preg_replace : how get what is replaced - php

Question

I want to show cards from regex codes :
ah displays As of hearts,
kc displays King of clubs
...
I used preg_replace() to do that in this way :
$arr = array('ah', 'kh', 'qh', ..., '3c', '2c');
$regex = '';
foreach ($arr as $i => $card)
{
$regex .= $card;
if ($i < count($arr) - 1)
$regex .= '|';
}
$message = preg_replace('#('.$regex.')#', '<img src="'.$dontknow.'.png" class="card" alt="" />', $message);
I don't know what value put in the src attribute, I want to tell to preg_replace() "when you find 'ah' you put ah.png, if it's kc then $dontknow == 'kc' etc.
Someone could be bring me some help ?

Answer 1

You can do this:
$message = preg_replace('#('.$regex.')#',
'<img src="$1.png" class="card" alt="" />', $message);

Answer 2

Use $1 reference - it is a link to a first group that PHP matched through preg_replace

Answer 3

You just need to use $n in your replacement to reference to a certain matching group (n is a number).
Since we pulled out the big guns:
Let's use preg_quote() to escape regex reserved characters in your array
PHP has a great set of function to juggle with arrays, let's use implode() instead of that ugly loop
From the comments, I realised that you need to add word boundaries \b to prevent false matches like yeah being replaced to ye<img...>. See this demo
Code:
$message = 'foo qh bar';
$arr = array('ah', 'kh', 'qh', '3c', '2c');
$escaped_arr = array_map(function($v){
return preg_quote($v, '#');
}, $arr); // Anonymous function requires PHP 5.3+
$message = preg_replace('#\b('.implode('|', $escaped_arr).')\b#', '<img src="$1.png" class="card" alt="" />', $message);
echo $message;
Online demo

Answer 4

You don't need that for loop. Here's a slightly improved version with the correct regex.
$arr = array('ah', 'kh', 'qh', ..., '3c', '2c');
$message = preg_replace('/('. implode('|'. $regex) .')/is', '<img src="$1.png" class="card" alt="" />', $message);

Answer 5

You should improve your 'markers' indicating the playing cards, by adding a special character (like # in the following example) to them. This will protect you from inadvertently changing other text passages:
$arr = array('ah', 'kh', 'qh', 'ac', '3c', '2c');
$txt = 'This is a line with cards #ah and #qh but with a potential head-ache.';
$rx = '##('.join('|',$arr).')#';
echo preg_replace($rx,"<img src=$1.jpg>",$txt);