topic trap question in Operating System - HP-UX

trap question

kamal_15 — Thu, 13 Jan 2005 04:30:58 GMT

I want to know what is the (trap).

i read about it .but i coudn't use it
can any one help me?

i want an example

Re: trap question

Michael Schulte zur Sur — Thu, 13 Jan 2005 04:35:25 GMT

Hi,

trap is a shell command to ignore certain signals like ^C or hangup. See the manual page of the shell you are using. It is used like
trap 1 2 15 ""
You specify the signals you want to catch and the action that is to be taken when a signal occurs.

greetings,

Michael

Re: trap question

kamal_15 — Thu, 13 Jan 2005 04:48:03 GMT

thank u man

but i don't understand how can i receive the
output from trap?

EX:
****
if i want to execute a sample shell
and i want to receive a signals explane the status.

what command can i write to do that

NOTE:
i have hp-ux V.10
when i type
man trap
no manual entry

thanx

Re: trap question

Stephen Keane — Thu, 13 Jan 2005 04:50:13 GMT

man trap wont show anything because trap is part of the shell. Try man ksh instead and look for trap

e.g.

trap 15 "echo \"Hello\""

Re: trap question

Stephen Keane — Thu, 13 Jan 2005 04:53:05 GMT

If you do
# kill -l
it will show you the names of the signals and their numeric values. e.g.

15 = TERM or SIGTERM

Re: trap question

Michael Selvesteen_2 — Thu, 13 Jan 2005 06:36:09 GMT

Trap is an interrupt signal (CTRL-C) usually kills the process.

Processes may be sent signals using either the kill command, or a control key combination such as CTRL-C.

The trap command typically appears as one of the first lines in the shell script. It contains the commands to be executed when a signal is detected as well as what signals to trap.

#!/bin/sh
TMPFILE=/usr/tmp/junk.$$
trap 'rm -f $TMPFILE; exit 0' 1 2 15
.
.
.

Upon receiving signals 1, 2 or 15, $TMPFILE would be deleted and the script would terminate the shell script normally. This shows how trap may be used to clean up before exiting.

#!/bin/sh
TMPFILE=/usr/tmp/junk.$$
trap '' 0 1 2
.
.
.

The above example shows how trap may be used to ignore specific signals (0, 1 and 2).

NOTE that when the signal is received, the command currently being executed is interrupted, and execution flow continues at the next line of the script.

Hope this helps

--
M

Re: trap question

Gerhard Roets — Fri, 14 Jan 2005 03:21:30 GMT

Hi Kamal

For future reference.

The command "man sh-posix" would be a good place to look for infomation regarding built in shell commands.

Regards
Gerhard