When you need to ensure that you have a unique list consider using

if (! $elements{$x}){ # we haven't seen it before
   $elements{$x}=1;
}
else{
   print "Seen it\n";
}
print join ",", keys(%elements);
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As for your original question, sending an end of file to STDIN has no effect on while(1) you could read each line from STDIN until you hit an end of file.