Just a small alteration changing the hard coded 12 to something random:

use strict;
my $target = sprintf "%.$_[1]f", rand(10);
print "Guess my number.\n";

while ((print "Enter your guess: "), my $guess = <STDIN>)
  {
  (print "You guessed it!"), last if $guess == $target;
  (print "You guessed too low\n"), next if $guess < $target;
  (print "You guessed too high\n"), next if $guess > $target;
  }
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