how to pass command line arguments to a child process after fork()

Question

I have the following code draft.

#include <fcntl.h>
#include <stdio.h>
#include <unistd.h>
#include <stdlib.h>    

int main(int argc, char *argv[])
{

    printf( "usage: %i filename", argc );

    pid_t pID = fork();
    if (pID == 0)                // child
    {
        // Code only executed by child process
        printf("Child PID: %i", pID);

        int file = open("/tmp/rtail", O_CREAT | O_WRONLY);

        //Now we redirect standard output to the file using dup2
        dup2(file,1);

        char tmp[30];
        sprintf(tmp, "cat `tail -f %s`", argv[1]);
    }
    else if (pID < 0)            // failed to fork
    {
        printf("Failed to fork");
        exit(1);
        // Throw exception
    }
    else                                   // parent
    {

    }

    // Code executed by both parent and child.  

    return 0;
}

How do I pass command line arguments to a child process? For example, running ./app alch.txt I want

sprintf(tmp, "cat `tail -f %s`", argv[1]);

to produce

cat `tail -f alch.txt`

in tmp.

Answer 1

How do I pass command line arguments to a child process?

You don't need to do anything special; fork ensures that each process gets all local variables, including argv.

Answer 2

Sorry for the trouble, it indeed works fine. My earlier version didn't work for some reason, but apparently I've changed something to make it right. Will run my code before a question next time.