readline_callback_handler_install() installs an asynchronous readline line-input callback. This guide explains the function with focused examples and the decisions that matter in real applications.
What Is readline_callback_handler_install() in PHP?
Installs an asynchronous readline line-input callback.
A typical call looks like this:
<?php
readline_callback_handler_install($prompt, $callback);
The input arguments shown in the call identify the relevant connection, resource, value, path or configuration for the operation. Pay attention to argument order and to the return value demonstrated below.
Example 1: Basic Usage
This first example uses readline_callback_handler_install() directly to demonstrate its basic purpose.
<?php
readline_callback_handler_install("Command: ", function (string $line): void { echo $line; });
The returned value illustrates installs an asynchronous readline line-input callback. The callback runs only when input is serviced; this is for CLI event loops.
Example 2: A Different Input or Option
The next example changes the input or option, showing another supported use of readline_callback_handler_install().
<?php
readline_callback_handler_install("Name: ", function (string $line): void { echo trim($line); });
The returned value illustrates installs an asynchronous readline line-input callback. The callback runs only when input is serviced; this is for CLI event loops.
Practical Example: Applying the Function
In application code, readline_callback_handler_install() belongs in a controlled workflow with input validation, a checked result and cleanup where needed.
<?php
readline_callback_handler_install("Input: ", function (string $line): void { echo strtoupper($line); }); // In a CLI event loop, call readline_callback_read_char() when input is ready.
The returned value illustrates installs an asynchronous readline line-input callback. The callback runs only when input is serviced; this is for CLI event loops.
Important Behavior and Edge Cases
- Main behavior: Installs an asynchronous readline line-input callback.
- Important limitation: The callback runs only when input is serviced; this is for CLI event loops.
- Requirements: This function uses the CLI readline extension; it is not designed for an ordinary web request.
Comparison With Related Functions
| Function or Approach | When to Use It |
|---|---|
readline_callback_handler_install() | Installs an asynchronous readline line-input callback. |
readline_callback_read_char | Consumes one available input character for readline callback handling. |
Common Beginner Mistakes
| Mistake | Correct Approach |
|---|---|
Ignoring the specific limits or preconditions of readline_callback_handler_install(). | The callback runs only when input is serviced; this is for CLI event loops. |
| Assuming every environment produces the same result. | This function uses the CLI readline extension; it is not designed for an ordinary web request. |
Key Takeaways
- Installs an asynchronous readline line-input callback.
- The callback runs only when input is serviced; this is for CLI event loops.
- This function uses the CLI readline extension; it is not designed for an ordinary web request.
Use readline_callback_handler_install() when its behavior matches your task, and verify the relevant return value before taking further action. The output depends on the local configuration when it uses resources, files or an interactive terminal.