#!/usr/bin/perl

use strict;

# initially, create a scalar that is 1 line long
my $line = ">"."\n" x 1;
my $incr = 1;

while (1) { # run until it crashes

   while ($line =~ /^(>.*)\n(^(?!>).*\n)+/gm) {
      print "Number of lines: ", length($line)-1,"\n";
   }

   # add another line
   $line .= "\n" x $incr;
}