Make use of the either quotemeta or the regex equivalent \Q (see. perlre for more info on \Q). So something like 
if ($concat !~ /\Q$string/) {
   $concat .= " and $string";
}

[download]

HTH

_________
broquaint

In reply to Re: Escaping parentheses in regexps by broquaint
in thread Escaping parentheses in regexps by Tanalis

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