Question

Edit the code (shell.c) given to do the tasks asked! will rate for correct answer! Also, include a screen shot of the output and terminal window of each command you used. Read carefully to do this task please.

Task 1 (100 points) There are many variations of the exec system call that can be used to execute an executable file (program) Calling exec does not create a new process, it replaces the current process with the new process. If the exec command fails, then it returns -1. But if it succeeds it does not return because execution proceeds at the beginning of the program that was execut ed. We will consider some useful forms of exec commands. 1. execl: takes the path name of an executable as its first argument, the rest of the arguments are the command line arguments ending with a NULL. execl("/bin/ls", "1s", "-a", "-l", NULL) 2. execv: takes the path name of a binary executable as its first argument, and a NULL terminated array of arguments as its second argument. The first element can be the command or" ". static char* args("Is", "-a", "-1", NULL; execv("/bin/1s", args) 3. execlp: same as execl except that we don't have to give the full path name of the command execlp ( " ls " , " ls " , "-a" , "-I " , NUTIL) ; 4. execvp: Same as exexv except that we don't have to give the full path name of the command static char * args[ execvp ("ls" ] = {"ls", "-a", "-1", NULI.); , args);

shell.c code given below.

#include <stdio.h>
#include <unistd.h>
#include <stdlib.h>
#include <sys/wait.h>
#include <string.h>
int main()
{
        int PID;
        char lineGot[256];
        char *cmd;
        while (1){
                printf("cmd: ");
                fgets(lineGot, 256, stdin); // Get a string from user (includes \n)
                cmd = strtok(lineGot, "\n"); // Get the string without the \n
                if( strcmp(cmd, "e") == 0 ) // loop terminates when "e" is typed
                        exit (0);
                // creates a new process. Parent gets the child's process ID. Child gets 0.
                if ( (PID=fork()) > 0)
                {
                        wait(NULL);
                }
                else if (PID == 0) /* child process */
                {
                        execlp (cmd, cmd, NULL);
                        /* exec cannot return. If so do the following */
                        fprintf (stderr, "Cannot execute %s\n", cmd);
                        exit(1); /* exec failed */
                }
                else if ( PID == -1)
                {
                        fprintf (stderr, "Cannot create a new process\n");
                        exit (2);
                }
        }
}

Answer 1

The solution for the above question is given below with the screenshot of output.
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I have kept the logic simple and output as per the question.

I have update the program to use execvp and strtok .

If there is anything else do let me know in comments

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--------------- CODE TO COPY -----------------------------------------------------------------------

shell.c

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <sys/wait.h>
#include <unistd.h>

int main() {

        int PID;
        char lineGot[256];
        char *cmd;

        while (1) {

    // Array of pointers for arguments
    char *args[16] = {0};

                printf("cmd: ");
                fgets(lineGot, 256, stdin);  // Get a string from user (includes \n)

                cmd = strtok(lineGot, "\n"); // Get the string without the \n
                if (strcmp(cmd, "e") == 0)   // loop terminates when "e" is typed

                  exit(0);
                // creates a new process. Parent gets the child's process ID. Child gets
                // 0.

    int i = 0;
    // Returns first cmd 
    args[0] = strtok(lineGot, " ");
    args[1] = strtok(NULL, " ");
    args[2] = strtok(NULL, " ");

                if ((PID = fork()) > 0) {

                        wait(NULL);

                } else if (PID == 0) /* child process */
                {

                        execvp(cmd, args);
                        /* exec cannot return. If so do the following */
                        fprintf(stderr, "Cannot execute %s\n", cmd);
                        exit(1); /* exec failed */

                } else if (PID == -1) {

                        fprintf(stderr, "Cannot create a new process\n");
                        exit(2);

                }
        }
}

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Output :