your code is probably better implemented as a closure. then there's no special variable in the same scope as your code.

{
  my $num_ctrlc = 0;
  $SIG{'INT'} = sub {
    print "Got " . ++$num_ctrlc . " ctrl-c\n";
    exit if $num_ctrlc > 2;
  }
}
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~Particle *accelerates*