Question

  x|m expr       Evals expr in list context, dumps the result or lists methods.
  p expr         Print expression (uses script's current package).

They seems identical to me,what’s different?

Also,is there any short cut like up/down arrow key in shell environment?

Answer 1

See perldoc perldebug:

p expr Same as “print {$DB::OUT} expr” in the current package. In
particular, because this is just Perl’s own “print”
function, this means that nested data structures and
objects are not dumped, unlike with the “x” command.

and

Readline Support / History in the debugger
As shipped, the only command-line history supplied is a simplistic one
that checks for leading exclamation points. However, if you install
the Term::ReadKey and Term::ReadLine modules from CPAN (such as
Term::ReadLine::Gnu, Term::ReadLine::Perl, …) you will have full
editing capabilities much like GNU readline(3) provides. Look for
these in the modules/by-module/Term directory on CPAN.