if ($value =~ /\/|;|#|!|"|'|`|\|)/) {
   print "Invalid parameter";
   # perhaps log this "malicious" attempt
} else {
   processhappily();
}
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Don't forget to escape those characters with a \. I usually escape all my non-alphanumerics with a \ because I can't remember which ones are special in regexs (I have my O'Reilly book in front of my now, they're \ | ( ) [ { ^ $ * + ? . but I usually play it safe. Also, but the O'Reilly book if you're new. It's great help