@a = qw{ one two };
@b = qw{ tre for };
{
   local $" = "-";
   print "@a @b";        # one-two tre-for
}
{  local $, = "-";
   print @a, @b;         # one-two-tre-for
   local $" = ":";
   print "@a", "@b";     # one:two-tre:for
}