These are the first two results when I search "fork vs exec" in google.
http://www.yolinux.com/TUTORIALS/ForkExecProcesses.html http://en.wikipedia.org/wiki/Fork-exec I found very good explanations in both the links(yolinux is a bit better) -Sri On Tue, Feb 7, 2012 at 12:38 AM, Vijay Chauhan <[email protected]>wrote: > Hi List, > > I am learning Linux and trying to understand exec and fork function. > execl says that it overlays the running address space. What does it mean? > > I created the following program and used top command with > intentionally wrong arguments: > > #include<stdio.h> > #include<unistd.h> > #include<sys/types.h> > #include<stdlib.h> > > int main(){ > int a = -1; > if(fork()==0){ > printf("Inside child\n"); > printf("child pid=%d, parentid=%d\n", getpid(), getppid()); > execl("/usr/bin/top", "/usr/bin/top", ">/dev/null" > ,(char*)0 ); > scanf("inside child provide a %d", &a); > printf("Inside child a=%d\n", a); > exit(1); > } else { > printf("Inside parent, going to wait\n"); > printf("my pid=%d, parentid=%d\n", getpid(), getppid()); > scanf("input parent %d\n", &a); > wait(NULL); > printf("Wait over\n"); > printf("Inside parent a=%d\n", a); > } > return 0; > } > > When i run this program, it gives following output: > [vijay@localhost]$ ./a.out > Inside parent, going to wait > Inside child > child pid=2775, parentid=2774 > my pid=2774, parentid=2681 > top: unknown argument '>' > usage: top -hv | -bcisSHM -d delay -n iterations [-u user | -U user] > -p pid [,pid ...] > > 10 > Wait over > Inside parent a=-1 > [vijay@localhost]$ > > Why the child scanf and printf not executed? > In the parent program, i expected input parent should be printed. But > it doesnt and just wait for some input. When i entered 10 it resumes > but printing -1 as a value. > > Could anyone please help me to understand this behavior? or any good > tutorial or book > > Thanks. > Vijay > > _______________________________________________ > Kernelnewbies mailing list > [email protected] > http://lists.kernelnewbies.org/mailman/listinfo/kernelnewbies > -- SK Malik
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