# OP's solution, given a different input:

$ perl -le'print $1 while "ZBBBCZZCZ" =~ /((.)\2*)/g'
Z
BBB
C
ZZ
C
Z

# jwkrahn's solution for that input:

$ perl -le'print for keys %{{"ZBBBCZZCZ" =~ /((.)\2*)/g}}'
Z
ZZ
BBB
C