Something extensible .. more coding efficient, but not necessarily less execution time ... 
use strict;

my %actionlist=(
  "you have to read the fourth line" => 4,
  "you have to read the second line" => 2
  );
my $re = "(" . join ("|", keys %actionlist) . ")";
$re= qr|$re|;

  my $printthis = -1;    
  while (<DATA>){
    if (my ($match) = /$re/){
       $printthis = $actionlist{$match};
   }    
   $printthis-- == 0 and print;
  }      

__DATA__
first line
second line
third line
you have to read the fourth line
one
two
three
four
five
six
you have to read the second line
one
two
three

[download]
Update: On reflection, this solution is very similar to jwkrahn's.

     ..to maintain is to slowly feel your soul, sanity and sentience ebb away as you become one with the Evil.

In reply to Re: Reading nth line from a file by NetWallah
in thread Reading nth line from a file by perlthirst

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