perl -MO=Deparse -e '$_="abcdef"; s/@{[s".."."gr]}\K$"//; print'
$_ = 'abcdef';
s[@{[s/.././rg];}\K][$"];
print $_;
-e syntax OK
  

##</code><code>##

perl -MO=Deparse -e '$_="abcdef"; s/@{[s".."."gr]}\K //; print'
$_ = 'abcdef';
s[@{[s/.././rg];}][\\K ];
print $_;
-e syntax OK