background processes

chameleon8636 · 10-15-2008, 04:27 PM

I am creating a dummy UNIX shell and am getting confused on creating a background process. When a line ends with a '&' then it starts the command before the '&' as a background process. I have it recognizing the '&' and forking a new process but I don't know how to actually run the command before the '&'. I know it is going to do with exec() but I do not know how to implement it.

Thanks

ArfaSmif · 10-15-2008, 06:05 PM

Hi chameleon8636,

I'm not sure exactly what you are trying to do. If you want to run a command in the background, all you have to do is append the ampersand (&) at the end of the line.

eg. ls -al &

will run ls -al in the background, but the output still goes to standard out, which is normally your terminal.

Can you be a bit more specific about exactly what you are trying to do and maybe I can give you some more pointers.

chameleon8636 · 10-15-2008, 06:14 PM

I am programming a UNIX shell in C++. I want to make it for when the user enters a '&' at the end of a line it runs the command they entered in the background. I do not know how to implement this in C++.

EDIT: Sorry, the command before the '&' will not be a simple command (i.e. cd, ls). I think that it will be just something that runs in the background until it gets terminated and then it outputs whatever it was running.

ArfaSmif · 10-15-2008, 06:18 PM

Sorry mate. I can do shell scripting but have no idea about C++ programming. Can't you find any examples on the net?

chameleon8636 · 10-15-2008, 06:25 PM

No i couldn't, that is why I am here asking?

chrism01 · 10-15-2008, 06:31 PM

try

man 3 exec

which describes the C manual exec cmd. Basically it replaces the 'current' program (your forked process) with a completely new program and runs that instead.
This also means that it will not return.
See also http://www.yolinux.com/TUTORIALS/ForkExecProcesses.html

ArfaSmif · 10-15-2008, 06:34 PM

I did a quick search on google and found this site "www.codeguru.com". Within this site I did a search for "fork" and "threads" - maybe these can be of help to you. :-) Good luck.