This is halloShell

blog :- https://my-hallo-project-blogs.hashnode.dev/wonderd-about-a-shell-in-rust

For details about the architecture and design decisions, check out the DESIGN.md.

A minimal shell implemented in Rust.

Right now this minimal shell has:

---

Built-in commands

hallo
cd
echo
pwd
type
complete
jobs
history
declare
exit

Features

Core

• Navigation — cd, pwd
• Quoting / escaping — echo supports single & double quotes and handles backslashes (escape sequences)
• hallo — display a simple banner
• type — check whether a command is built-in
• complete — register or inspect custom completions
• exit — quit the shell
• jobs- helps to see all running and done jobs which are in the background
• history - see all the command you typed till now from the start of the shell
• declare - helps to declare a shell variables

I/O redirection

• > / 1> — stdout (truncate)
• >> / 1>> — stdout (append)
• 2> — stderr (truncate)
• 2>> — stderr (append)

Tip: use > to overwrite, >> to append

Completion

This shell provides flexible completion for commands and filenames, plus a way to register custom completion scripts.

• Command completion

  • Tab — complete the current partial command when a single match exists
  • Tab + Tab — list matching commands for the current partial input
  • Matches include built-in commands and external commands

• Filename completion

  • Tab — complete file or directory names for the current argument
  • Supports nested paths and multiple arguments
  • Tab + Tab — show matching filenames for the current argument
  • A completed directory may receive a trailing / to indicate it's a directory

• Custom completion (the complete built-in)

  • Register: complete -C <script-path> <command> — attach a completion script to <command>
  • Inspect: complete -p <command> — show the registered completion for <command>
  • Unregister: complete -r <command> — remove a registered completion
  • After registration, completions for the command will use the provided script

• Behavior & tips

  • Completion follows the filesystem and command name casing (case-sensitive on case-sensitive systems)
  • Use Tab to save typing and Tab+Tab to explore options
  • if there is common prefix in the command or for file/dirs completeion then the longest common prefix is used

Background Jobs

• if you end a command with & (e.g <command> &) then that is executed in the background it will generate a job number and a pid and we can still use the shell for other commands
• if you want to see all the commands running in the background you can use the built-in command jobs to see
• to check the recent jobs
  • + for the recent command that gone to background
  • - for the second recent command
  • space for rest of the commands
• if it has a Status Running then its still running in Background else then Done means its completed
• if the background job is completed it prints with Done before running another command

Pipelines

• it will help to pass the stdout of one command to the stdin of the another command (e.g <command1> | <command2> command1's stdout will be gone to the stdin for the command2)
• it also support if one of the command is a BUILT_IN command's
• it also support multi command pipelines for external command's

History

• if you want to see all the commands you typed since the start of the shell you use the BUILT-IN command history for viewing
• you can also use flags with a path:
  • -r flag: reads the history from the path provided and add it to the history of the shell
  • -w flag: writes all the history of the shell in to the path script provided
  • -a flag: appends the new history to the path script provided
• there is also support for the arrow key:
  • if pressed <UPARROW> it gives the most recent command typed
  • if pressed <DOWNARROW> it gives the back recent command typed
• also support for env variable HISTFILE if there with the path then it reads the history and add it to the history of the shell on the start
• after hitting exit in the shell the exit is also added to the history of the shell

Parameter Expansion

• you can add your own shell variables with its value with the help of declare BUILT_IN command
• if you want to check if the shell variables exists or not you can do it with the help of -p flag with the shell variable it will print if its there else it well give not present
• it also support expansion so after declaring the variable you can use it other command as $<Variable> if the <Variable> is declared then it will use the value the <Variable> was given
• it also supports expansion as ${<Variable>} for checking for the more appropriate variable declared
• if the ${<Variable>} and the Variable is not declared then it will treat it as empty variable

Note : the shell variable you want to declare must start with a letter or _ and it can contain letters,digits and underscore in the rest of the body

---