stty hupcl ixon ixoff

Question

I'm seeing stty, not a typewritter messages on hpux (despite an interactive terminal check?), and am guessing that these are due to the stty lines in my .kshrc file:

case $- in
*i* )
    stty hupcl ixon ixoff
    stty erase '^?' kill '^U' intr '^C' eof '^D' susp '^Z'
;;
esac

Two questions:

1) I know why the erase line is there, since backspace doesn't work without it. These .kshrc lines I've inherited, but don't know what they do.

Anybody know the point of the hupcl ixon ixoff lines? The stty man page isn't particularly enlightening:

hupcl (-hupcl)           Hang up (do not hang up) modem connection on
                         last close.

ixon (-ixon)             Enable (disable) START/STOP output control.
                         Output is stopped by sending an ASCII DC3 and
                         started by sending an ASCII DC1.

ixoff (-ixoff)           Request that the system send (not send)
                         START/STOP characters when the input queue is
                         nearly empty/full.

2) Is there a different way to check for interactive terminals. I had tty -s ; if [ $? ] before but that also appears to be noisy on hpux.

Vanvanadate

Answer 1

ixon and ixoff are used to insist that Ctrl-s and Ctrl-q be interpreted as control flow (scroll lock) signals. They're the default on most systems, but if you have a fast connection and/or don't anticipate a volume of output that your terminal can't handle, you're fine to turn them off.

I typically use stty -ixon -ixoff so I can reclaim the Ctrl-s and Ctrl-q key bindings for more modern purposes (e.g. "save" and "quit").

For more details: https://unix.stackexchange.com/questions/12107/how-to-unfreeze-after-accidentally-pressing-ctrl-s-in-a-terminal#12146

Utile

Is ixon for CTRL-S and ixoff for CTRL-Q? – Kimberliekimberlin

@Kimberliekimberlin - stty ixon enables the freeze/unfreeze behavior for both CTRL-S and CTRL-Q, and stty -ixon disables that behavior. stty ixoff is not related to CTRL-S and CTRL-Q – Bellied

"stty ixoff is not related to CTRL-S and CTRL-Q", so what is ixoff for ? – Bab

Answer 2

\1.

As you've inherited your .kshrc, there might have been a reason that at one time you system needed those extra hupcl, ixon, ixoff parameters. They might be obsolete now, but they might be something that is HP centric. OR it could be that some application works better with them included. Maybe an ol' timer will know.

Anybody know the point of the hupcl ixon ixoff lines

To me those descriptions are pretty self evident, but then I have had to deal with such issues way----yyyy back, and read the Orielly termcap & terminfo to sort it out. You can look at man ascii to see DC3 and DC1 in their context, or google searches might get you something interesting.

Now a-days, I would expect that unless you have special needs, that these aren't really helping you. Do you have special HP hardware or special terminfo applications. If not, try commenting that line out.

\2. Test for interactive

I like your case $- in *i* ... that should be good enough.

else

  if tty -s > /dev/null 2>&1 ; then ...

might be help

OR the cannonical

  if [[ -t 0 ]]; then

I hope this helps.

Glomeration

Thanks. That's probably about as good an answer as is possible. I hope to not have to read that book though;) – Vanvanadate