Since you need to write the entire file to add to the front of it, just write 5 things back. Using truncate would actually be extra work. 

# Load old list.
my @sets = do {
   open(my $fh, '<', $file)
      or die("Unable to open set list \"$file\": $!\n");

   local $/ = '<br>';

   <$fh>
};

# Add new item to the top.
unshift @sets, "a new set - line 7<br>";

# Keep the top 5.
if (@sets > 5) {
   @sets = @sets[0..4];
}

# Save new list.
{
   open(my $fh, '>', $file)
      or die("Unable to create set list \"$file\": $!\n");

   print $fh @sets;
}

[download]

Update: Fixed indexes on slice.

In reply to Re: truncating a text file by ikegami
in thread truncating a text file by dankichi

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