It has been pointed out that you should use split() but if you'd rather use match:

my $semiColon=2;
my ($substring) = $string =~ /(?:;.*?){$semiColon}(.*?);/;
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If you want to find the n^th piece of a m-piece string where n << m it can make sense to use the match approach.

Note: $substring will be undef is $string contained fewer then $semiColon+1 semicolons.

Update: Correction, I meant where n and m are both large. If n is small then simply use the LIMIT arg of split!