正则表达式字符串零或更多

Question

I have follow Regex:

(.*?)( EUR)\1*

and on String 2 mm; EUR 2 mm; EUR it matches 2mm; and EUR but the String 2 mm; matches nothing!?

But why ? I thought the * meant zero or more times? Can you help me? Thank you!

Answer 1

It would have been a better approach to tell what result you want.

If you want a Regex to match "2 mm; EUR" or "2 mm;", it implies that you want to match a string starting with some kind of number (might be a millimiter length? something like that), ending with a ";" and eventually followed by the string " EUR".

If it is what you want, your regex should have a ";" inside and mark EUR with a "?" (0 or 1)

([\n]+ .*?);( EUR)?

Answer 2

The following regex will match both cases, 2 mm; EUR 2 mm; EUR as well as 2 mm;

(.*?;\s)(EUR)|(.*;)

Example

Answer 3

Yes you are right * means 'zero or more times'. What you don't seem to understand is \\1 . It means 'the content captured by the first caturing group.

Your regular expression (.*?)( EUR)\\1* means therefore:

any string, followed by the four letters EUR (with a space), followed by zero or more times the start of the string.

If the string is 2 mm; EUR2 mm;2 mm; 2 mm; EUR2 mm;2 mm; , (.*?) will match 2 mm; , ( EUR) will match EUR , and \\1* will match 2 mm;2 mm; .

Now that you understand your error, you will find more easily the correct expression. Just remove \\1 .

(.*?)( EUR)*

will match anything, followed be zero or more times EUR .

^(.*?)( EUR.*)?$

will match anything before ' EUR', or the whole string if it is missing. Notice that we added the start and end marks to make sure the whole string is captured when there is no EUR.