. to end input is a rather old tradition in computing, which in turn is as yet young.

    $ ed
    a
    pending thought is good to have
    between the lines we hold so dear
    but yet to disk these bytes are saved
    and float like ether from a pier

    hey! diddle dot dash, sang the mime
    whose work here is as yet unclear
    perhaps it was to close a rhyme
    or add more verse as we now fear

    now mimes and clowns are much the same
    poor sailors do they make of sea
    on ether waves they run git blame
    and from a pipe they drink to tea!

    with fish to catch and skel in tow
    and dreams of lions ever sought
    they ply their lines with naught to show
    while sings the mime--hey! diddle
    .
    a
    x
    .
    s/x/.
    .
    0a
    a
    .
    f poem
    poem
    wq
    562
    $ cat poem
    a
    pending thought is good to have
    between the lines we hold so dear
    but yet to disk these bytes are saved
    and float like ether from a pier

    hey! diddle dot dash, sang the mime
    whose work here is as yet unclear
    perhaps it was to close a rhyme
    or add more verse as we now fear

    now mimes and clowns are much the same
    poor sailors do they make of sea
    on ether waves they run git blame
    and from a pipe they drink to tea!

    with fish to catch and skel in tow
    and dreams of lions ever sought
    they ply their lines with naught to show
    while sings the mime--hey! diddle
    .

The dot appears in other protocols, SMTP for example.

    $ telnet localhost 25
    Trying 127.0.0.1...
    Connected to localhost.
    Escape character is '^]'.
    220 gear.thrig.me ESMTP OpenSMTPD
    HELO nurse
    250 gear.thrig.me Hello nurse [127.0.0.1], pleased to meet you
    MAIL FROM:<jmates>
    250 2.0.0 Ok
    RCPT TO:<jmates>
    250 2.1.5 Destination address valid: Recipient ok
    DATA
    354 Enter mail, end with "." on a line by itself
    Subject: test

    test
    .
    250 2.0.0 3d7ff7fa Message accepted for delivery
    QUIT
    221 2.0.0 Bye
    Connection closed by foreign host.

This obviously means that no line may contain . by itself. Those ahead of the curve might think to send an email that contains a . on a line by itself and then be all like "you wrong!". Hopefully they remembered to send a plaintext email, not one janked up with HTML, and for those ahead of that curve they may already know section 4.5.2 of RFC 5321.

https://useplaintext.email/

    rsync --exclude=.DS_Store -avz --delete --delete-excluded ftp.rfc-editor.org::rfcs-text-only rfcs

Another method is to base64 encode the whole message, as base64 cannot generate a . on a line by itself. This however embiggens the message and may annoy certain plaintext email users, or the non-zero number of programmers who assumed that the message would not be so encoded.

    $ echo . | openssl base64
    Lgo=

The dot can also close a SSH connection, though must follow ~ and only at the beginning of a line, and assuming the EscapeChar has not been changed from the default, diddle dot!

gemini://idiomdrottning.org/molly-metcalfe

tags #poetry #ed #rfc #smtp