using execvp to execute commands that I have in an array

Question

I have a commands array and I want to execute each command in this array but I couldn't seem to get it working so I have

childPid = fork();


for(int i =0;i < numOfCommands;i++)
{
    if(childPid == 0)
    {
        execvp(commands[i], argv);
        perror("exec failure");
            exit(1);
    }
    else 
    {
        wait(&child_status);
    }


}

What this does, is that it only executes the 1st command in my array but doesn't proceed any further, how would I continue ?

And what if i want the order for the commands to executed randomly and the results be intermixed so do I have to use fork then ?

Community · Accepted Answer · 2020-06-20 09:12:55Z

2

You need to use fork in any case, if you want to execute more than one program. From man exec: (emphasis added)

The exec() family of functions replaces the current process image with a new process image.

…

The exec() functions return only if an error has occurred.

By using fork, you create a new process with the same image, and you can replace the image in the child process by calling exec without affecting the parent process, which is then free to fork and exec as many times as it wants to.

Don't forget to wait for the child processes to terminate. Otherwise, when they die they will become zombies. There is a complete example in the wait manpage, linked above.

edited Jun 20, 2020 at 9:12

CommunityBot

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answered Jan 31, 2016 at 3:19

rici

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8 Comments

Pro Over a year ago

Can you give me a simple example of how to use fork, and then I Don't need the for loop to circle through my array then if I used the fork ??

rici Over a year ago

@pro: i just added a link to man wait (although you should have that on your machine) which includes a complete example. Of course, you still need the for loop.

Pro Over a year ago

Ok I edited my code, I am trying to follow this example provided here cs.ecu.edu/karl/4630/sum01/example1.html but the thing is , if we are in the parent process how would we wait until the child is done ! should I just use waitpid() which by default wait for the chidlren to terminate ??

rici Over a year ago

@pro: please don't edit your questions after they have been answered, particularly in ways which make the answer inappropriate. If you want to ask a different question, ask a different question.

Pro Over a year ago

I think my code, is good now because wait(&status) puts the parent to sleep until the child is done right ??

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