XML::Twig is one of the many things that keeps me using Perl. (It's one of the modules my personal 'M.pm' module loads -- 'M.pm' so I can do perl -MM -lwe ....) So, thanks again, mirod.
The first thing that came to mind was:
perl -MXML::Twig -E 'XML::Twig->new( twig_handlers => { _all_ => sub { say $_->xpath } })->parsefile(shift)'
...which isn't so different from what you wrote. But, the following has the benefit of not requiring the loading of the entire file (correct?):
perl -MXML::Twig -E 'XML::Twig->new( start_tag_handlers => { _all_ => sub { say $_->xpath } })->parsefile(shift)'