Trying to find the regex to find the last character of the string

CodePudding user response：

\b(?!\w*(\w)(?=\w*\1\b))\w \b

Test on regex101 here

This regex uses a positive lookahead inside a negative lookahead.
The positive lookahead detects characters that match the last character.
The negative lookahead rejects if such 1 was found.

CodePudding user response：

You can match the following regular expression.

(?i)(?<!\w)(?!\w*(\w)\w*\1\b)\w 

Demo

The expression can be broken down as follows.

(?i)      # assert matches are case-independent
(?<!\w)   # negative lookbehind asserts that the previous character is not
          # a word character
(?!       # begin negative lookahead
  \w*     # match zero or more word characters
  (\w)    # match a word character and save to it to capture group 1 
  \w*     # match zero or more word characters
  \1\b    # match the content of capture group 1 followed by a word boundary
)         # end negative lookahead
\w        # match one or more characters