. For more information and examples, see the section Arithmetic Expressions, earlier in this reference. See also expr(1).

Examples

Each of these examples adds 1 to variable i:

i=`expr $i + 1`         All Bourne shells
let i=i+1               Bash
let "i = i + 1"
(( i = i + 1 ))
(( i += 1 ))
(( i++ ))