C in a Unix environment Shell Program - Write, compile, and run a C program for

Question

C in a Unix environment

Shell Program - Write, compile, and run a C program for a custom-shell.

Part 1: Your shell will do the following, using system( ) to handle each command

   1. Command prompt (for example, #, ##, %, %%, or of your choice).
   2. Command “exit” or “quit” will exit (to terminate the program).
   3. Command “list” will do what ls command does (using system)

Part 2: Command Parsing (and print its components) using system() Your shell should be able to parse the command from user

   1. One command with arguments and options.
   2. Two commands with 1 pipe.
   3. Two commands with semicolon. For example, ls ; date
   4. One command with IO redirection symbol (<, >, >>)

Part 3: Handle pipe (using fork, pipe, dup2, exec) with two commands.

   Given a command from user, it forks a child process to execute the command while parent waits. When it is done, parent process wakes up and prints prompt for next command.

   Syntax: command | command
   Test line: ls -sF | grep /
   Man pages: pipe, dup2.

Part 4: Handle background execution of command with "&" and a sequence commands with ";".

   Test line: sleep 10 &
   Test line: sleep 10; ls &

Part 5: Signal processing (to handle Cntl+Z when command prompts) - SIGTSTP.

   Terminate the shell by exit command "exit" or Z (^Z)
   When a child process is running and the parent-process is waiting,
   Cntl+Z will be handled by the parent’s signal handler to kill the child process.

   Test Case: sleep 100 (and then press Cntl+Z) to kill the child process in sleep by the parent process.

   And ps command to see whether the child process is killed (gone).

Part 6: Handle multiple commands connected with pipe.

   For example, ls | grep ".c" | sort | tee list.txt | wc –l ; cat list.txt

Explanation / Answer

#include<stdio.h>

int main(){
    char ch[50];
    strcpy(ch,"");
    while((strcmp(ch,"exit")!=0)&&(strcmp(ch,"quit")!=0)){
        printf(" # ");
        scanf("%s",&ch);
        if(strcmp(ch,"list")==0){
            system("dir");
        }else{
            system(ch);
        }
    }
}

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