I can't tell you why the backref doesn't work in a quantifier... but you could use the "postponed regex" construct (??{ code }): 

my ($n, $v) = "3 aaa " =~ /^(\d+?) ((??{".{$1}"})) /;

print "n=$n, v=$v\n";   # prints "n=3, v=aaa"

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In reply to Re: Backref in a regex quantifier by almut
in thread Backref in a regex quantifier by Anonymous Monk

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