Perl subroutines

   Like most other programming languages,  perl has subroutines, too. They are kind of strange, but still easy to learn. The handling of parameters and return values however is new: all functions get their parameters as one single flat list of scalars, and likewise they return to their caller one single flat list of scalar values. Any arrays or hashes in these call- and return-lists will collapse, losing their identities, but since  perl knows only calls by reference , this is no problem at all.

The following example  is a simple function which gets two values and returns  the sum of them:

sub add {
   my($a, $b) = @_;
   return $a + $b;
}

Note that there is no formal list of parameters. They are all passed to the function in the flat list @_. As mentioned before, there is only a call by reference, but a call by value  can be done, if the parameter list is assigned to locally defined variables using the instruction my. In  perl all functions have a return value. If the return statement is omitted, the variable $_ is automatically used. But like in C, it is not forced to use this return value. The following function is equivalent to the one just given:

sub add {
   $_[0] + $_[1];
}