You can use "do" as davidrw has already said. But a more scalable approach might be to create a real module and to use that in all of your other programs. A simple module that just contains a few functions would look like this.

package My::Module::Name;

require Exporter;
our @ISA = qw(Exporter);
our @EXPORT_OK = qw(some_function another_function);

sub some_function {
  print "This is some function\n";
}

sub another_function {
  print "This is another function\";
}

1;
[download]

So it's really not as complex as many people seem to think.