Bash operators

$()

The operator $() in the bash shell is replaced by the output of the command enclosed in the parentheses. It is equivalent to backticks (``), but can be cascaded more easily.

Examples:

rpm -ql $(rpm -qa)

for i in $(seq 1 1 100); do echo $i; done

$(())

The operator $(()) in the bash shell is replaced by the arithmetic result of the expression enclosed in the parentheses.

Examples:

# echo $((2*2))
4