Matching for math equations using PHP

I'm trying to write a preg_match for math equations, but for some reason when I print_r it nothing is showing up. I'm not sure what I'm doing wrong.

$text = "22/7";
preg_match("~([0-9]+([+\-*x]|(?:plus|add|minus|subtract|divide|time|multiply)(?:es|s)?(?: by)?)(?: )?[0-9]+)(((([+\-*x]|plus|add|minus|subtract|divide|time|multiply)(?:es|s)?(?: by)?)(?: )?([0-9]+))+)?~", $text, $match);
print_r($match);

Solution

The Original Problem

The problem was that there was no divide symbol present in the character group:

[+\-*x]

And should be changed to:

[+*x/-]

Enhancement

Having a further look into your regex, I wanted to see whether I could simplify it a little bit, while also adding functionality. I came up with this:

^((-?\d+(?:\.\d+)?)(?:[*+/^eE-]| (?:to the power of|plus|add|minus|subtract|divided?|times|multipl(?:y|ied))(?: by)?)(?: )?)(?1)*(?2)$

See the demo

I've added:

floating point numbers, (1.58-0.58)
optional minus numbers, (2*-4)
to the power of, (2^8)
the scientific notation (9e100)
a recursive pattern (2^8*10-9)

I'm glad you're using PHP - using the PCRE regex engine, you can do some pretty cool stuff.

Breakdown:

(-?\d+(?:\.\d+)?) - capture an optional minus, followed by a digit, followed by an optional dot and more digits (minus and floating point additions)
[*+/^eE-] - any character in this group (scientific notation, to the power of addition)
(?:to the power of|plus|add|minus|subtract|divided?|times|multipl(?:y|ied))(?: by)? - any group in this (added "to the power of")
(?1)*(?2) - Recurse group 1's regex (the entire of the pattern before it) as many times as possible, then recurse group 2's regex (the digit section), to always end on a number (recursive pattern)