What is the difference between the following two shell arithmetic commands:echo $[ $var1 - 1 ]echo $(( $var1 - 1 ))Assuming var1 = 5 for example.
Difference between two types of shell arithmetic
bash;shell script;arithmetic
From man bash:Arithmetic Expansion   Arithmetic expansion allows the evaluation of an arithmetic    expression and the substitution of the result.  The format    for arithmetic expansion is:          $((expression))   The old format $[expression] is deprecated and will be    removed in upcoming versions of bash.