Arithmetic expansion provides a powerful tool for performing arithmetic operations in scripts. Translating a string into a numerical expression is relatively straightforward using backticks, double parentheses, or let.

- Arithmetic expansion with backticks (often used in conjunction with expr)
z=`expr $z + 3` # 'expr' does the expansion.

- Arithmetic expansion with double parentheses, and using
**let** The use of backticks in arithmetic expansion has been superseded by double parentheses

or the very convenient**$((...))****let**construction.

All the above are equivalent. You may use whichever one "rings your chimes".z=$(($z+3)) # $((EXPRESSION)) is arithmetic expansion. # Not to be confused with # command substitution. let z=z+3 let "z += 3" #If quotes, then spaces and special operators allowed. # 'let' is actually arithmetic evaluation, rather than expansion.

Examples of arithmetic expansion in scripts: