Nipunnyka / tiniShell

Basic Linux shell written in C using system calls with support for all bash commands with appropriate flags, piping, foreground and background processing

tiniShell

• Basic Linux shell written in C using system calls with support for all bash commands with appropriate flags, piping,foreground and background processing
• Multiple processes are supported using multithreading

Note: no support for regex yet

Installing tiniShell

1. Run:

$ git clone https://github.com/Nipunnyka/tiniShell.git

2. Run:

$ cd tiniShell
$ make tiniShell

or if you need to read inour by fgets() run make tiniShell_r instead.

3. Run ./tiniShell or ./tiniShell_r depending on previous command

Basic Functions and Architecture of tiniShell

Basic framewok of any shell can summarized as (code from Modern Operating Systems) :

#define TRUE 1

while (TRUE) {                   /* repeat forever */ 
  type_prompt();               /* display prompt on the screen */ 
  read_command(command,parameters);     /* read input from terminal */ 
  if (fork()!= 0 ) {                / * the fork Child Process OFF * / 
    / * the Parent code * / 
    waitpid ( - . 1 , & Status, 0 );          / * the wait for Child to Exit * / 
   } the else {
    / * Child code * /
    execve(command,parameters, 0 );    /* execute command */
  }

}

To get the layout that we generally see in CLIs such as:

we have the type_prompt.c which uses commands like getuid() gethostname() and getcwd() to obtain a similar looking layout:

Reading commands

read_command.c reads input and differentiates it into command and parameters. Since I use fgets() backspace is ineffective but this issue will be rectified at a later time. This is where the processing of input strings happens.

UPDATE: using a buffered readLine now without fgets to avoid memory leak, no need to worry for dynamic memory allocation but this functionality requires libreadline5-dev. To facilitate debugging user still has the option to choose what kind of input they require. For fgets() make tiniShell_r should be used.

Built in Commands

Built in Commands are required because commands like cd, pushd, exit, history, export etc cannot exist as executable commands inside a child an need to be built into the shell using system calls (example:chdir() for cd). The analysis and processing of builtin commands should be a function of the interpreter so the main function has to be modified as follows:

if (buildin_command(command,parameters))
     continue ;

The following commands are built into tiniShell with proper error handling: cd, exit,quit, and about. Their implementation can be found in builtin_command.c.

Advanced Functions: Background Execution I/O redirection and piping

I would not go into details about how these function are implemented but would only document their proper usage.

• Background Processing:
  
• I/O Redirection:
  
• Piping: