Okay -- but I still don't get why the message isn't displayed. Other folks can get it. Any idea why not me? My book says it should display the message and go right back to the loop.
Sorry if it's a basic question, but I'm still new to this.
Okay -- but I still don't get why the message isn't displayed. Other folks can get it.
No they don't, not when their shell's not the foreground process.
Quote:
Any idea why not me?
When you're running an external command, your shell isn't the foreground process, so the signal doesn't get delivered to it. It gets delivered to the foreground process instead, in this case, sleep, which causes it to quit and return a non-zero error code:
This is because the process isn't actually killed by the shell -- it's killed directly, by you. The terminal device translates control-C directly into SIGINT for you. What the 'foreground process' is isn't a property of the shell, either -- it's a property of the terminal itself, so it always knows where to send SIGINT direct.
Quote:
My book says it should display the message and go right back to the loop.
This is true only if your shell is the foreground process. If it's in the middle of running any externals, your shell's not in the foreground.
Last edited by Corona688; 07-06-2011 at 09:10 PM..
I'm sorry to be so dense corona, but can you tell me what is meant by external command, foreground process, etc. I'm not sure the book is clear on this.
I'm sorry to be so dense corona, but can you tell me what is meant by external command, foreground process, etc. I'm not sure the book is clear on this.
An external command is one that's not built into the shell. It exists as an actual file somewhere, and when you run it, it creates a whole new process.
builtins, on the other hand, are commands the shell just automatically knows how to do. There's no 'read' program on the system, but 'read' works anyway, putting the qwertyuiop typed on the keyboard into the variable VAR.
So when you run an external command, it's run seperately, and it has control of the terminal until it's done. When you run an internal command, no programs are run, the shell just does what you tell it internally.
Another important builtin is one you probably already know -- 'cd'. Consider how external programs are run -- they have a separate process, their own environment. If cd wasn't a builtin it couldn't possibly work, because it'd create a new process, change that process' directory, quit, and return to your shell, leaving your shell unchanged.
Hi Folks -
For some reason, my trap command is not working. It's placed just prior to a normal exit:
#:: ------------------------------------------------------------------------
#::-- Script Name: LCM_Backup.sh
#::
#::-- Description: This script leverages Utility.sh to perform LCM... (16 Replies)
Use and complete the template provided. The entire template must be completed. If you don't, your post may be deleted!
1. The problem statement, all variables and given/known data:
That is the last reply I received from my instructor, and I'm looking for some alternatives.
When using... (2 Replies)
dear all;
I can't under stand what does "trap" command do:
for example see below:
trap "echo; echo no interrupts >&2; sleep 3" 2 3 15
Plz , can any body explain the action of this command?
BR (3 Replies)
Hello experts!
I need to know the use of trap command please
In one of our program we have trap "rm -f temp1 ; exit 1" 1 2 15 0
and program always exit with 1
there is a rm -f temp1 as well at the end of the program
as
rm -f temp1
exit 0
when I test a probram with set... (4 Replies)
Hi folks,
I have tried to add some trap detection in the below script....this script is used to monitor database activities...in a rather awkward way :rolleyes:....
The idea behind adding trap is that....this script creates lots of temporary files in the running folder to store the count... (1 Reply)
Hi,
I would like to know the use of TRAP command. I am very new to the UNIX environment. I have just started learning the basic. So please teach me in a very simple way to understand.
Also i would like to know the use of following command:
trap 'dialog --msgbox "Script Aborted1" 6 50 ;... (2 Replies)
Could anybody tell me what the trap command does and how it performs the action it does. I had read the trap manual page but it is too concise that nothing is clear about it. Please tell how it works. (1 Reply)
Dear All
could you please explain me what does the trap command do and how I can write a program which can work as a trap command(in C Language). (1 Reply)
i have the following script that displays the current time until the user presses CTR + c.... but it does not work properly....
Something is not right with the trap command...
Help plz... :confused:
# script to continuously display current time.
# if script is terminated trap signal... (3 Replies)
I'm using the trap command to capture any signals received whilst my script is running.
How's the best way of writing the signal and any other error messages to a file/error log' without having to type '2>$1' on the command line after the script name?
Cheers (3 Replies)