#include <stdio.h>
#include <sys/types.h>
#include <unistd.h>

main()
{
    char buf[1024];
    char *args[64];

    for (;;) {
        printf("Command: ");

        if (gets(buf) == NULL) {
            printf("\n");
            exit(0);
        }

        /*
         * Split the string into arguments.
         */
        parse(buf, args);

        /*
         * Execute the command.
         */
        execute(args);
    }
}

/*
 * parse--split the command in buf into
 *         individual arguments.
 */
parse(buf, args)
char *buf;
char **args;
{
    while (*buf != NULL) {
        /*
         * Strip whitespace.  Use nulls, so
         * that the previous argument is terminated
         * automatically.
         */
        while ((*buf == ' ') || (*buf == '\t'))
            *buf++ = NULL;

        /*
         * Save the argument.
         */
        *args++ = buf;

        /*
         * Skip over the argument.
         */
        while ((*buf != NULL) && (*buf != ' ') && (*buf != '\t'))
            buf++;
    }

    *args = NULL;
}

/*
 * execute--spawn a child process and execute
 *           the program.
 */
execute(args)
char **args;
{
    int pid, status;

    /*
     * Get a child process.
     */
    if ((pid = fork()) < 0) {
        perror("fork");
        exit(1);
    }

    /*
     * The child executes the code inside the if.
     */
    if (pid == 0) {
        execvp(*args, args);
        perror(*args);
        exit(1);

}

    }
    /*
     * The parent executes the wait.
     */
    while (wait(&status) != pid)
        /* empty */ ;

void execute(char **args)
{
    /* 
     * maybe some extra variables to hold argument lists for
     * parent and child calling execvp.
     * I just called them args1 and args2 below. Of course
     * it is possible just to rearrange args to be able to use
     * it without having new stuff here, and that's how I
     * might do it.
     */
    pid_t cpid;

    cpid = fork();

    switch (cpid) {
    case -1:
        perror("fork");
        break;

    case 0:
        printf("This is the child process\n");
        printargs(args);
        /* do whatever the child is supposed to do with args.
         * that is: create an argument list for execvp that
         * has the first shell command from args
         */

        /*execvp(*args1, args1); */ /* args1 feeds first shell command to execvp */
        /*perror(*args1); */
        exit(1);

    default:
        printf("This is the parent process\n");
        printargs(args);
        /* do whatever the parent is supposed to do with args.
         * that is: create an argument list for execvp that
         * has the second shell command from args
         */

        /*execvp(*args2, args2); */
        /*perror(*args2); */
        exit(1);
    }
}

void printargs(char **args)
{
    int i = 0;
    while (args[i]) {
        printf("args[%d]: <%s>\n", i, args[i]);
        i++;
    }
}