my %set #how you initialize an array
while($line=<>) #while text is coming in from the keyboard 
                #set $line=line of keyboard input
{
    unless($set{$line}){
      $set{$line}=1;  # basically means we've seen this line
    }
}

#now lets see each $line we've encountered
foreach my $line(keys %set){
   print $line;
}