C programming basic shell

Question

I am trying to write a simple shell which accepts command line input and execute it as a background task.

How do I allow the child process to report to the parent process once it is completed, like the Bash shell?

user@user-desktop:~$ sleep 10 &
[1] 3729
user@user-desktop:~$ sleep 2 &
[2] 3730
user@user-desktop:~$ 
[1]-  Done                    sleep 10
[2]+  Done                    sleep 2

J-16 SDiZ · Accepted Answer · 2011-10-16 10:50:58Z

3

Since this is your homework, I won't give you full answer.

The GNU Glibc manual list the requirnment for job control shell. Let's see if you can understand it.

Basically:

you have to change the control terminal to make jobs run in background
you have to handle SIGCHLD (or wait) to monitor jobs

Ask again after you have read it.

edited Oct 16, 2011 at 10:50

answered Oct 16, 2011 at 10:45

J-16 SDiZ

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2 Comments

ilovetolearn Over a year ago

hi, I have read gnu.org/software/libc/manual/html_node/…. But I still don't have any idea in implementing the control terminal you are mentioning. Can you elaborate further?

J-16 SDiZ Over a year ago

@liangtech, click the "next" link. It's the "tcsetpgrp" in 27.6.4 Foreground and Background

ktf · Accepted Answer · 2011-10-16 10:48:28Z

0

You need to code a signal handler that handles the SIGCHLD (sometimes named SIGCLD) signal which is sent to parent processes when a child terminates.

answered Oct 16, 2011 at 10:48

ktf

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6 Comments

cnicutar Over a year ago

And do what in the signal handler ?

ilovetolearn Over a year ago

I understand I can implement a signal handler to "listen" for SIGCHLD when the child process terminates it will send a SIGCHLD signal. But what is the [2]+ beside the command [2]+ Done sleep 2

ktf Over a year ago

@liangteh: The "done" message is not written by the child - it's the parent process (the shell) that writes out that one of the child processes has terminated. ---

ilovetolearn Over a year ago

@ktf how about [1] and [2] what are they suppose to represent?

Chris Over a year ago

@liangteh Its the job number. all processes that run in the background of a shell are numbered. with the command 'fg 1' you can get the job 1 to the foreground again.

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