Question

Learning regex but this one gives me a headache. I need to match a float number (with either . or , as decimal point) and it MUST end with the following characters: €/g.

Valid matches should be for example:

• 40€/g
• 43.33€/g
• 40,2€/g
• 40.2€/g
• 38.943€/g

Appreciate help..

Answer 1

The regex will look like:

\d+(?:[.,]\d+)?€/g

In Javascript, as a regex object (note that the forward slash needs to be escaped):

/\d+(?:[.,]\d+)?€\/g/

Here’s a breakdown of what each part does:

\d+  # one or more digits
(?:    # ... don't capture this group separately
 [.,] # decimal point
 \d+  # one or more digits
)?   # make the group optional
€/g  # fixed string to match

If you want to allow something like .123€/g to be valid as well, you can use:

(?=[.,]|\d)(?:\d+)?(?:[.,]\d+)?€/g

That is, both the groups of digits are optional, but at least one must be present (this uses lookahead, which is a bit more tricky).

Note that this will also match constructions like ‘word2€/g’. If you want to prevent this, start the regex with (?<=^|\s) (matches if preceded by a space or the start of the string) and end it with (?=$|\s) (matches if followed by a space or the end of the string).

Full-blown version:

(?<=^|\s)(?=[.,]|\d)(?:\d+)?(?:[.,]\d+)?€/g(?=$|\s)