42sh

A shell written in C, the third and final shell project from EPITECH, after minishell1 and minishell2.

• Introduction
• Features

Introduction

The project was done as a group of 5 students:

• Nicolas Polomack (nicolas.polomack@epitech.eu)
• Arthur Knoepflin (arthur.knoepflin@epitech.eu)
• Maxime Jenny (maxime.jenny@epitech.eu)
• Benjamin Solca (benjamin.solca@epitech.eu)
• Ludovic Leuzzi (ludovic.leuzzi@epitech.eu)

The project was to improve upon the minishell2 (who supported at least commands with semi-colons, pipes and redirections) by adding conditionals ('&&' and '||') and the most shell features we can such as aliasing, globbing, history, auto-completion, etc...

This implementation is entirely a continuation of my minishell2 (same original codebase) because it supported a lot of features already with a somewhat maintanable code, so the group was focused on adding features to complete it.

I ensured shell and parser stability, code compatibility and could iterate on feature implementations quicker (since the shell comports code from all the way to my minishell1).

I use the shell everyday as my default shell.
It comports everything I need (except maybe asynchronous job control, sometimes).
So, I am still maintaining it and will probably rewrite it eventually (in Rust, most likely).

Features

The shell launches in interactive mode by default.
It can take a file as an argument and will execute it like a script (therefore supporting being mentioned in shebangs).
It also accepts to evaluate a single line with -c followed by the command.

• Delimiters:
  • Separator (;)
  • Pipes (|)
  • Redirections (<, >, <<, >>)
  • Conditionals (||, &&)
• Redirections:
  • Supports redirecting arbitrary file descriptors (by prepending it, like: ls not-found 2> err)
  • Supports specifying arbitrary file descriptors as redirection targets (like: ls not-found > out 2>&1)
  • Allows combining them with pipes (like: ls * 2>&1 | hexdump -C allows hexdump to work on both the stdout and stderr of ls)
• Quote types:
  • Double quotes: Expands variables like $PATH and ${PATH}, disables file globbing such as * and ?
  • Single quotes: Disables everything, even backslashes
  • Magic quotes (aka. backticks, aka. backquotes): Triggers Command substitution
• Line Editing:
  • Auto-completion for commands and filenames
  • Advanced line edition with cursor, arrow-keys if terminal supported, will fallback to standard stdin read otherwise
  • Variable expansions, from environment, positional arguments and built-in variables (from the set command)
  • Last exit code ($?)
  • Shell PID ($$)
  • Last argument from last command ($!)
  • Count of current positional arguments ($#)
  • Whole positional argument list, except the first one which is the script's name ($@)
  • Last argument from last command ($!)
  • Whole last command (!!)
  • N-th argument from last command (!:n)
  • File globbing with *, ?, [a-z] and {foo,bar}
  • Command substitution with `...` and $(...)
• Aliases:
  • alias and unalias built-in commands
  • Aliases all the commands in the evaluated line
  • Self-aliasing supported
  • Alias loops are detected and prevented early
  • Aliases are saved upon exit and loaded on launch
  • Special aliases:
    • precmd: before typing a command
    • postcmd: after typing a command
    • cwdcmd: after changing directory
  • Stored in ~/.42sh_alias
• History:
  • history built-in command
  • Saved in ~/.42sh_history
• Environement:
  • env, setenv and unsetenv built-in commands
  • env -i supported Temporarily removed
  • Environment variables can be saved by writing them in ~/.42shrc
• Variables:
  • set and unset built-in commands
  • Can be used for expansions
  • ${pid}, ${ppid}, ${uid}, ${euid}, ${gid}, ${pgid} and ${sid} are set by default on launch
  • Last command's execution time in seconds (with ${exec_duration})
  • Last command's execution time human-formatted in sensible units (with ${exec_duration_fmt})
• Prompts:
  • prompt built-in command
  • 11 prompts to choose from
  • Prompt customization through the PS1 environment variable
  • Command substitution in prompts with \(...) syntax in the PS1 environment variable
  • Can be saved by setting the PROMPT environment variable with the prompt ID number
• Other built-in commands:
  • where and which
  • cd: To change directory (supports - to go back to previous directory)
  • exit: To exit the shell (supports an exit code as argument)
  • exec: Executes a command, in place of the current shell
  • echo: To print stuff (supports -n)
  • builtins: To list the available builtins