rename 's/foo/bar; $_ = $was if -e' *foo*

  find . -print | rename 's/readme/README/i'

  find . -print | rename 's/$/.old/ if -M $_ > 0.5'

  find . -name '*,v' -print | \
    rename 's#(.*)/#$1/RCS#, $x{$1}++ || mkdir("$1/RCS", 0777)'