Re: fork: why to copy process to run new program?

[Glynn Clements <glynn@gclements.plus.com>]

Tom wrote:

> >>         Why, when a program needs to open another, have fork to copy all
> >>         the
> >> initial program just for 'exec' the another? Could'nt initial program
> >> just to "tell" the kernel for open the second program?
> > 
> > I'm not sure what you're getting at.
> > 
> > If you're asking why fork() and exec() can't be combined into a single
> > spawn() primitive, the answer is twofold:
> 
> sorry by not clear explanation of my question in prev article.
> but I think your answer help to kill my doubt (I say "help" cause I have to
> understand more the whole thing before, maybe reading some docs).
> 
> but my question could be done so: couldn't processA (example.. bash), when
> wants to run processB (example.. ls), just "tell" the kernel (using some
> system call, sure) "hey, please, open /bin/ls. Oh, do you need some env
> vars? ok, here is the list, PWD=/home/tom, VAR2=VALUE2, etc.. Oh do you
> want to know about file descriptos? ok, here is...".

Well, that's essentially what exec() does, but exec() runs the
specified program *in* place of whichever program called exec().

If you want to run a specified program without terminating the current
program, you have to fork() a new process and have the new process run
the program.

-- 
Glynn Clements <glynn@gclements.plus.com>