Either write 
for (grep {$links{$_}{visited}} keys %links) {
   #....
}

[download]
or, a bit more efficient, 
for (keys %links) {
  if ($links{$_}{visited}) {
   #....
  }
}

[download]

Courage, the Cowardly Dog

In reply to Re: Creating loop on undefined hash key value by Courage
in thread Creating loop on undefined hash key value by S_Shrum

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