As a crude one liner perl -e 'while (<>){if ($. > 5){print $_;}}' file >file.tmp;mv file.tmp file

To add sophistication print to a file handle, ie

use strict;
use warnings;
my ($FILE, $TEMP);
open $FILE, "<", "file";
open $TEMP,">",file.tmp;
while (<$FILE>){
   if ($. > 5){
      print $TEMP $_;
   }
}
close $FILE;
close $TEMP;
rename file.tmp, file;
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