topic How do I ignore Ctrl-C in ksh scripts? in Operating System - HP-UX

How do I ignore Ctrl-C in ksh scripts?

Stuart Abramson_2 — Mon, 16 Feb 2004 11:32:00 GMT

I showed the DBAs how to run our basic BCV unmount/synch/split/mount scripts.

Today, not for the first time, one of the DBAs "Ctrl-C"-d out of one of the BCV scripts, thus leaving the BCV in an "inconsistent" state - half-way unmounted and halfway still mounted (if you follow my meaning).

How so I modify a ksh script to IGNORE Ctrl-C? I don't want to "trap" it. I just want to ignore it, and keep right on going from where it is.

Re: How do I ignore Ctrl-C in ksh scripts?

A. Clay Stephenson — Mon, 16 Feb 2004 11:41:34 GMT

I assume that Ctrl-C triggers a SIGINT. Confirm this via stty -a and look for the value associated with "intr".

You can now cause a SININT to be ignored via the trap statement using a null string command argument.

trap '' 2

Plan B. Use stty to set intr to an impossible value:
stty intr 0377
but be sure to reset to original value later because a stty command applies to the terminal device rather than a process.

Re: How do I ignore Ctrl-C in ksh scripts?

Stuart Abramson_2 — Mon, 16 Feb 2004 13:43:33 GMT

Clay:

That looks absolutely right to me. I'll give it a try and post points.

Stuart

Re: How do I ignore Ctrl-C in ksh scripts?

Bill Hassell — Mon, 16 Feb 2004 14:00:28 GMT

You probably want to trap all the common interrupts and ignore them. The HP-UX standard /etc/profile does this. Do it this way:

trap "" 1 2 3

or

trap "" HUP INT QUIT

This will do nothing for CTRL-C, as well as a hang-up (connection break, either modem or network) or kill -3 to create a core dump.

Re: How do I ignore Ctrl-C in ksh scripts?

Stuart Abramson_2 — Mon, 16 Feb 2004 14:23:33 GMT

If I do a "stty -a" I get this:

# stty -a

...
intr = ^C; quit = ^\; erase = ^H; kill = ^U
eof = ^D; eol = ^@; eol2 = ^@; swtch = ^@
stop = ^S; start = ^Q; susp = ^Z; dsusp = ^@
werase = ^@; lnext = ^@
...

Does this mean that?:
...SIGINT is ^C
...SIGQUIT is ^\
...SIGKILL is ^U

Re: How do I ignore Ctrl-C in ksh scripts?

Mark Grant — Mon, 16 Feb 2004 14:27:56 GMT

Certainly does Stuart. I personally would avoid changing this just to stop people breaking out of an application. It can cause too many headaches should the application fall over sometime or things like that.

I would go with "trap" myself. Have used it many times and it will do the trick for you.

Re: How do I ignore Ctrl-C in ksh scripts?

A. Clay Stephenson — Mon, 16 Feb 2004 14:28:24 GMT

Yes, although in stty the '^' (caret) indicates Control so that ^C ---> Control-C.

Re: How do I ignore Ctrl-C in ksh scripts?

Stuart Abramson_2 — Mon, 16 Feb 2004 14:31:26 GMT

Why don't I see "SIGHUP" and "SIGTERM" in my "stty -a"?

Re: How do I ignore Ctrl-C in ksh scripts?

Mark Grant — Mon, 16 Feb 2004 14:36:59 GMT

You can't send those from a keyboard. If you want a list of other things you can't send, try "kill -l" (that a lower case L just to make it clear)

Re: How do I ignore Ctrl-C in ksh scripts?

A. Clay Stephenson — Mon, 16 Feb 2004 14:38:38 GMT

Because those signals are not associated with keystrokes. SIGHUP is the 'hangup' signal. Think of "hanging up" the modem -- or powering off the terminal -- there is, of course, no key to press on a terminal if you've done gone and turned the danged rascal off. Similarly, SIGTERM is a system-generated (software) signal most commonly invoked from the shell with a kill -15 PID; there ain't no key associated with it neither.

Re: How do I ignore Ctrl-C in ksh scripts?

Stuart Abramson_2 — Mon, 16 Feb 2004 14:40:31 GMT

Worked perfectly. Thanks all.

Stuart