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.
1 z=`expr $z + 3` # The 'expr' command performs the expansion.
The use of backticks in arithmetic expansion has been superseded by double parentheses $((...)) or the very convenient let construction.
1 z=$(($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: