正则表达式替换特定标记内所有出现的单个字符

Question

I would like to know if a single set of regex search/replace patterns could be used to replace all occurrences of a specific character inside a string contained within 2 tokens.

For example, is it possible to replace all periods with spaces for the text between TOKEN1 & TOKEN2 as in the example below?

So that:

TOKEN1:Run.Spot.run:TOKEN2

is changed to:

TOKEN1:Run Spot run:TOKEN2

NOTE: The regular expression would need to be capable of replacing any number of periods within any text, and not just the specific pattern above.

I ask this question more for my personal knowledge, as it is something I have wanted to do quite a few times in the past with various regex implementations. In this particular case, however, the regex would be in php.

I am not interested in php workarounds as I know how to do that. I am trying to expand my knowledge of regex.

Thanks

Answer 1

A way to do this:

$pattern = '~(?:TOKEN1:|\G(?<!^))(?:[^:.]+|:(?!TOKEN2))*\K\.~';
$replacement = ' ';
$subject = 'TOKEN1:Run.Spot.run:TOKEN2';
$result = preg_replace($pattern, $replacement, $subject);

pattern details:

~                  # pattern delimiter
(?:                # open a non capturing group
    TOKEN1:        # TOKEN1:
  |                # OR
    \G(?<!^)       # a contiguous match but not at the start of the string
)                  # close the non capturing group
(?:                # open a non capturing group
    [^:.]+         # all that is not the first character of :TOKEN2 or the searched character
  |                # OR
    :(?!TOKEN2)    # The first character of :TOKEN2 not followed by the other characters
)*                 # repeat the non capturing group zero or more times
\K                 # reset the match
\.                 # the searched character
~                  # delimiter

The idea is to use \G to force each match to be TOKEN1: or a match contiguous with the precedent match.

Notice: the default behavior is like an html tag (it is always open until it is closed). If :TOKEN2 is not found all the \. characters will be replaced after TOKEN1:.