my ($x,$y) = ($string =~ /^(.{n})(.{n})/);
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This will put the 1st n char into $x and the 2nd n chars into $y without touching $string... if you want the rest of the chars:

my ($x, $y, $rest) = ($string =~ /^(.{n})(.{n})(.*)/);
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if you don't like regexp's you can allways try substr