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Why does this regex capture give 2 matches?

I don't know why there are two matches found outside of the input using this regex when I was only expecting 1 match.

preg_match(/_(\d(-\d){0,3})\./,$str,$matches);

in this string format name_A-B-C-D.ext

.

I would expect to get one match:

Example A
[0] => name_A-B-C-D.ext  
[1] => A-B-C-D

Example B
[0] => name_A-B-C.ext  
[1] => A-B-C

But this is the result:

Example A
[0] => name_A-B-C-D.ext  
[1] => A-B-C-D
[2] => -D

Example B
[0] => name_A-B-C.ext  
[1] => A-B-C
[2] => -C

I want to write A

before D

if it is preceded by a hyphen. This code can be used and I can just ignore the second match, but I would like to know why its there. I can only assume that it has something to do with my two capture groups. Where is my mistake?

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3 answers


Yes, you get two snapshots because there are two capture groups in your regex.

To avoid unwanted capture, you can use a non-capture group (?:...)

:



/_(\d(?:-\d){0,3})\./
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I can only assume that it has something to do with my two capture groups.

Your guess is correct



Where is my mistake?

No errors, everything behaves as expected.

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You have groups in your RE, so you get 2 matches. What's amazing? Each pair of brackets represents a group.

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