**let**

*expressions*
or

**((**

*expressions*
**))**

Korn shell only. 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" earlier in this chapter. See also **expr**
in Chapter 2
.

Each of these examples adds 1 to variable **i**

:

i=`expr $i + 1` *sh, ksh88, ksh93*
let i=i+1 *ksh88 and ksh93*
let "i = i + 1"
(( i = i + 1 ))
(( i += 1 ))
(( i++ )) *ksh93 only*