Question

Write a C program that implements a simple shell. The shell takes a user command as input and execute the command.

When a shell is started, it should take user command, execute it and display the output.

Answer 1

#include <stdio.h>
#include<string.h>
#include<stdlib.h>

int main()
{
char buff[100];
char *p;
char *args[10];
int count=0,pid,i;
  
printf("Enter command example =>ls -l \n: ");
  
fgets(buff,sizeof(buff),stdin);
//eliminate /n in buff
buff[strlen(buff)-1]='\0';
printf("Output of user command %s \n",buff);
//alocate memory for 10 array of strings
for(i = 0; i < 10; i++)
{
args[i] = (char*)malloc(20*sizeof(char));
}
//printf("%s\n",buff);
//now make a argument list and add to string array
p=strtok(buff," ");
//printf("%s\n",p);
strcpy(args[count++],p);
while(p!=NULL)
{
  
p = strtok(NULL," ");
if(p == NULL)
break;
//printf("in While %s\n",p);
strcpy(args[count++],p);
}
//after building list of commands , execute command using execvp , for that create child process
/*pid = fork();
if(pid == 0) //child process
{
execvp(args[0],args);
}
else //parent process
{
//wait for chidl to finish
wait(0);
printf("Finished executing user command %s \n",buff);
}*/
//print args
args[count]=NULL;
execvp(args[0],args);
return 0;
}

---------------------------------

//output1
Enter command example =>ls -l   
: ls
Output of user command ls   
a.out main.c   

//output2
Enter command example =>ls -l   
: ls -l   
Output of user command ls -l
total 16
-rwxrwxrwx 1 root root 8928 Oct 15 07:11 a.out
-rwxrwxrwx 1 root root 1615 Oct 15 07:11 main.c