~$ perl5.20.1 -Mutf8 -wE 'say "abc" =~ s’b’x’r'
axc
~$ perl5.18.1 -Mutf8 -wE 'say "abc" =~ s’b’x’r'
Substitution replacement not terminated at -e line 1.
[$?: 255]
~$ perl5.18.1 -Mutf8 -wE 'say "abc" =~ s’b’’x’r'
axc