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
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