Korn shell only. Perform arithmetic as specified by one or more integer
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 section.
See also expr in Section 2.
Each example below adds 1 to variable i.
i=`expr $i + 1` let i=i+1 let "i = i + 1" (( i = i + 1 ))