minishell

A project where we have to make our own shell!

Index:

• Example-yo

What is a shell?

Diving tasks, execution and parsing

Environment variables

They are variables that exist in the environment of a process. Any following child processes will inherit the environment variables from the parent, but any changes made in a child won't affect the environment of the parent. Environment variables can be initialized in different scopes, like globally across your entire system or on the user-level. In Linux global variables can be found in etc/environment and user-specific ones in ~.profile

Why built-ins?

There are two types of commands, external programs and built-in functions executed from within the shell. A regular command is a program that can be found in one of the folders specified in the environment variable: Path and will be excecuted with execv, which has to be done in a child process, as the program executed from execv will take over the process and you wouldn't be able to control it in any way afterwards.

A builtin would simply look like a function executed inside your program. There are several reasons why it may be used:

• It's much faster to execute and less resource intensive, which is why it's more efficient for commonly used commands to be built in the shell, like echo and cd.
• Commands that need to be able to change the environment of the shell, can't be executed externally:
  • cd and pwd need to be able to work from the current working directory, which is specific to a process.
  • export, unset and env change the environment variables. In a child process, any changes to these would only persist for the lifetime of the child.
  • exit because it can only exit the current process.

Executing in child vs parent

Redirection and pipe/command groups

Conquerent vs sequential execution

Signals

Exit status