NAME

Terminal::LineEditor - Generalized terminal line editing

SYNOPSIS

### PREP

use Terminal::LineEditor;
use Terminal::LineEditor::RawTerminalInput;

# Create a basic CLI text input object
my $cli = Terminal::LineEditor::CLIInput.new;


### BASICS

# Preload some input history
$cli.load-history($history-file);
$cli.add-history('synthetic input', 'more synthetic input');

# Prompt for input, supporting common edit commands,
# scrolling the field to stay on one line
my $input = $cli.prompt('Please enter your thoughts: ');

# Prompt for a password, masking with asterisks (suppresses history)
my $pass  = $cli.prompt('Password: ', mask => '*');

# Prompt defaults to empty
my $stuff = $cli.prompt;

# Review and save history
.say for $cli.history;
$cli.save-history($history-file);


### TYPICAL USE

loop {
    # Get user's input
    my $in = $cli.prompt("My prompt >");

    # Exit loop if user indicated finished
    last without $in;

    # Add line to history if it is non-empty
    $cli.add-history($in) if $in.trim;

    # Do something with the input line; here we just echo it
    say $in;
}

DESCRIPTION

Terminal::LineEditor is a terminal line editing package similar to Linenoise or Readline, but not a drop-in replacement for either of them. Terminal::LineEditor has a few key design differences:

• Implemented in pure Raku; Linenoise and Readline are NativeCall wrappers.

• Features strong separation of concerns; all components are exposed and replaceable.

• Useable both directly for simple CLI apps and embedded in TUI interfaces.

Use with Rakudo REPL

A PR for Rakudo has been created to allow Terminal::LineEditor to be used as the REPL line editor when Rakudo is used in interactive mode. If your Rakudo build includes this PR, you can set the following in your environment to use Terminal::LineEditor by default:

export RAKUDO_LINE_EDITOR=LineEditor

If the environment variable is not specified, but Terminal::LineEditor is the only line editing module installed, Rakudo will auto-detect and enable it.

Default Keymap

The latest version of the default keymap is specified in Terminal::LineEditor::KeyMappable.default-keymap(), but the below represents the currently implemented, commonly used keys:

Commonly Used Keys

KEY	FUNCTION	NOTES
Ctrl-A	move-to-start
Ctrl-B	move-char-back
Ctrl-C	abort-input
Ctrl-D	abort-or-delete	Abort if empty, or delete-char-forward
Ctrl-E	move-to-end
Ctrl-F	move-char-forward
Ctrl-H	delete-char-back
Ctrl-J	finish	LF (Line Feed)
Ctrl-K	delete-to-end
Ctrl-L	refresh-all
Ctrl-M	finish	CR (Carriage Return)
Ctrl-N	history-next
Ctrl-P	history-prev
Ctrl-T	swap-chars
Ctrl-U	delete-to-start
Ctrl-V	literal-next
Ctrl-W	delete-word-back
Ctrl-Y	yank
Ctrl-Z	suspend
Ctrl-_	undo	Ctrl-Shift-<hyphen> on some keyboards
Backspace	delete-char-back
CursorLeft	move-char-back
CursorRight	move-char-forward
CursorHome	move-to-start
CursorEnd	move-to-end
CursorUp	history-prev
CursorDown	history-next
Alt-b	move-word-back
Alt-c	tclc-word	Readline treats this as Capitalize
Alt-d	delete-word-forward
Alt-f	move-word-forward
Alt-l	lowercase-word
Alt-t	swap-words
Alt-u	uppercase-word
Alt-<	history-start	Alt-Shift-<comma> on some keyboards
Alt->	history-end	Alt-Shift-<period> on some keyboards

All bindable edit functions are defined in the Terminal::LineEditor::SingleLineTextInput role (in each corresponding method beginning with edit-) or is one of the following special actions:

Special Actions

ACTION	MEANING
abort-input	Throw away input so far and return an undefined Str
abort-or-delete	abort-input if empty, otherwise delete-char-forward
finish	Accept and return current input line
literal-next	Insert a literal control character into the buffer
suspend	Suspend the program with SIGTSTP, wait for SIGCONT
history-start	Switch input to first line in history
history-prev	Switch input to previous line in history
history-next	Switch input to next line in history
history-end	Switch input to last line in history (the partial input)

Architecture

Terminal::LineEditor is built up in layers, starting from the most abstract:

• EditableBuffer -- Basic interface role for editable buffers of all sorts

• SingleLineTextBuffer -- An EditableBuffer that knows how to apply simple insert/delete/replace operations at arbitrary positions/ranges, tracks a yank item (the most recently deleted text), and creates and manages undo/redo information to allow infinite undo

• SingleLineTextBuffer::Cursor -- A cursor class that knows how to move around within a SingleLineTextBuffer without moving outside the content area, and knows whether edit operations should automatically adjust its position

• SingleLineTextBuffer::WithCursors -- A wrapper of SingleLineTextBuffer that supports multiple simultaneous cursors, and handles automatically updating them appropriately whenever applying a basic edit operation

• SingleLineTextInput -- An input field role that tracks its own insert position as an auto-updating cursor, and provides a range of edit methods that operate relative to the current insert position

• ScrollingSingleLineInput -- A SingleLineTextInput that knows how to scroll within a limited horizontal display width to ensure that the insert position is always visible, no longer how long the input

• ScrollingSingleLineInput::ANSI -- A further extension of ScrollingSingleLineInput that is aware of cursor position and movement using ANSI/VT escape codes

• CLIInput -- A driver for ScrollingSingleLineInput::ANSI that deals with raw terminal I/O, detects terminal size and cursor position, supports a control key map for common edit operations, and handles suspend/resume without corrupting terminal state

Edge Cases

There are a few edge cases for which Terminal::LineEditor chose one of several possible behaviors. Here's the reasoning for each of these otherwise arbitrary decisions:

• Attempting to apply an edit operation or create a new cursor outside the buffer contents throws an exception, because these indicate a logic error elsewhere.

• Attempting to move a previously correct cursor outside the buffer contents silently clips the new cursor position to the buffer endpoints, because users frequently hold down cursor movement keys (and thus repeatedly try to move past an endpoint).

• Undo'ing a delete operation, where one or more cursors were within the deleted region, results in all such cursors moving to the end of the undo; this is consistent with the behavior of an insert operation at the same position as the delete undo.

• For the same reason as for delete operations, replace operations that overlap cursor locations will move them to the end of the replaced text.

Unmapped Functionality

Some of the functionality supported by lower layers of Terminal::LineEditor is not exposed in the default keymap of Terminal::LineEditor::KeyMappable. This is generally because no commonly-agreed shell keys map to this functionality.

For example, Terminal::LineEditor::SingleLineTextBuffer can treat replace as an atomic operation, but basic POSIX shells generally don't; they instead expect the user to delete and insert as separate operations.

That said, if I've missed a commonly-supported key sequence for any of the unmapped functionality, please open an issue for this repository with a link to the relevant docs so I can expand the default keymap.

AUTHOR

Geoffrey Broadwell [email protected]

COPYRIGHT AND LICENSE

Copyright 2021-2024 Geoffrey Broadwell

This library is free software; you can redistribute it and/or modify it under the Artistic License 2.0.