% perl -de 1

Loading DB routines from perl5db.pl version 1.23
Editor support available.

Enter h or `h h' for help, or `man perldebug' for more help.

main::(-e:1):   1
  DB<1> use CGI 'param'

  DB<2> @x = param( 'foo' )

  DB<3> @y = scalar param( 'foo' )

  DB<4> x @x
  empty array
  DB<5> x @y
0  undef
  DB<6> p scalar @x
0
  DB<7> p scalar @y
1