sub foo {
  # get singular hash reference with any number of key/value pairs
  my $params = shift @_; # or alternatively, my $params = $_[0]
  
  # some may want to dereference (I usually don't)

  my %params = %$params;

  return;
}

# to call:

foo( {'key1' => 'val1', 'key2' => 'val2', 'key3' => 'val3' });

# or without braces,

foo( 'key1' => 'val1',  'key2' => 'val2', 'key3' => 'val3' );