How do you perform a preg_match where the pattern is an array, in php?

Question

I have an array full of patterns that I need matched. Any way to do that, other than a for() loop? Im trying to do it in the least CPU intensive way, since I will be doing dozens of these every minute.

Real world example is, Im building a link status checker, which will check links to various online video sites, to ensure that the videos are still live. Each domain has several "dead keywords", if these are found in the html of a page, that means the file was deleted. These are stored in the array. I need to match the contents pf the array, against the html output of the page.

Answer 1

First of all, if you literally are only doing dozens every minute, then I wouldn't worry terribly about the performance in this case. These matches are pretty quick, and I don't think you're going to have a performance problem by iterating through your patterns array and calling preg_match separately like this:

$matches = false;
foreach ($pattern_array as $pattern)
{
  if (preg_match($pattern, $page))
  {
    $matches = true;
  } 
}

You can indeed combine all the patterns into one using the or operator like some people are suggesting, but don't just slap them together with a |. This will break badly if any of your patterns contain the or operator.

I would recommend at least grouping your patterns using parenthesis like:

foreach ($patterns as $pattern)
{
  $grouped_patterns[] = "(" . $pattern . ")";
}
$master_pattern = implode($grouped_patterns, "|");

But... I'm not really sure if this ends up being faster. Something has to loop through them, whether it's the preg_match or PHP. If I had to guess I'd guess that individual matches would be close to as fast and easier to read and maintain.

Lastly, if performance is what you're looking for here, I think the most important thing to do is pull out the non regex matches into a simple "string contains" check. I would imagine that some of your checks must be simple string checks like looking to see if "This Site is Closed" is on the page.

So doing this:

foreach ($strings_to_match as $string_to_match)
{
  if (strpos($page, $string_to_match) !== false))
  {
    // etc.
    break;
  }
}
foreach ($pattern_array as $pattern)
{
  if (preg_match($pattern, $page))
  {
    // etc.
    break;
  } 
}

and avoiding as many preg_match() as possible is probably going to be your best gain. strpos() is a lot faster than preg_match().