Re: misbehavior in shell window with ksh

[Mike Kupfer <mkupfer@alum.berkeley.edu>]

Eli Zaretskii wrote:

> Can the shell experts among us please tell whether this is an expected
> reaction of a shell to window-resizing ioctl?  And why this is only
> seen with ksh?  And why in some cases one needs to set EDITOR in the
> environment?

I'm not a shell expert, but I did spend a little time with strace to see
what ksh is doing.

In a regular terminal emulator (xfce4-terminal), when ksh gets SIGWINCH,
it queries for the size of the screen, and it generates one or more
carriage returns before (re)writing the PS1 prompt.

  --- SIGWINCH {si_signo=SIGWINCH, si_code=SI_KERNEL} ---
  rt_sigaction(SIGWINCH, {0x41c250, [], SA_RESTORER|SA_INTERRUPT, 0x7f91cb7cd0e0}, {0x41c250, [], SA_RESTORER|SA_INTERRUPT, 0x7f91cb7cd0e0}, 8) = 0
  ioctl(2, TIOCGWINSZ, {ws_row=25, ws_col=80, ws_xpixel=0, ws_ypixel=0}) = 0
  rt_sigprocmask(SIG_UNBLOCK, [WINCH], NULL, 8) = 0
  rt_sigreturn()                          = -1 EINTR (Interrupted system call)
  write(2, "\r", 1)                       = 1
  ioctl(2, TIOCGWINSZ, {ws_row=25, ws_col=80, ws_xpixel=0, ws_ypixel=0}) = 0
  poll(0x7ffcc1e41dc0, 0, 50)             = 0 (Timeout)
  ioctl(2, TIOCGWINSZ, {ws_row=25, ws_col=80, ws_xpixel=0, ws_ypixel=0}) = 0
  write(2, "\ralto$ ", 7)                 = 7
  select(1, [0], NULL, NULL, NULL)        = ? ERESTARTNOHAND (To be restarted if no handler)

Its behavior in a shell buffer is similar, except it just writes out the
PS2 prompt.

  --- SIGWINCH {si_signo=SIGWINCH, si_code=SI_KERNEL} ---
  rt_sigaction(SIGWINCH, {0x41c250, [], SA_RESTORER|SA_INTERRUPT, 0x7fc02802d0e0}, {0x41c250, [], SA_RESTORER|SA_INTERRUPT, 0x7fc02802d0e0}, 8) = 0
  ioctl(2, TIOCGWINSZ, {ws_row=32, ws_col=78, ws_xpixel=0, ws_ypixel=0}) = 0
  rt_sigprocmask(SIG_UNBLOCK, [WINCH], NULL, 8) = 0
  rt_sigreturn()                          = -1 EINTR (Interrupted system call)
  ioctl(2, TIOCGWINSZ, {ws_row=32, ws_col=78, ws_xpixel=0, ws_ypixel=0}) = 0
  poll(0x7ffc9eb5abf0, 0, 50)             = 0 (Timeout)
  ioctl(2, TIOCGWINSZ, {ws_row=32, ws_col=78, ws_xpixel=0, ws_ypixel=0}) = 0
  select(1, [0], NULL, NULL, {0, 0})      = 0 (Timeout)
  write(2, "> ", 2)                       = 2

I can't explain the difference.

I also checked bash's behavior.  It does not query the current screen
size.

bash in an Emacs shell buffer:

  read(0, 0x6fdc00, 128)                  = ? ERESTARTSYS (To be restarted if SA_RESTART is set)
  --- SIGWINCH {si_signo=SIGWINCH, si_code=SI_KERNEL} ---
  rt_sigreturn()                          = -1 EINTR (Interrupted system call)
  read(0,  <detached ...>

bash in an xfce4-terminal:

  read(0, 0x7ffd51136837, 1)              = ? ERESTARTSYS (To be restarted if SA_RESTART is set)
  --- SIGWINCH {si_signo=SIGWINCH, si_code=SI_KERNEL} ---
  rt_sigreturn()                          = 0
  read(0, 0x7ffd51136837, 1)              = ? ERESTARTSYS (To be restarted if SA_RESTART is set)
  [...]
  --- SIGWINCH {si_signo=SIGWINCH, si_code=SI_KERNEL} ---
  rt_sigreturn()                          = 0
  read(0, 0x7ffd51136837, 1)              = ? ERESTARTSYS (To be restarted if SA_RESTART is set)
  --- SIGWINCH {si_signo=SIGWINCH, si_code=SI_KERNEL} ---
  rt_sigreturn()                          = 0
  read(0, 0x7ffd51136837, 1)              = ? ERESTARTSYS (To be restarted if SA_RESTART is set)
  --- SIGWINCH {si_signo=SIGWINCH, si_code=SI_KERNEL} ---
  rt_sigreturn()                          = 0
  read(0,  <detached ...>

regards,
mike