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)
1 z=`expr $z + 3` # The 'expr' command performs 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**let** The use of backticks in arithmetic expansion has been superseded by double parentheses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".1 z=$(($z+3)) 2 # $((EXPRESSION)) is arithmetic expansion. # Not to be confused with 3 #+ command substitution. 4 5 let z=z+3 6 let "z += 3" # Quotes permit the use of spaces and special operators. 7 # The 'let' operator actually performs arithmetic evaluation, 8 #+ rather than expansion.

Examples of arithmetic expansion in scripts: