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Minishell

Minishell Project

→ As beautiful as a shell

Minishell is a 42-school project that aims to introduce us to the world of shells by recoding our mini-bash, a program that can parse, execute, and launch executables along with some built-in commands.

→ Used functions :

readline, rl_clear_history, rl_on_new_line, rl_replace_line, rl_redisplay, add_history, printf, malloc, free, write, access, open, read, close, fork, waitpid, signal, kill, exit, getcwd, chdir, execve, dup2, pipe, perror.

This is an overview of the project :

→ Lexer :

• input: Readline output

• output: tokenized linked list

• the objective of this step is to split the readline output using tokens (defined macros)

• used tokens: WORD, REDIRECTION, PIPE, AND, SEMI, PARENTHESIS

→ Syntax analyzer:

• input: tokenized linked list

• output:

  • in case of no syntax error: same tokenized linked list.

  • in case of a syntax error: printed error type.

• the objective of this step is to check all possible command syntax errors (if you have a doubt about an error take bash as a reference).

→ Parser :

• input: tokenized linked list

• output: commands linked list

• we can split this step into 2 sub-steps

  • handling redirections (input, output, append, heredoc).

  • add command to the linked list with their file descriptors (in and out).

→ Execution :

• input: commands linked list

• if everything went okay in the past steps we have 2 different cases to communicate between the commands (processes):

  • if there are $`N`$ commands we initialize $`N-1`$ pipes to communicate between the processes we create.

  • In another case, if there’s some kind of redirection, it takes the priority

• the only step left is to verify if the command is available or not there are two ways to handle it depending on the command itself

  • relative path

  • absolute path

• in this part, the commands are ready to be executed

What is Env or Environment?

• shell maintains an environment that includes a set of variables defined by a name, a user initialization, and system initialization.

  • sources that can help you like us:

    • what is env?

What is Lexer or Tokenization?

• Tokenization is a way of separating a sentence into smaller units called tokens,

  • Sources that can help you like us:

    • what is a lexer?

    • what is a lexer and how does it work?

    • What is Tokenization?

What is Syntax Analysis:

• It analyses the syntactical structure and checks if the given input is in the correct syntax of the programming language or not.