PHP - preg_match - 如何匹配以零开头的数字

Question

I am trying to use preg_match to match numbers that start with a zero to indicate an invalid input. Numbers such as 01, 0023, 00.4 are invalid; however numbers such as 0.12 are valid. The input would be a calculator entry, such as 09 * 108 + 0.19 + 4009. In this case, the expression would be invalid because of the 09.

So far my expression looks like: preg_match("/[^1-9]+0[0-9]+/", $subject)

What I tried to do was match when a zero precedes any string of digits, but is also not preceded by another string of digits. So 109 is valid, but 1+09 is invalid. However it isn't working for cases like 1 + 4009.

Answer 1

preg_match('/\b0[0-9]+(?:\.[0-9]+)?\b/', $subject)

\b for word boundary.