use strict;
use warnings;
use Tie::File;
use Fcntl 'O_RDONLY';

my $file = 'screenlog';

unlink $file;

tie my @lines, 'Tie::File', "$file.0", mode => O_RDONLY;

my $end = (scalar @lines > 200 ? 200 : scalar @lines);  # added

open(OUT,">",$file) or die("Unable to open $file: $!");
print OUT join "\n", @lines[-$end..-1];                 # changed
close OUT;

untie @lines;