Question

I was wondering if you could help me formulate a regular expression to match the following pattern?

Any arbitrary length string of numbers, which may or may not be preceded by 0x.

Answer 1

Something like this:

\b(?:0x)?\d+\b 

or this, if you want to exclude the optional '0x' from the match:

(?:(?<=\b0x)|\b)\d+\b 

The former is:

 - a word boundary - '0x', optional - decimal digits, at least one - a word boundary 

the latter would be:

 - choose   - either a position preceded by      - a word boundary      - '0x'   - or a word boundary - decimal digits, at least one - a word boundary 

The latter matches:

 - 123456 - 0x123456 

but not:

 - 0y123456 

To match hex digits (as your ‘0x’ implies), use [0-9A-Fa-f] in place of the '\d'.