Question

DO NOT COPY PASTE THE SOLUTION FROM ANOTHER QUESTION! IT IS NOT THE RIGHT ONE, ANSWER WILL BE REPORTED IF NOT A UNIQUE SOLUTION.

Write a C program called myshell.c, which, when compiled and run, will do what the shell does, namely, it executes in a loop (until user types exit on the keyboard),

prints a prompt on the screen, reads the command typed on the keyboard (terminated by \n),

creates a new process and lets the child execute the user’s command,

waits for the child to terminate and then goes back to beginning of the loop.

If the command typed is exit, then your program should terminate.

Print the total number of commands executed just before terminating your program.

Assume that each line represents one command only, no command will end with & (all commands will be attached commands, no background execution),

user will not type ^c or ^z, all commands are simple commands, etc

Answer 1

#include <stdio.h>

#include<string.h>

#include<stdlib.h>

#include<sys/wait.h>

#include<unistd.h>

int main()

{

char buff[100];

char *p;

char *args[10];

int count=0,pid,i;

int no_commands=0;

while(1)

{

printf("myShell>");

count=0;

fgets(buff,sizeof(buff),stdin);

//eliminate /n in buff

buff[strlen(buff)-1]='';

//printf("%s ",buff);

if(strcmp(buff,"exit") == 0)

{

printf("Number of commands executed: %d ",no_commands);

printf("Bye... ");

exit(0);

}

//alocate memory for 10 array of strings

for(i = 0; i < 10; i++)

{

args[i] = (char*)malloc(20*sizeof(char));

}

//now make a argument list and add to string array

p=strtok(buff," ");

strcpy(args[count++],p);

while(p!=NULL)

{

p = strtok(NULL," ");

if(p == NULL)

break;

strcpy(args[count++],p);

}

//after building list of commands , execute command using execvp , for that create child process

args[count]=NULL;

pid = fork();

if(strcmp(buff,"exit") == 0)

{

printf("Number of commands executed: %d ",no_commands);

exit(0);

}

if(pid == 0) //child process

{

//execvp(args[0],args);

execvp(args[0],args);

perror("ps error: ");

printf("After execvp failed ");

exit(0);

}

else //parent process

{

//wait for chidl to finish

wait(0);

//printf("Finished executing user command %s ",buff);

++no_commands;

if(strcmp(buff,"exit") == 0)

{

printf("Number of commands executed: %d ",no_commands);

exit(0);

}

buff[0]='';

count=0;

*args=NULL;

}

fflush(stdin);

}

return 0;

}

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

//output1

myShell>exit
Number of commands executed: 0
Bye...

//output2

myShell>ls -l
total 16
-rwxr-xr-x 1 runner runner 8832 Feb 19 05:28 main
-rw-r--r-- 1 runner runner 1986 Feb 19 05:28 main.c
myShell>date
Tue Feb 19 05:28:46 UTC 2019
myShell>wc -l main.c
81 main.c
myShell>ps -eaf
UID PID PPID C STIME TTY TIME CMD
runner 1 0 0 05:20 ? 00:00:00 /dev/init -- /bin/init
runner 6 1 0 05:20 ? 00:00:00 /bin/init
runner 14 6 0 05:20 ? 00:00:02 cquery --init={"progressReportFr
runner 355 6 0 05:28 pts/0 00:00:00 ./main
runner 359 355 0 05:28 pts/0 00:00:00 ps -eaf
myShell>exit
Number of commands executed: 4
Bye...

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

//screenshot