Chapter 15. Arithmetic Expansion

Variations

Arithmetic expansion with backticks (often used in conjunction with expr)

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The use of backticks in arithmetic expansion has been superseded by double parentheses $((...))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.

z=$(($z+3)) # $((EXPRESSION)) is arithmetic expansion. # Not to be confused with #+ command substitution. let z=z+3 let "z += 3" # Quotes permit the use of spaces and special operators. # The 'let' operator actually performs arithmetic evaluation, #+ rather than expansion.

All the above are equivalent. You may use whichever one "rings your chimes".

Examples of arithmetic expansion in scripts:

1. Example 12-6

2. Example 10-14

3. Example 26-1

4. Example 26-6

5. Example A-18