my $file = 'foo.txt';

one();
two();
two();
one();

sub one {
    open my $fh, "+>", $file or die $!;
    print $fh "Hello World!\n";
    seek $fh, 0, 0;
    print while <$fh>;
    close $fh;
    print "--\n\n";
}

sub two {
    open my $fh, "+>>", $file or die $!;
    print $fh "japh!\n";
    seek $fh, 0, 0;
    print while <$fh>;
    close $fh;
    print "--\n\n";
}

__DATA__
Hello World!
--

Hello World!
japh!
--

Hello World!
japh!
japh!
--

Hello World!
--
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