. 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.
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