Question

The aim of the program is to fork a new child process and execute a process which also has command line arguments. If I enter /bin/ls --help, I get the error:

shadyabhi@shadyabhi-desktop:~/lab/200801076_lab3$ ./a.out
Enter the name of the executable(with full path)/bin/ls --help
Starting the executable as a new child process...
Binary file to be executed: /bin/ls
/bin/ls: unrecognized option '--help
'
Try `/bin/ls --help' for more information.
Status returned by Child process: 2
shadyabhi@shadyabhi-desktop:~/lab/200801076_lab3$

What would be the right argument to execve()?

#include<stdio.h>
#include<string.h>      //strcpy() used
#include<malloc.h>      //malloc() used
#include<unistd.h>      //fork() used
#include<stdlib.h>      //exit() function used
#include<sys/wait.h>    //waitpid() used

int main(int argc, char **argv)
{
    char command[256];
    char **args=NULL;
    char *arg;
    int count=0;
    char *binary;
    pid_t pid;
    printf("Enter the name of the executable(with full path)");
    fgets(command,256,stdin);
    binary=strtok(command," ");
    args=malloc(sizeof(char*)*10);
    args[0]=malloc(strlen(binary)+1);
    strcpy(args[0],binary);
    while ((arg=strtok(NULL," "))!=NULL)
    {
        if ( count%10 == 0) args=realloc(args,sizeof(char*)*10);
        count++;
        args[count]=malloc(strlen(arg));
        strcpy(args[count],arg);
    }
    args[++count]=NULL;
    if ((pid = fork()) == -1)
    {
        perror("Error forking...\n");
        exit(1);
    }
    if (pid == 0)
    {
        printf("Starting the executable as a new child process...\n");
        printf("Binary file to be executed: %s\n",binary);
        execve(args[0],args,NULL);
    }
    else
    {
        int status;
        waitpid(-1, &status, 0);
        printf("Status returned by Child process: %d\n",WEXITSTATUS(status));
    }
    return 0;
}

Answer 1

The first entry in the args array should be the program name again. Your code calls /bin/ls with --help as the process name.