keyboard input intercept

[RJ45]

Hello,
I am writing a shell in C.
I need to intercept Signals like CTRL+C or CTRL+D
and set to ignore them. This is on Unix, using gcc.
my goal is to avoid users escaping the shell with SIGINT
SIGQUIT signals using keyboard input.
Anyone could give me a little hint ?

thanks

Rick

[Ben Pfaff]

Re: keyboard input intercept

RJ45 <rj45@NOSPAMsla cknet.comwrites :

I am writing a shell in C.
I need to intercept Signals like CTRL+C or CTRL+D
and set to ignore them. This is on Unix, using gcc.
my goal is to avoid users escaping the shell with SIGINT
SIGQUIT signals using keyboard input.
Anyone could give me a little hint ?

I'd recommend comp.unix.progr ammer as a place where you're likely
to get better answers to this question.
--
Peter Seebach on C99:
"[F]or the most part, features were added, not removed. This sounds
great until you try to carry a full-sized printout of the standard
around for a day."

[santosh]

Re: keyboard input intercept

RJ45 wrote:

Hello,
I am writing a shell in C.
I need to intercept Signals like CTRL+C or CTRL+D
and set to ignore them. This is on Unix, using gcc.
my goal is to avoid users escaping the shell with SIGINT
SIGQUIT signals using keyboard input.
Anyone could give me a little hint ?
>
thanks
>
Rick

Yes, methods are available to do this, but you should ask in a group
for your system or atleast comp.unix.progr ammer, since it is system
specific. Standard C itself only provides rudimentary facilities for
signal handling, but your system's C library will most likely provide
more facilities to accomplish what you want.

[Kenny McCormack]

Re: keyboard input intercept

In article <slrneugmpc.nif .rj45@slacknet. com>,
RJ45 <rj45@NOSPAMsla cknet.comwrote:

>Hello,
>I am writing a shell in C.
>I need to intercept Signals like CTRL+C or CTRL+D
>and set to ignore them. This is on Unix, using gcc.
>my goal is to avoid users escaping the shell with SIGINT
>SIGQUIT signals using keyboard input.
>Anyone could give me a little hint ?

Let me be the first to say:

Off topic. Not portable. Cant discuss it here. Blah, blah, blah.

Useful clc-related links:

http://en.wikipedia.org/wiki/Aspergers

http://en.wikipedia.org/wiki/Clique

http://en.wikipedia.org/wiki/C_programming_language

However, I will point out, as a small hint, that ^C and ^D *aren't*
"signals". Grasping fully the implications of this will help greatly in
solving your underlying problem.

[Kenny McCormack]

Re: keyboard input intercept

In article <1172857020.529 340.316940@h3g2 000cwc.googlegr oups.com>,
santosh <santosh.k83@gm ail.comwrote:

>RJ45 wrote:

>Hello,
>I am writing a shell in C.
>I need to intercept Signals like CTRL+C or CTRL+D
>and set to ignore them. This is on Unix, using gcc.
>my goal is to avoid users escaping the shell with SIGINT
>SIGQUIT signals using keyboard input.
>Anyone could give me a little hint ?
>>
>thanks
>>
>Rick

>
>Yes, methods are available to do this, but you should ask in a group
>for your system or atleast comp.unix.progr ammer, since it is system
>specific. Standard C itself only provides rudimentary facilities for
>signal handling, but your system's C library will most likely provide
>more facilities to accomplish what you want.

But, as I pointed out, signal handling doesn't have anything to do with
it; *keyboard* handling does. I.e., OP certainly meant to write:

I need to intercept keys like CTRL+C or CTRL+D ...

[santosh]

Re: keyboard input intercept

Kenny McCormack wrote:

In article <1172857020.529 340.316940@h3g2 000cwc.googlegr oups.com>,
santosh <santosh.k83@gm ail.comwrote:

RJ45 wrote:

Hello,
I am writing a shell in C.
I need to intercept Signals like CTRL+C or CTRL+D
and set to ignore them. This is on Unix, using gcc.
my goal is to avoid users escaping the shell with SIGINT
SIGQUIT signals using keyboard input.
Anyone could give me a little hint ?
>
thanks
>
Rick

Yes, methods are available to do this, but you should ask in a group
for your system or atleast comp.unix.progr ammer, since it is system
specific. Standard C itself only provides rudimentary facilities for
signal handling, but your system's C library will most likely provide
more facilities to accomplish what you want.

>
But, as I pointed out, signal handling doesn't have anything to do with
it; *keyboard* handling does. I.e., OP certainly meant to write:
>
I need to intercept keys like CTRL+C or CTRL+D ...

Since he's trying to intercept key sequences for the purpose of signal
handling, it would be more portable to use the system's signal
handling facilities than attempting to manually interpret key
sequences as signals. The key sequences can vary from system to
system, but the signal types and method of handling are likely to be
more or less the same.

Also only few of the possible signals are mapped to keyboard
sequences. What if a signal is sent from another process, instead of
the user? Inspite of all this, some signals like SIGKILL can't be
ignored.

If the OP's shell's response to signals is not canonical for the
concerned platform, then potential users are likely to get annoyed
with his programme.

[GMM50]

Re: keyboard input intercept

On Mar 2, 12:13 pm, RJ45 <r...@NOSPAMsla cknet.comwrote:

Hello,
I am writing a shell in C.
I need to intercept Signals like CTRL+C or CTRL+D
and set to ignore them. This is on Unix, using gcc.
my goal is to avoid users escaping the shell with SIGINT
SIGQUIT signals using keyboard input.
Anyone could give me a little hint ?
>
thanks
>
Rick

If you are working on a PC, those key sequences are interperated in
the keyboard handler most likely a dll.
I've done some easy rewrites to just see if a key was pressed. Turbo
C 3.x had Kbhit() function that reported if a key was hit.

I suspect WinXP and beyond have further removed you from the hardware.

gm

[santosh]

Re: keyboard input intercept

GMM50 wrote:

On Mar 2, 12:13 pm, RJ45 <r...@NOSPAMsla cknet.comwrote:

Hello,
I am writing a shell in C.
I need to intercept Signals like CTRL+C or CTRL+D
and set to ignore them. This is on Unix, using gcc.
my goal is to avoid users escaping the shell with SIGINT
SIGQUIT signals using keyboard input.
Anyone could give me a little hint ?

thanks

Rick

>
If you are working on a PC, those key sequences are interperated in
the keyboard handler most likely a dll.

Key sequences have nothing to do with signals. The fact that a few
keys are mapped to some common signals doesn't mean a program has to
mess around with the raw keyboard input to handle signals.

I've done some easy rewrites to just see if a key was pressed. Turbo
C 3.x had Kbhit() function that reported if a key was hit.

Proper signal handling must also take into account signals received
from other processes.

I suspect WinXP and beyond have further removed you from the hardware.

There's no need to do keyboard handling to implement response to
signals, not for an ordinary application anyway.

[Keith Thompson]

Re: keyboard input intercept

"santosh" <santosh.k83@gm ail.comwrites:

GMM50 wrote:

>On Mar 2, 12:13 pm, RJ45 <r...@NOSPAMsla cknet.comwrote:

Hello,
I am writing a shell in C.
I need to intercept Signals like CTRL+C or CTRL+D
and set to ignore them. This is on Unix, using gcc.
my goal is to avoid users escaping the shell with SIGINT
SIGQUIT signals using keyboard input.
Anyone could give me a little hint ?

>>
>If you are working on a PC, those key sequences are interperated in
>the keyboard handler most likely a dll.

I think you mean if you're working under MS Windows (PCs can, and
often do, run other operating systems). The OP specifically said he's
using Unix, which doesn't have DLLs (at least not by that name).

Key sequences have nothing to do with signals. The fact that a few
keys are mapped to some common signals doesn't mean a program has to
mess around with the raw keyboard input to handle signals.

<OT>
On Unix-like systems, if a program doesn't perform any system-specific
actions, then typing Control-C will most likely cause a SIGINT signal
to be delivered to the current program.

The OP can either (a) use signal() (or some system-specific function
like sigaction()) to set up a handler for the signal, or (b) do some
system-specific stuff to reconfigure the system so that Control-C is
treated as an ordinary character.

The signal-handling method is probably simplest, since it leaves it up
to the OS (and the user's settings) to determine which characters send
which signals.
</OT>

The details are, of course, system-specific; I suggest asking in a
comp.unix.progr ammer -- but check <http://www.faqs.org/faqs/unix-faq/>
first.

--
Keith Thompson (The_Other_Keit h) kst-u@mib.org <http://www.ghoti.net/~kst>
San Diego Supercomputer Center <* <http://users.sdsc.edu/~kst>
"We must do something. This is something. Therefore, we must do this."
-- Antony Jay and Jonathan Lynn, "Yes Minister"