仅删除特定字符之间的空格

Question

I need to remove some white spaces between specific characters only. This is my data:

#1 2 5 1#
#   5 5 3#: 100% #5 55#
#554     #: 23    
#559#: 30%
#4 79#: 2 0 0#%
#473#: 20 #47  4#
#4  7  4 43 33 5 5#: 15s
#4 79#: 195%
#473#: 20 # 474#
#475#: 14.5s

I want all of the whitespaces between two # # tags, that are not separated by anything other than numbers, removed. My data should look like this:

#1251#
#553#: 100% #555#
#554#: 23    
#559#: 30%
#479#: 2 0 0#%
#473#: 20 #474#
#474433355#: 15s
#479#: 195%
#473#: 20 #474#
#475#: 14.5s

I'm currently trying to use the following regex in PHP to preg_replace those whitespaces, however, everything I've tried was unsuccessful.

(?:[#])(?:([\s])*[0-9]*)*(?:[#])

Debuggex Demo

Answer 1

This regex targets all the spaces you want. You can preg_replace them with empty strings.

(?:#|\G)\d*\K\s+(?=[\d\s]*#)

See demo

As a second option, since your lines seem to be starting with #, to avoid an imbalance building up between the #, you can also use:

(?m)(?:^#|\G)\d*\K\s+(?=[\d\s]*#)

Explanation

(?:#|\G)\d*\K\s+(?=[\d\s]*#)

• Match the regular expression below (?:#|\G)
  • Match this alternative (attempting the next alternative only if this one fails) #
    • Match the character “#” literally #
  • Or match this alternative (the entire group fails if this one fails to match) \G
    • Assert position at the start of the match attempt (the start of the string for the first attempt) \G
• Match a single character that is a “digit” (0–9 in any Unicode script) \d*
  • Between zero and unlimited times, as many times as possible, giving back as needed (greedy) *
• Keep the text matched so far out of the overall regex match \K
• Match a single character that is a “whitespace character” (any Unicode separator, tab, line feed, carriage return, vertical tab, form feed, next line) \s+
  • Between one and unlimited times, as many times as possible, giving back as needed (greedy) +
• Assert that the regex below can be matched, starting at this position (positive lookahead) (?=[\d\s]*#)
  • Match a single character present in the list below [\d\s]*
    • Between zero and unlimited times, as many times as possible, giving back as needed (greedy) *
    • A “digit” (0–9 in any Unicode script) \d
    • A “whitespace character” (any Unicode separator, tab, line feed, carriage return, vertical tab, form feed, next line) \s
  • Match the character “#” literally #