asked on

exec() for Linux

Well I tried the following code:-

#include <stdio.h>
int main ( ) {
int i;
printf("Before calling execl()\n");
i = execl("/bin/sh","sh","shpg.sh",NULL);
if(i<0) {
perror("execl()");
exit(0);
}
printf("After calling execl()\n");
return 0;
}

My shpg.sh is:-

echo "Some Text"

I expect the output to be:-

Before calling execl()
Some Text
After calling execl()

But the output is:-

Before calling execl()
Some Text

Can somebody tell me why the code after the exec is not being executed? Thanks in advance.

ASKER CERTIFIED SOLUTION

grue

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grue

Err, instead of just directly looking at the content of waitpid's status (as I did in my example), there are some macros you should be using... Something like:

WEXITSTATUS(i);

but I think it happens to "work" in this case because you're just looking for a zero result and the program you run doesn't generate any signals or anything funky like that... but you really shouldn't be looking at the value directly; use the macro.

see the man page for waitpid for more details.

pankajtiwary

ASKER

Thanx Grue,
I appreciate your help in clarifying my confusion. Yeah, You got exactly what I wanted. I got your point. Actually I was thinking when completing the request execl returns and the rest of the code executes. But it's not like that. I case of success execl() never returns. Thanx again.