/42_minishell

42 project minishell, together with jmuller.

Primary LanguageCMIT LicenseMIT

Minishell (with Bonus)

C

Authors: Martijn Wallage (mwallage), Julian Muller (jmuller)

A project of the 42 Core Curriculum.

About

Minishell is a project in the Core Curriculum of the 42 school. The aim is to recreate part of the Bash shell. The bonus part of the project is to implement the logical operators with parentheses, and wildcards for the current working directory.

Components

Our minishell (called "philoshell", since both authors are philosophers) consists of the following components:

  • READER: takes input from the user, using the readline() function from the gnu readline library. It returns a char *.

  • LEXER: a lexer could be a combination of a TOKENIZER, which splits the input into seperate words or tokens, and a - what shall we call it? - TYPER, which assigns a type to each token. We found, however, that we only really need a TOKENIZER. It returns a char **. If I did this project again, I'd probably use a linked list instead, because it would make insertion and deletion easier.

  • PARSER: takes the char ** that it gets from the TOKENIZER and creates a linked list.

    • Splits the line up into groups that form a simple command, separated by pipes |.
    • handles parentheses as subshells.

  • EXPANDER:

    • Removes redirect information from the command line (this information is by now parsed in our struct).
    • Expands wildcards.
    • Expands variables, after trimming spaces.
    • Removes quotes.

  • EXECUTOR

    • Pipes and forks.
    • Redirects in four ways:
      • < infile: redirect STD_IN to infile.
      • << END: redirect STD_IN to a here_doc which ends with END. If END is without quotation marks, variables inside the heredoc get expanded.
      • > outfile: redirect STD_OUT to outfile, in truncate mode.
      • >> outfile: redirect STD_OUT to outfile, in append mode.
    • Executes each simple command, either as an inbuilt function, a system command (alias) or a path to an executable.
    • On encountering && or ||, checks exitcodes and proceeds accordingly.
      • A && B will run B if and only if A succeeds.
      • A || B will run B if and only if A fails.
    • Runs subshells for pairs of parentheses (). This automatically takes care of priority when parentheses are combined with logical operators.

  • SIGNALS

    • ctrl-c: interrupts child processes and continues to next iteration of while loop.
    • ctrl-d: end-of-file for here-doc and other child processes. If there are no childs, exits shell.
    • ctrl-/: stops child processes, if there are any; otherwise does nothing.