use strict;
use warnings;

my $fname = 'myfile';
my $limit = 50 * 1024;
my ($size, $fc, $handle, $printstr) = (0, 1);

open ($handle, ">$fname$fc");
for (1..100) {
    $printstr = '-'x1000 . "\n";
    if ($limit < $size + length($printstr)) {
        close($handle);
        $size = 0; $fc++;
        open ($handle, ">$fname$fc");
    }
    print $handle $printstr;
    $size += length($printstr);
}
close($handle);