I'd like to highlight some things: Firstly, embedding packages in a script, or having multiple packages in the same file are not unusual. One can even use the technique of embedded-package in production for practical reason.

So is there anyway to define a separately named package and not put it in another file?

Yes, exactly as you give in your example. Just put the package PackageName; line to define a new package scope, or switch back to a previously defined package.

#!/usr/bin/perl
use strict;
use warnings;
use CGI;

# this is by default in package main scope

package TempConverter;

# define necessary stuff for TempConverter
# and start its package scope

# you can even do this, to....
package CGI;
# ...extend the CGI package, but this is not
# recommended

package TempConverter;
# back in TempConverter scope and add
# something you need

package main;
# now in main scope, ready for action!
# the safest place to do things
[download]

It's important to pay attention about the declaration/definition order to avoid unexpected result.

How do I "use" it in the main scriptlet file?

There are some ways:

• By using fully qualified name on the resources you'd like to use (subroutines & package variables), that is prefixing the symbol name with package name and '::'. As shown by GrandFather, you say my_temp_convert::set_temp(32) instead of set_temp(32).

• Aliasing the symbol tables you're going to access so you don't have to fully qualify the symbol name. kyle has shown some examples.

  package main;
  *set_scale = \&my_temp_convert::set_scale;
  set_scale(1);
  [download]

• Make the package as a class by defining a construct, e.g. new(). kyle also mentions about this.

  sub new { bless {} }
  sub set_scale {
    my $self = shift;
    $curr_scale = shift;
  }
  
  # later.....
  package main;
  my $temp = my_temp_convert->new;
  $temp->set_scale(1);
  [download]

• Since you're using Exporter in my_temp_convert package, you can import the symbol tables into main package. (kyle uses an alternative syntax to do this).

  package main;
  my_temp_convert->import;
  set_scale(1)
  [download]

• Should the my_temp_convert package doesn't use Exporter module, but you still want to access the symbols without fully qualifying their names, and you don't want to alias them one by one, then you can alias them all at once.

  package main;
  no strict 'refs'; # this is necessary
  for my $sym (keys %my_temp_convert::) {
    *{"::$sym"} = *{"my_temp_convert::$sym"};
  }
  set_scale(1);
  [download]

Note: I remember I once used a single assignment to basically do the same with what for does above, but I can't find references about that in the official docs anymore. The assignment below,

*main:: = *my_temp_convert::;
[download]

gives me a "Modification of a read-only value" fatal exception. I'm not sure if that's the correct syntax I used or thing has changed. Any monk knows what happens?

Don't focus on the triviality of my "temperature convert" package

Well, at least use valid syntax even for example. Or, state that your example uses pseudo code. Please remember that we're using PerlMonks to help each other. Supplying some example code indicates that you put some efforts and help others to help you. Things in <code></code> tags are downloadable, and allow other people to try your code. So I would appreciate if you wrote,

sub set_scale{$curr_scale=shift}
sub set_temp($){
  #convert to C if needed, and store in "curtmp"
}
[download]

instead of

sub set_scale{ curr_scale=shift}
sub set_temp($){#convert to C if needed, and store in "curtmp"}
[download]

People will try to work based on your code you supply to closely match the context of your problem so it's prefered if your code is syntatically correct (unless the problem is with the syntax itself), so people don't have to modify a lot of things.

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