Use $istok, and you should use return instead of halt here, i'm sure you don't need to stop the whole script.
Code:
on *:TEXT:!command*:*:{
if (!$istok(-cm1 -cmd2 -cm3,$2,32)) msg $nick Usage : !command -cm1, -cm2 or -cm3
else {
;your script here
 }
}

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