use warnings;
use strict;
use autodie;

open IN, "<file.txt";
binmode IN;
my @content = <IN>;
close IN;

foreach my $num (keys %rec) {
    my @count = ("@content" =~ /$num+/sg);
    open my $fh, ">iterations$num.txt";
    print "$_\n" for @count;
    close $fh;
}