A readline replacement written in Rust

Introduction

Reedline is a project to create a line editor (like bash's readline or zsh's zle) that supports many of the modern conveniences of CLIs, including syntax highlighting, completions, multiline support, Unicode support, and more. It is currently primarily developed as the interactive editor for nushell (starting with v0.60) striving to provide a pleasant interactive experience.

Outline

• Examples
  • Quickstart example
  • Keybinding configuration example
  • History example
  • Syntax highlighting example
  • Interactive tab-completion example
  • Fish-style history autosuggestions
  • Line validation example
  • Vi-style edit mode example
• Development status
• Contributing
• Alternatives

Examples

For the full documentation visit https://docs.rs/reedline. The examples should highlight how you enable the most important features or which traits can be implemented for language-specific behavior.

Basic example

// Create a default reedline object to handle user input

use reedline::{DefaultPrompt, Reedline, Signal};
use std::io;

fn main() -> io::Result<()> {
    let mut line_editor = Reedline::create()?;
    let prompt = DefaultPrompt::default();

    loop {
        let sig = line_editor.read_line(&prompt)?;
        match sig {
            Signal::Success(buffer) => {
                println!("We processed: {}", buffer);
            }
            Signal::CtrlD | Signal::CtrlC => {
                println!("\nAborted!");
                break Ok(());
            }
        }
    }
}

Integrate with custom keybindings

// Configure reedline with custom keybindings

//Cargo.toml
//  [dependencies]
//  crossterm = "*"

use {
  crossterm::event::{KeyCode, KeyModifiers},
  reedline::{default_emacs_keybindings, EditCommand, Reedline},
};

let mut keybindings = default_emacs_keybindings();
keybindings.add_binding(
  KeyModifiers::ALT,
  KeyCode::Char('m'),
  vec![EditCommand::BackspaceWord],
);

let mut line_editor = Reedline::create().with_keybindings(keybindings);

Integrate with History

// Create a reedline object with history support, including history size limits

use reedline::{FileBackedHistory, Reedline};

let history = Box::new(
  FileBackedHistory::with_file(5, "history.txt".into())
    .expect("Error configuring history with file"),
);
let mut line_editor = Reedline::create()
  .with_history(history);

Integrate with custom syntax Highlighter

// Create a reedline object with highlighter support

use reedline::{ExampleHighlighter, Reedline};

let commands = vec![
  "test".into(),
  "hello world".into(),
  "hello world reedline".into(),
  "this is the reedline crate".into(),
];
let mut line_editor =
Reedline::create().with_highlighter(Box::new(ExampleHighlighter::new(commands)));

Integrate with custom tab completion

// Create a reedline object with tab completions support

use reedline::{ColumnarMenu, DefaultCompleter, Reedline, ReedlineMenu};

let commands = vec![
  "test".into(),
  "hello world".into(),
  "hello world reedline".into(),
  "this is the reedline crate".into(),
];
let completer = Box::new(DefaultCompleter::new_with_wordlen(commands.clone(), 2));
// Use the interactive menu to select options from the completer
let completion_menu = Box::new(ColumnarMenu::default().with_name("completion_menu"));

let mut line_editor =
Reedline::create().with_completer(completer).with_menu(ReedlineMenu::EngineCompleter(completion_menu));

Integrate with Hinter for fish-style history autosuggestions

// Create a reedline object with in-line hint support

//Cargo.toml
//  [dependencies]
//  nu-ansi-term = "*"

use {
  nu_ansi_term::{Color, Style},
  reedline::{DefaultHinter, Reedline},
};

let mut line_editor = Reedline::create().with_hinter(Box::new(
  DefaultHinter::default()
  .with_style(Style::new().italic().fg(Color::LightGray)),
));

Integrate with custom line completion Validator

// Create a reedline object with line completion validation support

use reedline::{DefaultValidator, Reedline};

let validator = Box::new(DefaultValidator);

let mut line_editor = Reedline::create().with_validator(validator);

Use custom EditMode

// Create a reedline object with custom edit mode
// This can define a keybinding setting or enable vi-emulation

use reedline::{
    default_vi_insert_keybindings, default_vi_normal_keybindings, EditMode, Reedline, Vi,
};

let mut line_editor = Reedline::create().with_edit_mode(Box::new(Vi::new(
    default_vi_insert_keybindings(),
    default_vi_normal_keybindings(),
)));

Are we prompt yet? (Development status)

Reedline has now all the basic features to become the primary line editor for nushell

• General editing functionality, that should feel familiar coming from other shells (e.g. bash, fish, zsh).
• Configurable keybindings (emacs-style bindings and basic vi-style).
• Configurable prompt
• Content-aware syntax highlighting.
• Autocompletion (With graphical selection menu or simple cycling inline).
• History with interactive search options (optionally persists to file, can support multiple sessions accessing the same file)
• Fish-style history autosuggestion hints
• Undo support.
• Clipboard integration
• Line completeness validation for seamless entry of multiline command sequences.

Areas for future improvements

• Support for Unicode beyond simple left-to-right scripts
• Easier keybinding configuration
• Support for more advanced vi commands
• Visual selection
• Smooth experience if completion or prompt content takes long to compute
• Support for a concurrent output stream from background tasks to be displayed, while the input prompt is active. ("Full duplex" mode)

For more ideas check out the feature discussion or hop on the #reedline channel of the nushell discord.

Development history

If you want to follow along with the history of how reedline got started, you can watch the recordings of JT's live-coding streams.

Playlist: Creating a line editor in Rust

Alternatives

For currently more mature Rust line editing check out:

• rustyline