/*
 * Assignment Three
 *
 * Write a program to prompt for a second program name
 * with optional arguments. Then execute the program
 * from a child of your program.
 *
 * Use the script program to show the program source code,
 * its compilation, and run time behavior.  Show success
 * and failure of executing the command argument.
 *
 * Here is a test program that forks and executes the ls
 * program.  Begin by testing it to see if it works.
 */
#include <stdio.h>  /* Defines printf() and other fxxxxx() I/O services */
#include <stdlib.h> /* Defines exit() and other library support routines */
#include <unistd.h> /* Defines exec() family of services */

char command[255];

main (int argc, char *argv[], char *envp[]) {
   register char **p;
   int pid, status;

   char *arg="-ls";
   char *dir="/bin";
   char *prog="/bin/ls";

   for (p = argv; *p ; p++) {
     printf ("%s\n", *p);
   }
   if (fork() == 0) { /* Child code */
   gets (command); /* Gcc will complain - ignore */
   if (execl (prog, prog, arg, dir, 0))
     /* -1 return means error */
     printf ("Cannot find file\n");
     exit(222);
   } else { /* Parent code */
   pid = wait (&status);
   printf ("Statushigh = %d, Statuslow = %d, PID = %d\n", ((status & 0xff00) >> 8), (status & 0xff), pid);
   }
}
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/*
 * This second example prompts the user and reads the typed string
 * into a buffer. String conditioning assumes the ls command.
 * You have to make it more general for all commands.
 */
#include <stdio.h>  /* Defines printf() and other fxxxxx() I/O services */
#include <stdlib.h> /* Defines exit() and other library support routines */
#include <unistd.h> /* Defines exec() family of services */

char command[255];

main (int argc, char *argv[], char *envp[]) {
 register char **p;
 int pid, status;

 for (p = argv; *p ; p++) {
    printf ("%s\n", *p);
 }
 if (!fork()) { /* Child code */
   printf ("Yes master?\n");
   gets (command);
   printf ("%s\n", command);
   /* Assume /bin/ls -l was typed */
   command[7] = 0;
   command[13] = 0;
   if (execl (command, command, &command[8], 0))
     /* -1 return means error */
     printf ("Cannot find file\n");
     exit(123);
   } else { /* Parent code */
   pid = wait (&status);
   printf ("Statushigh = %d, Statuslow = %d, PID = %d\n",
     ((status & 0xff00) >> 8), (status & 0xff), pid);
   }
}
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/*
 * A string processing sample is shown in this third example.
 */
#include <stdio.h>  /* Defines printf() and other fxxxxx() I/O services */
#include <stdlib.h> /* Defines exit() and other library support routines */
#include <unistd.h> /* Defines exec() family of services */
#include <ctype.h>  /* Defines isxxxx() family of services */
#include <string.h> /* Defines strxxx() family of services */

#define TRUE  1
#define FALSE 0
#define NULL  '\0'

char command[255];

main (int argc, char *argv[], char *envp[]) {
 register char **p;

 int count, pid, status;
 char *cp, *prog, *cmdptr, *arg1;

 if (fork() == FALSE) {         // Child code - Concise version: if (!fork())
   printf ("Yes master?\n");
   // If fgets() reads in the newline and stores it into the buffer.
   // Also, null ('\0') character is placed after the last character in the buffer.
   count = strlen(command);
   printf ("String Length: %d\n", count);
   cp = command;                // Initialize working pointer
   prog = cp;                   // Assume 1st char in command buffer is program name
   while (!isspace(*cp)) cp++;  // Skip over program name until white space found
   if (*cp == '\n') goto error; // Reached end of string too soon, no argument
   *cp++ = NULL;                // Terminate string and skip to next char in string
   printf ("ProgName: %s\n", prog);
   while (isspace(*cp)) cp++;   // Skip white space at beginning of 1st argument
   arg1 = cp;                   // Save pointer to start of 1st argument
   while (!isspace(*cp)) cp++;  // Skip over 1st argument until white space found
   *cp = NULL;                  // Null terminates string for C library routines
   printf ("Arg1: %s\n", arg1);
   // A loop is needed here to capture all arguments until end of command buffer found.
   // See "man strtok" for another (easier) way of doing string processing.
   printf ("Reached end of string\n");
   printf ("Ready to exec\n");
   fflush(stdout);
   if (execl (prog, prog, arg1, 0)) {
     /* -1 return means error */
     printf ("Exec service failed\n");
     fflush(stdout);
error:
     printf ("Cannot find file\n");
     fflush(stdout);
     exit(123);
     } // End if (exec)
   } else {                      // Parent code
   pid = wait (&status);
   printf ("Statushigh = %d, Statuslow = %d, PID = %d\n",
     ((status & 0xff00) >> 8), (status & 0xff), pid);
   }
}

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