PHP Regex get command from a chat - php

Question

Im currently developing a AJAX based chat, and i'm trying to get to the part where i can input commands in the chat as in this example:
"/roll 20" will give a random number between 1 and 20.
And i thought it would be best to fetch commands with regex, but i cant get the values from the string and this is what i've tried.
$message = "/roll 20";
preg_match("/roll \d+", $message, $matches);
print_r($matches);
I would like to get "/roll 20" from the message but it wont print any matches. So is it that my regex is wrong or am i handling the preg_match wrong?
ps. If you have another PHP based style to fetch commands with, i'l gladly take a look.

Answer 1

You'd need to use delimiters around the regex and also add regex to catch the beginning and end of a string. I've also wrapped the roll amount in parameters so you get a variable for the roll amount. So a phrase with the /roll command in the middle of the input wouldn't be caught.
$message = "/roll 20";
preg_match("#^/roll (\d+)$#", $message, $matches);
print_r($matches);

Answer 2

I honestly don't see why you would use regex for this. I assume you only have a fixed set of commands against which you might be matching, and that you would only issue such commands when the input starts with /. And that the command would need to come as first item in line and have parameters to the command separated by spaces.
So, using preg_match() you would need to have a series of patterns that you loop through to compare the line. This could become bulky to maintain.
I would propose a different parser-like approach, using explode to break apart the input line, inspecting the first element to see if it is a command. If so, you collect the parameters and call a function to do what you want to do.
$input = '/roll 20';
$commands = array(
'roll' => array('range'), // single parameter
'foo' => array('param1', 'param2'), // multiple parameters
'bar' => array() // no parameters
);
$input_array = explode(' ', $input);
$command = ltrim($input_array[0], '/');
if (strpos($input_array[0], '/') === 0 && array_key_exists($command, $commands)) {
$parameters = array();
$i = 1;
foreach($commands[$command] as $param_key) {
if(empty($input_array[$i])) {
// error we did not get expected number of parameters
// handle this error somehow
die('Not enough parameters passed for command');
} else {
$parameters[$param_key] = $input_array[$i];
$i++;
}
}
// perhaps have a function defined for each command that you can call
// while passing in the parameter array
call_user_func($command, $parameters);
} else {
// this is just text content
// do whatever
}
No need for the relatively slow regex functionality.

Answer 3

Use delimiter for your regex:
preg_match("~/roll \d+~", $message, $matches);
^ ^

Answer 4

Use Delimiter
preg_match("#/roll \d+#", $message, $matches);