正则表达式在PHP中没有正确评估

Question

I'm having a problem with PHP regular expression matching.

The problem I'm trying to solve is I that I need to get a decimal value from a string. The expression needs to meet all the following (all dollar signs optional):

($)1234.56
($)1,234.56
($)1.00
($)10
($).49
($)1,234,567.32
($)1,234,567

After finding some wonderful examples online, I was able to Frankentstein this expression together:

/(?:^|\s|\$)([1-9](?:\d*|(?:\d{0,2})(?:,\d{3})*)(?:\.\d*[0-9])?|0?\.\d*[0-9]|0)(?:\s|$)/

If you use this preg_match tester on solmetra, using the above pattern and the test string 'per unit price $19198.01 hey!' you will will get the following result:

Array
(
    [0] => $19198.01 
    [1] => 19198.01
)

Which is great - it's exactly what I need!

However, when I run the below code in PHP 5.3.10, I get null as an output for matches using this pattern string:

Code:

  $pattern = '/(?:^|\s|\$)([1-9](?:\d*|(?:\d{0,2})(?:,\d{3})*)(?:\.\d*[0-9])?|0?\.\d*[0-9]|0)(?:\s|$)/';
  $subject = 'per unit price $19198.01 hey!';
  $matches = preg_match($pattern,$subject);                
  var_dump($matches[0]); //dumps "null"

I'm sure I'm doing something wrong, but I just can't see it.

Any help would be greatly appreciated.

Environment:

PHP  5.3.10
Apache 2.2.21
Windows 2008 Server

Answer 1

Your error is just in the function usage:

 $matches = preg_match($pattern,$subject);   

What you are actually getting there is:

 $booleanresult = ...

But you need the third param to preg_match for the actual outcome:

 $bool = preg_match($pattern, $subject, $matches);   

And voila, your regex does actually work. I'd additionally recommend the /x flag to make it a bit more readable though.