A bashism a week: maths

You've probably already done some basic maths in shell scripts, but do you know what else you can actually do?

Pick at least 4 operations that you can do in bashisms-free shell scripts:

$((n+1))
$((n>8))
$((n^4))
$((--n))
$((n*=5))
$((n++))
$((n==1?2:3))

The POSIX:2001 standard defines the arithmetic expansion requirements, which leads us to selecting all of the above operations except two:

$((--n))
$((n++))

"--" and "++" are not required to be implemented, and in some cases they may lead to unexpected results, such as the following:


$ bash -c 'n=1; echo $((++n))'
2
$ dash -c 'n=1; echo $((++n))'
1


Remember, if you rely on any non-standard behaviour or feature make sure you document it and, if feasible, check for it at run-time.