use Proc::InvokeEditor;

my $unedited_text = read_text_from_existing_note('note.txt');
my $edited_text = Proc::InvokeEditor->edit($unedited_text);
write_text_to_existing_note('note.txt'); # update

# or alternatively
system($ENV{EDITOR}, '/tmp/note.txt') == 0
    or warn "Couldn't launch editor '$ENV{EDITOR}': $!";