Is there any significant difference between using [[ $a -lt 2 ]] and (( $a < 2 ))? For example, is one of them faster or more POSIX compliant than the other?
Difference between `[[ $a -lt 2 ]]` and `(( $a < 2 ))`
bash;test
Neither is POSIX-compatible. In a POSIX shell, you can use the command [ $a -lt 2 ] or the expression $(( a < 2 )).In bash, the former is simply the conditional command supporting a superset of the conditional expressions that [ supports, and the latter is a standalone command that exits with status 0 if the enclosed arithmetic expression is non-zero, or 1 otherwise. Other than readability, there is no significant difference between the two when used properly.