# readline_callback_handler_install

(PHP 5 >= 5.1.0)

readline_callback_handler_install — Initializes the readline callback interface and terminal, prints the prompt and returns immediately

### Description

bool readline_callback_handler_install ( string `$prompt` , callback `$callback` )

Sets up a readline callback interface then prints `prompt` and immediately returns. Calling this function twice without removing the previous callback interface will automatically and conveniently overwrite the old interface.

The callback feature is useful when combined with stream_select() as it allows interleaving of IO and user input, unlike readline().

### Parameters

`prompt`

  The prompt message.

`callback`

  The `callback` function takes one parameter; the user input returned.

### Return Values

Returns `TRUE` on success or `FALSE` on failure.

### Examples

Example#1 Readline Callback Interface Example

`<?php
function rl_callback($ret)
{
global $c, $prompting;
echo "You entered: $ret\n";
$c++;
if ($c > 10) {
$prompting = false;
readline_callback_handler_remove();
} else {
readline_callback_handler_install("[$c] Enter something: ", 'rl_callback');
}
}
$c = 1;
$prompting = true;
readline_callback_handler_install("[$c] Enter something: ", 'rl_callback');
while ($prompting) {
$w = NULL;
$e = NULL;
$n = stream_select($r = array(STDIN), $w, $e, null);
if ($n && in_array(STDIN, $r)) {
// read a character, will call the callback when a newline is entered
readline_callback_read_char();
}
}
echo "Prompting disabled. All done.\n";
?>`

### See Also

- readline_callback_handler_remove()
- readline_callback_read_char()
- stream_select()