PHP website data mining Preg_Match Undefined Offset - php

Question

I'm working on a PHP project for school. The task is to build a website to grab and analyze data from another website. I have the framework set up, and I am able to grab certain data from the desired site, but I can't seem to get the syntax right for other data that I need to obtain.
For example, the site that I am currently analyzing is a page for a specific item returned from a search of Amazon.com (e.g. search amazon.com for "iPad" and pick the first result). I am able to grab the title of the product's page, but I need to grab the review count and the price, and therein lies the issue. I'm using preg_match to get the title (works fine), but I'm not able to get the reviews nor the price. I continue to get the Undefined Offset error, which I've discovered means that there is nothing being returned that matches the given criterion. Simply checking to see whether something has been returned will not help me, since I need to obtain these data for my analysis. The 's that I'm trying to mine are unique on the page, so there is only one instance of each.
The Page Source for my product page contains the following snippits of HTML that I need to grab. (The website can, and needs to be able to handle, anything, but for this example, I searched "iPad").
<span id="priceblock_ourprice" class="a-size-medium a-color-price">$397.74</span>
I need the 397.74.
<span id="acrCustomerReviewText" class="a-size-base">1,752 customer reviews</span>
I need the 1,752.
I've tried all combinations of escape characters, wildcards, etc., but I can't seem to get beyond the Undefined Offset error. An example of my code is as follows where $link is the URL, and $f is an empty array in which I want to store the result (Note: There is NOT a space after the '<' in "< span..." It just erased everything up to the "...(.*)..." when I typed it as "< span..." without the space):
preg_match("#\< span id\=\"priceblock\_ourprice\" class\=\"a\-size\-medium a\-color\-price\"\>(.*)\<\/span\>#", file_get_contents($link), $f);
$price=$f[1]; //Offset error occurs on this line
echo $price;
Please help. I've been beating my head against this for the past two days now. I'm hoping I'm just doing something stupid. This is my first experience with preg_match and data mining. Thank you much in advanced for your time and assistance.

Answer 1

Code
As stated by #cabellicar123, you shouldn't use regex with html.
I believe what you are looking for is strpos() and substr(). It should look something like this:
function get_content($string, $begintag, $endtag) {
if (strpos($string, $begintag) !== False) {
$location = strpos($string, $begintag) + strlen($begintag);
$leftover = substr($string, $location);
$contents = substr($leftover, 0, strpos($leftover, $endtag));
return $contents;
}
}
// Usage (Change the variables):
$str = file_get_contents('http://www.amazon.com/OLB3-Official-League-Recreational-Ball/dp/B004KOBRMC/');
$beg = '<b class="priceLarge">$';
$end = '</b>';
get_content($str, $beg, $end);
I've provided a working example which would return the price of the object on the page, in this case, the price of a rawlings baseball.
Explanation
I'll go through the code, line by line, and explain every piece.
function get_content($string, $begintag, $endtag)
$string is the string being searched through (in this case an amazon page), $begintag is the opening tag of the element being searched for, and $closetag is the closing tag of that element. NOTE: This will only use the first instance of the opening tag, more than that will be ignored.
if (strpos($string, $begintag) !== False)
Checks if the beginning tag actually exists. Note the !== False; that's because strpos can return 0, which evaluates to False.
$location = strpos($string, $begintag) + strlen($begintag);
strpos() will return the first instance of $begintag in $string, therefore the length of the $begintag must be added to the strpos() to get the location of the end of $begintag.
$leftover = substr($string, $location);
Now that we have the $location of the opening tag, we need to narrow the $string down by setting $leftover to the part of the $string after $location.
$contents = substr($leftover, 0, strpos($leftover, $endtag));
This gets the position of the $endtag in $leftover, and stores everything before that $endtag in $contents.
As for the last few lines of code, they are specific to this example and just need to be changed to fit the circumstances.