Trying to figure out a Regular Expression to match only 2 consecutive "#". The regex should be able to detect a match within the following examples:

Example 1) firstword ##helloworld## lastword

Example 2) ##helloworld##

I currently have ^##.*##$ but it incorrectly matches to:

###helloworld###

Or it doesn't match when there's a string before or after 2 consecutive #:

firstword ##helloworld## lastword

Any feedback welcomed!!

CodePudding user response：

You can use lookarounds like

(?<!#)##(?!#).*?(?<!#)##(?!#)

Details:

• (?<!#)##(?!#) - a ## string not immediately preceded nor followed with another # char
• .*? - any zero or more chars other than line break chars as few as possible
• (?<!#)##(?!#) - a ## string not immediately preceded nor followed with another # char