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clue/reactphp-stdio

Async, event-driven and UTF-8 aware console input & output (STDIN, STDOUT) for truly interactive CLI applications, built on top of ReactPHP.

You can use this library to build truly interactive and responsive command line (CLI) applications, that immediately react when the user types in a line or hits a certain key. Inspired by ext-readline, but supports UTF-8 and interleaved I/O (typing while output is being printed), history and autocomplete support and takes care of proper TTY settings under the hood without requiring any extensions or special installation.

Table of contents

• Support us
• Quickstart example
• Usage
  • Stdio
    • Output
    • Input
    • Prompt
    • Echo
    • Input buffer
    • Cursor
    • History
    • Autocomplete
    • Keys
    • Bell
  • Readline
• Pitfalls
• Install
• Tests
• License
• More

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Quickstart example

Once installed, you can use the following code to present a prompt in a CLI program:

See also the examples.

Usage

Stdio

The Stdio is the main interface to this library. It is responsible for orchestrating the input and output streams by registering and forwarding the corresponding events.

This class takes an optional LoopInterface|null $loop parameter that can be used to pass the event loop instance to use for this object. You can use a null value here in order to use the default loop. This value SHOULD NOT be given unless you're sure you want to explicitly use a given event loop instance.

See below for waiting for user input and writing output. The Stdio class is a well-behaving duplex stream (implementing ReactPHP's DuplexStreamInterface) that emits each complete line as a data event, including the trailing newline.

Output

The Stdio is a well-behaving writable stream implementing ReactPHP's WritableStreamInterface.

The write($text) method can be used to print the given text characters to console output. This is useful if you need more control or want to output individual bytes or binary output:

Because the Stdio is a well-behaving writable stream, you can also pipe() any readable stream into this stream.

Input

The Stdio is a well-behaving readable stream implementing ReactPHP's ReadableStreamInterface.

It will emit a data event for every line read from console input. The event will contain the input buffer as-is, including the trailing newline. You can register any number of event handlers like this:

Note that this class takes care of buffering incomplete lines and will only emit complete lines. This means that the line will usually end with the trailing newline character. If the stream ends without a trailing newline character, it will not be present in the data event. As such, it's usually recommended to remove the trailing newline character before processing command line input like this:

Similarly, if you copy and paste a larger chunk of text, it will properly emit multiple complete lines with a separate data event for each line.

Because the Stdio is a well-behaving readable stream that will emit incoming data as-is, you can also use this to pipe() this stream into other writable streams.

You can control various aspects of the console input through this interface, so read on..

Prompt

The prompt will be written at the beginning of the user input line, right before the user input buffer.

The setPrompt($prompt) method can be used to change the input prompt. The prompt will be printed to the user input line as-is, so you will likely want to end this with a space:

The default input prompt is empty, i.e. the user input line contains only the actual user input buffer. You can restore this behavior by passing an empty prompt:

The getPrompt() method can be used to get the current input prompt. It will return an empty string unless you've set anything else:

Echo

The echo mode controls how the actual user input buffer will be presented in the user input line.

The setEcho($echo) method can be used to control the echo mode. The default is to print the user input buffer as-is.

You can disable printing the user input buffer, e.g. for password prompts. The user will still be able to type, but will not receive any indication of the current user input buffer. Please note that this often leads to a bad user experience as users will not even see their cursor position. Simply pass a boolean false like this:

Alternatively, you can also hide the user input buffer by using a replacement character. One replacement character will be printed for each character in the user input buffer. This is useful for password prompts to give users an indicatation that their key presses are registered. This often provides a better user experience and allows users to still control their cursor position. Simply pass a string replacement character likes this:

To restore the original behavior where every character appears as-is, simply pass a boolean true:

Input buffer

Everything the user types will be buffered in the current user input buffer. Once the user hits enter, the user input buffer will be processed and cleared.

The addInput($input) method can be used to add text to the user input buffer at the current cursor position. The given text will be inserted just like the user would type in a text and as such adjusts the current cursor position accordingly. The user will be able to delete and/or rewrite the buffer at any time. Changing the user input buffer can be useful for presenting a preset input to the user (like the last password attempt). Simply pass an input string like this:

The setInput($buffer) method can be used to control the user input buffer. The given text will be used to replace the entire current user input buffer and as such adjusts the current cursor position to the end of the new buffer. The user will be able to delete and/or rewrite the buffer at any time. Changing the user input buffer can be useful for presenting a preset input to the user (like the last password attempt). Simply pass an input string like this:

The getInput() method can be used to access the current user input buffer. This can be useful if you want to append some input behind the current user input buffer. You can simply access the buffer like this:

Cursor

By default, users can control their (horizontal) cursor position by using their arrow keys on the keyboard. Also, every character pressed on the keyboard advances the cursor position.

The setMove($toggle) method can be used to control whether users are allowed to use their arrow keys. To disable the left and right arrow keys, simply pass a boolean false like this:

To restore the default behavior where the user can use the left and right arrow keys, simply pass a boolean true like this:

The getCursorPosition() method can be used to access the current cursor position, measured in number of characters. This can be useful if you want to get a substring of the current user input buffer. Simply invoke it like this:

The getCursorCell() method can be used to get the current cursor position, measured in number of monospace cells. Most normal characters (plain ASCII and most multi-byte UTF-8 sequences) take a single monospace cell. However, there are a number of characters that have no visual representation (and do not take a cell at all) or characters that do not fit within a single cell (like some Asian glyphs). This method is mostly useful for calculating the visual cursor position on screen, but you may also invoke it like this:

The moveCursorTo($position) method can be used to set the current cursor position to the given absolute character position. For example, to move the cursor to the beginning of the user input buffer, simply call:

The moveCursorBy($offset) method can be used to change the cursor position by the given number of characters relative to the current position. A positive number will move the cursor to the right - a negative number will move the cursor to the left. For example, to move the cursor one character to the left, simply call:

History

By default, users can access the history of previous commands by using their UP and DOWN cursor keys on the keyboard. The history will start with an empty state, thus this feature is effectively disabled, as the UP and DOWN cursor keys have no function then.

Note that the history is not maintained automatically. Any input the user submits by hitting enter will not be added to the history automatically. This may seem inconvenient at first, but it actually gives you more control over what (and when) lines should be added to the history. If you want to automatically add everything from the user input to the history, you may want to use something like this:

The listHistory(): string[] method can be used to return an array with all lines in the history. This will be an empty array until you add new entries via addHistory().

The addHistory(string $line): void method can be used to add a new line to the (bottom position of the) history list. A following listHistory() call will return this line as the last element.

The clearHistory(): void method can be used to clear the complete history list. A following listHistory() call will return an empty array until you add new entries via addHistory() again. Note that the history feature will effectively be disabled if the history is empty, as the UP and DOWN cursor keys have no function then.

The limitHistory(?int $limit): void method can be used to set a limit of history lines to keep in memory. By default, only the last 500 lines will be kept in memory and everything else will be discarded. You can use an integer value to limit this to the given number of entries or use null for an unlimited number (not recommended, because everything is kept in RAM). If you set the limit to 0 (int zero), the history will effectively be disabled, as no lines can be added to or returned from the history list. If you're building a CLI application, you may also want to use something like this to obey the HISTSIZE environment variable:

There is no such thing as a readHistory() or writeHistory() method because filesystem operations are inherently blocking and thus beyond the scope of this library. Using your favorite filesystem API and an appropriate number of addHistory() or a single listHistory() call respectively should be fairly straight forward and is left up as an exercise for the reader of this documentation (i.e. you).

Autocomplete

By default, users can use autocompletion by using their TAB keys on the keyboard. The autocomplete function is not registered by default, thus this feature is effectively disabled, as the TAB key has no function then.

The setAutocomplete(?callable $autocomplete): void method can be used to register a new autocomplete handler. In its most simple form, you won't need to assign any arguments and can simply return an array of possible word matches from a callable like this:

If the user types he [TAB], the first two matches will be skipped as they do not match the current word prefix and the last one will be picked automatically, so that the resulting input buffer is hello.

If the user types e [TAB], then this will match multiple entries and the user will be presented with a list of up to 8 available word completions to choose from like this:

Unless otherwise specified, the matches will be performed against the current word boundaries in the input buffer. This means that if the user types hello [SPACE] ex [TAB], then the resulting input buffer is hello exit, which may or may not be what you need depending on your particular use case.

In order to give you more control over this behavior, the autocomplete function actually receives three arguments (similar to ext-readline's readline_completion_function()): The first argument will be the current incomplete word according to current cursor position and word boundaries, while the second and third argument will be the start and end offset of this word within the complete input buffer measured in (Unicode) characters. The above examples will be invoked as $fn('he', 0, 2), $fn('e', 0, 1) and $fn('ex', 6, 8) respectively. You may want to use this as an $offset argument to check if the current word is an argument or a root command and the $word argument to autocomplete partial filename matches like this:

Note that the user may also use quotes and/or leading whitespace around the root command, for example "hell [TAB], in which case the offset will be advanced such as this will be invoked as $fn('hell', 1, 4). Unless you use a more sophisticated argument parser, a decent approximation may be using $offset <= 1 to check this is a root command.

If you need even more control over autocompletion, you may also want to access and/or manipulate the cursor directly like this:

You can use a null value to remove the autocomplete function again and thus disable the autocomplete function:

Keys

The Readline class is responsible for reading user input from STDIN and registering appropriate key events. By default, Readline uses a hard-coded key mapping that resembles the one usually found in common terminals. This means that normal Unicode character keys ("a" and "b", but also "?", "ä", "µ" etc.) will be processed as user input, while special control keys can be used for history and autocomplete functions. Unknown special keys will be ignored and will not processed as part of the user input by default.

Additionally, you can bind custom functions to any key code you want. If a custom function is bound to a certain key code, the default behavior will no longer trigger. This allows you to register entirely new functions to keys or to overwrite any of the existing behavior.

For example, you can use the following code to print some help text when the user hits a certain key:

Similarly, this can be used to manipulate the user input and replace some of the input when the user hits a certain key:

The Readline uses raw binary key codes as emitted by the terminal. This means that you can use the normal UTF-8 character representation for normal Unicode characters. Special keys use binary control code sequences (refer to ANSI / VT100 control codes for more details). For example, the following code can be used to register a custom function to the UP arrow cursor key:

Bell

By default, this project will emit an audible/visible BELL signal when the user tries to execute an otherwise disabled function, such as using the left or backspace keys when already at the beginning of the line.

Whether or not the BELL is audible/visible depends on the termin and its settings, i.e. some terminals may "beep" or flash the screen or emit a short vibration.

The setBell(bool $bell): void method can be used to enable or disable emitting the BELL signal when using a disabled function:

Readline

Deprecated since v2.3.0, see Stdio instead.

The deprecated Readline class is responsible for reacting to user input and presenting a prompt to the user. It does so by reading individual bytes from the input stream and writing the current user input line to the output stream.

The deprecated Readline class is only used internally and should no longer be referenced from consuming projects.

You can access the current instance through the Stdio:

All methods that are available on the Readline instance are now available on the Stdio class. For BC reasons, they remain available on the Readline class until the next major release, see also above for more details.

Internally, the Readline is also a well-behaving readable stream (implementing ReactPHP's ReadableStreamInterface) that emits each complete line as a data event, including the trailing newline. This is considered advanced usage.

Pitfalls

The Stdio has to redraw the current user input line whenever output is written to the STDOUT. Because of this, it is important to make sure any output is always written like this instead of using echo statements:

Depending on your program, it may or may not be reasonable to replace all such occurrences. As an alternative, you may utilize output buffering that will automatically forward all write events to the Stdio instance like this:

Install

The recommended way to install this library is through Composer. New to Composer?

This project follows SemVer. This will install the latest supported version:

See also the CHANGELOG for details about version upgrades.

This project aims to run on any platform and thus does not require any PHP extensions and supports running on legacy PHP 5.3 through current PHP 8+ and HHVM. It's highly recommended to use the latest supported PHP version for this project.

Internally, it will use the ext-mbstring to count and measure string sizes. If this extension is missing, then this library will use a slightly slower Regex work-around that should otherwise work equally well. Installing ext-mbstring is highly recommended.

Internally, it will use the ext-readline to enable raw terminal input mode. If this extension is missing, then this library will manually set the required TTY settings on start and will try to restore previous settings on exit. Input line editing is handled entirely within this library and does not rely on ext-readline. Installing ext-readline is entirely optional.

Note that Microsoft Windows is not supported. Due to platform constraints, PHP does not provide support for reading from standard console input without blocking on Windows. Unfortunately, until the underlying PHP feature request is implemented (which is unlikely to happen any time soon), there's little we can do in this library. However, this package does work on Windows Subsystem for Linux (or WSL) without issues. We suggest installing WSL when you want to run this package on Windows. See also #18 for more details.

Tests

To run the test suite, you first need to clone this repo and then install all dependencies through Composer:

To run the test suite, go to the project root and run:

License

This project is released under the permissive MIT license.

Did you know that I offer custom development services and issuing invoices for sponsorships of releases and for contributions? Contact me (@clue) for details.

More

• If you want to learn more about processing streams of data, refer to the documentation of the underlying react/stream component.

• If you build an interactive CLI tool that reads a command line from STDIN, you may want to use clue/arguments in order to split this string up into its individual arguments and then use clue/commander to route to registered commands and their required arguments.