$ cat file_gen.pl
#!/usr/bin/env perl
use strict;
use warnings;

open my $FH, '>', 'a_file.txt';
$|=1;
for (1 .. 1000) {
    print $FH "$_: here's 80 stars: ", "*"x80, "\n";
    my $t = time;
    print "$t: line: $_\n";
    sleep 1;
}

##</code><code>##

#!/usr/bin/env perl
use strict;
use warnings;

while (1) {
    my $t = time;
    print "$t: Here's what we have so far:\n";
    open my $FH, '<', 'a_file.txt';
    my @lines = <$FH>;
    close $FH;
    print join("", @lines),"\n";
    sleep 5;
}