Regex to extract last elements from a list-CodePudding

I can have as input the following list: V1, V2, V3, V4, V5, V6, V7, V8, V9, V10

I would need a regex that extracts the last 3 elements from the list above. So after applying the regex the list should look like: V8, V9, V10

I have tried this regex /^.*(?=((,.*){3})$)/, it seems I'm getting close but I don't understand why when replacing with $1 I get the output duplicated.

Can anyone help me with an explanation? If I'm able to understand why this happens I should be able to correct it.

CodePudding user response：

The following regex should work

/^.*, ([^,] , [^,] , [^,] )$/

^ Match the beginning of the string
.* Match 0 or more characters, taking as many as posible
, Match a comma followed by a space
( Begin capture
[^,] Match one or more not commas
This gets repeated so we can match the last 3 elements
) End capture
$ Match end of string

CodePudding user response：

You can simply extract the last three comma-separated values using

[^\s,][^,]*(?=(?:,[^,]*){0,2}$)

See the regex demo. Details:

[^\s,] - a char other than whitespace and comma
[^,]* - any zero or more chars other than a comma
(?=(?:,[^,]*){0,2}$) - a positive lookahead that requires zero, one or two occurrences of a comma and then zero or more non-comma chars till the end of string immediately to the right of the current location.

You get you match replaced twice because of a known issue, see Why do some regex engines match .* twice in a single input string?.

CodePudding user response：

For your case, you should use ?: instead of ?=, then you will get , V8, V9, V10

([a-zA-Z0-9] (?:,\s[a-zA-Z0-9] ){2})$ will return the same without preceding comma V8, V9, V10