On second glance, I'm not sure what you're trying to do with the regex, but if my above comments gets you on your way to your solution, perhaps we won't need to delve into the problems with the regex above as written.

$/  =  q#(\w)#  ;  sub  sig { print scalar reverse  join  ' ',  @_  } 
+ sig
map { s$\$/\$/$\$2\$1$g && $_ } split( ' ', ",erckha rlPe erthnoa stJu
+" );
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