How do I repeat a capturing group?

问题

I have an input string that looks something like this:

HLI6Ch60000Ch500C0Ch46400Ch30000Ch21888Ch10E79CS07LCU3Ch37880Ch27800Ch16480CS8CA00000000000000000000

Now I don't care about the part that follows the last letter A, it'll always be A and exactly 20 numbers that are of no use to me. I do, however, need the part before the last letter A, and ideally, I'd need it to be separated into two different captures, just like this:

1: HLI6Ch60000Ch500C0Ch46400Ch30000Ch21888Ch10E79CS07
2: LCU3Ch37880Ch27800Ch16480CS8C

The only way to identify these matches is that they end with characters CS followed by two hexadecimal characters. I thought that a regular expression like (.+?CS.{2})+ (or (.+?CS[[:xdigit:]]{2})+) would do the job but when tried on www.regex101.com, it only captures the last group and gives the following warning:

Note: A repeated capturing group will only capture the last iteration. Put a capturing group around the repeated group to capture all iterations or use a non-capturing group instead if you're not interested in the data

Which I thought suggests that I should use regular expression like ((.+?CS.{2})+) instead and I mean – sure, now I get two captures, but they look like this:

1: HLI6Ch60000Ch500C0Ch46400Ch30000Ch21888Ch10E79CS07LCU3Ch37880Ch27800Ch16480CS8C
2: LCU3Ch37880Ch27800Ch16480CS8C

Meaning the first one is… slightly longer than I'd like it to be. If it helps in any way, I should point out that the final regular expression will be part of an iOS application so an instance of NSRegularExpression class will be used – not sure if that's a helpful information at all, it's just that I know that NSRegularExpression doesn't support every part of the world of regular expressions.

回答1:

Change your regex to,

(.+?CS[[:xdigit:]]{2})

DEMO

You don't need to put the regex inside another capturing group and make it to repeat one or more times. Just print the group index 1 to get your desired output.

回答2:

(.+?CS.{2})

You can direclty use this.See demo.Grab the group or capture.

https://regex101.com/r/vD5iH9/68

回答3:

It doesn't seem like you need a capturing group at all:

(?:(?!CS[0-9A-F]{2}).)+CS[0-9A-F]{2}

will match all strings that end in CS + 2 hex digits.

Test it live on regex101.com.

Explanation:

(?:                # Start a group.
 (?!CS[0-9A-F]{2}) # Make sure we can't match CSff here,
 .                 # if so, match any character.
)+                 # Do this at least once.
CS[0-9A-F]{2}      # Then match CSff.

来源：https://stackoverflow.com/questions/28318016/how-do-i-repeat-a-capturing-group

标签

ios

regex

nsregularexpression