Linux in a Nutshell, 6th Edition

Name

let

Synopsis

let expressions
or
((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 Arithmetic Expressions in Arithmetic Expressions. See also expr in Chapter 3.

Examples

Each of these examples adds 1 to variable i:

i=`expr $i + 1`
let i=i+1
let "i = i + 1"
(( i = i + 1 ))
(( i += 1 ))
(( i++ ))