Question

Ubuntu, Linux, MacOS use one of these systems.
1a. Create a C program that forks a child process that executes the command ‘ls’.
1b. Extend the program you created in Problem 1a such that it takes an argument. For example, the created child process should be able to execute the command ‘ls’ with any arbitrary single argument such as ‘ls -l’, and ‘ls -a’.

Answer 1

//Program for 1a

1a.

//solution

#include <stdio.h>

#include<string.h>

#include<stdlib.h>

#include<sys/wait.h>

#include<sys/unistd.h>

int main()

{

char *command[3];

int pid,status;

//create child process by using system call fork()

pid=fork();

if(pid > 0) // parent process

{

//wait for child to finish executing ls

wait(&status);

exit(0);

}

else //child process , execute ls command

{

//buld command

command[0]=(char*)malloc(sizeof(char)*3);

strcpy(command[0],"ls");

command[1]=NULL;

printf("Child process executes ls command\n");

printf("#####Output of ls command#####\n");

//execute using system call execvp

execvp(*command,command);

}

}

===============================

//Output

 gcc mySh.c
 ./a.out
Child process executes ls command
#####Output of ls command#####
a.out main.sh mySh.c

========================================

//Program for 1b

1b.

//solution

#include <stdio.h>

#include<string.h>

#include<stdlib.h>

#include<sys/wait.h>

#include<sys/unistd.h>

//make program to take command line args

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

{

char *command[3];

int pid,status;

//if there is no otion given for ls command , print error message to user and exit

if(argc < 2)

{

printf("Usage: %s single_argument_to_ls_command\n",argv[0]);

exit(-1);

}

//create child process by using system call fork()

pid=fork();

if(pid > 0) // parent process

{

//wait for child to finish executing ls

wait(&status);

exit(0);

}

else //child process , execute ls command

{

//buld command

command[0]=(char*)malloc(sizeof(char)*3);

strcpy(command[0],"ls");

command[1]=(char*)malloc(sizeof(char)*3);

strcpy(command[1],argv[1]);

command[2]=NULL;

printf("Child process executes ls command with argument %s\n",argv[1]);

printf("#####Output of ls %s #####\n",argv[1]);

//execute using system call execvp

execvp(*command,command);

}

}

========================

//Output

 gcc mySh.c
 ./a.out
Usage: ./a.out single_argument_to_ls_command
 ./a.out -l
Child process executes ls command with argument -l
#####Output of ls -l #####
total 16
-rwxr-xr-x 1 runner runner 8352 Oct 11 08:25 a.out
-rw-r--r-- 1 runner runner 0 Oct 11 08:08 main.sh
-rw-r--r-- 1 runner runner 1042 Oct 11 08:25 mySh.c

//Output2

 gcc mySh.c
 ./a.out -a
Child process executes ls command with argument -a
#####Output of ls -a #####
. .bash_history .bashrc .profile main.sh
.. .bash_logout .go.sh a.out mySh.c