What typing ^D does on Unix (2009)
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What typing ^D does on Unix (2009)
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Re: What typing ^D does on Unix (2009)
#2As a corollary, typing ^D twice on a non-empty line will also send EOF on the input, allowing you to provide a program with input not ending with \n from the command line. I knew about this behavior, but not why it worked, but this article's explanation clarifies this behavior as well. The first ^D terminates the read() call, passing the line so far, without terminating \n, to the program. The second causes read() to return with 0 read bytes, which is EOF, as explained in the article.
Re: What typing ^D does on Unix (2009)
#3huh. That's really interesting. I assume ^L is handled in the tty driver as well?
Re: What typing ^D does on Unix (2009)
#4huh. That's really interesting. I assume ^L is handled in the tty driver as well?
^L usually has no assigned action.
$ stty -a | grep -F '^D'
intr = ^C; quit = ^\; erase = ^?; kill = ^U; eof = ^D; eol = ;
$ stty -a | grep -F '^L'
$
There is a "reprint" action, commonly bound to ^R:
$ stty -a | grep rprnt
eol2 = ; swtch = ; start = ^Q; stop = ^S; susp = ^Z; rprnt = ^R;
Re: What typing ^D does on Unix (2009)
#5^U will clear the buffer - super convenient for retrying botched passwords.
Re: What typing ^D does on Unix (2009)
#6Pressing enter then ~. will gracefully shutdown hung ssh sessions
Re: What typing ^D does on Unix (2009)
#7Pressing enter then ~. will gracefully shutdown hung ssh sessions
nice one, never seen that - always used ^D/exit
Re: What typing ^D does on Unix (2009)
#8huh. That's really interesting. I assume ^L is handled in the tty driver as well?
An important upshot is that TTY I/O never actually ends; EOF from a TTY is a temporary condition, and input can continue.
In the C standard library, you just clearerr(stdin) and keep reading.
If a program takes two files as input and obeys the - convention for specifying stdin (or has some other way of opening the tty more than once), you can do:
$ program - -
This sort of thing subtly breaks with some utilities. Try coaxing GNU diff to compare two pieces of tty input, haha.
Re: What typing ^D does on Unix (2009)
#9Pressing enter then ~. will gracefully shutdown hung ssh sessions
nice one, never seen that - always used ^D/exit
Those are yet more graceful -- for when the shell is responsive. Use ~. in cases where for some reason you cannot get access to the terminal anymore but remote sshd is responsive.
Re: What typing ^D does on Unix (2009)
#10Earlier quoted context omitted.
nice one, never seen that - always used ^D/exit
Those are yet more graceful -- for when the shell is responsive. Use ~. in cases where for some reason you cannot get access to the terminal anymore but remote sshd is responsive.
iirc, enter-~-. isn't anything to do with the remote sshd. Instead, it escapes to the local ssh client (enter-~) that it should close (.). Which is really useful for if the remote sshd blew up, or, more commonly, your connection was broken.