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42sh

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

Introduction

The project was done as a group of 5 students:

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