You can also use the \Q and \E in the regular expression to make sure charaters are interpreted literally;

$delimeter = "+";
$t = "t+e+s+t";
($a, $b, $c, $d) = split(/\Q$delimeter\E/, $t);

### or ###
($a, $b, $c, $d) = split(/\Q+\E/, $t);
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But for the last one just using /\+/ is obviously easier.