my $filepath = 'foo.txt';

open my $FOOFILE, '>>', $filepath or die "Couldn't open $filepath: $!\n";
print $FOOFILE "First line of text.\n";

for (1 .. 5) {
    #do a bunch of stuff
    do_other_stuff ($FOOFILE);
}

print $FOOFILE "The end.";
close $FOOFILE;