# The reserved word 'sub' defines a subroutine.

# Basic subroutine with on parameter:
sub mysub {
   my $param = shift;
   #
   # Do stuff here
   return $myvalue
}
$x = mysub( "value" )

# Named parameters to subroutines:
sub named_params_example {
   my ( $arg ) = @_;
   # Use my ( $self, $arg ) = @_; if you are in object land.
   #
   say $arg->{one};
   say $arg->{two};
}
#
# Calling the above subroutine:
named_params_example({
   one => "First argument",
   two => "Second argument"
});

# Named parameters with default values:
sub named_params_with_defaults {
   my ( $arg ) = @_;
   # Use my ( $self, $arg ) = @_; if you are in object land.
   #
   # Set defaults
   #         If option given      Use options   Else
   my $one = exists $arg->{one} ? $arg->{one} : "default1";
   my $two = exists $arg->{two} ? $arg->{two} : "default2";
}
#
named_params_with_defaults({ one => "override arg 'one'" });

# Return named params from a subroutine:
sub foo {
   my $clause = 'This is a clause';
   my @param = qw/ one two thee /;
   return ({
      clause => $clause,
      params => \@param
   });
}
#
my $r = foo();
#
say "clause = [$r->{clause}]";
for my $p ( @{ $r->{params} } ) {
   say "param = [$p]";
}

# More help with Perl's fabulous perldoc command:
perldoc sub