Stimulate a simple Shell in C

1. Shell operation

LSH is a simple implementation of a shell in C. It demonstrates the basics of how a shell works. The basic operation of a shell is based on three main thing:

• Initialize: In this step, a typical shell would read and execute its configuration files. These change aspects of the shell's behavior.

• Interpret: Next, the shell reads commands from stdin and executes them

• Terminate: After its command are executed, the shell executes any shutdown command, frees up any memory, and terminates

Therefore, a simple way to handle commands is with three steps:

char *lsh_read_command(void);	    /* Read: Read the command from standard input*/		
char **lsh_parse_command(char *);   /* Parse: Separate the command string into arguments*/
int lsh_execute(char **);           /* Execute: Run the parsed command */

These functions are put into the main function:

int main(int argc, char *argv[])
{
  char * cmd, **tokens;
  int status;
  do {
    printf("MY SHELL > ");
    fflush (stdout);
    cmd = lsh_read_command();
    tokens = lsh_parse_command(cmd);
    status = lsh_execute(tokens);
  } while(status !=0);

  exit(EXIT_SUCCESS);
}

Shell management

The commands of shell are managed by array of string builtin_str and function pointer builtin_func. If you want to contribute and improve or add command the shell, just add name the command in builtin_str, and implemented function in builtin_func function pointer. I just simply implement 4 basic operation including:

1. help: Provide information all commands are implemented
2. exit: exit the Shell
3. pwd: get current directory.
4. cd: changes directory

/*
  List total commands in Shell
*/
char *builtin_str[] = {
  "help",
  "exit",
  "pwd",
  "cd"
};

/*
  Function pointer used for pointing to function of implemented command
*/

int (*builtin_func[]) (char **) =
{
  &lsh_help,
  &lsh_exit,
  &lsh_pwd,
  &lsh_cd
};

Shell Script

Reference:

https://www.shellscript.sh/index.html