The beauty of Perl is you don't have to do it any which way. TIMTOWTDI, after all.

But I think you've gotten some concepts confused. I had trouble initially with Perl's idea of packages because I was so used to Java. Java has a one-to-one relationship between a file and its namespace. The class java.lang.String has to live in a file called "String.class" in a directory hierarchy of java/lang. Perl on the other hand allows you to switch namespaces within the same file, or use a namespace that's totally unrelated to the file the code lives in.

In practice, there usually is a correspondence between a file (like Crypt/Blowfish.pm) and the namespace it uses (Crypt::Blowfish::). But this doesn't have to be. In your example for instance, I can put somesub in a separate namespace within the same file, or load a somesub that lives in a namespace totally unrelated to the file name it is defined in:

In a file called "TestFile.pm":

package Foo::Bar;

sub somesub{
    return "somesub value from package Foo::Bar!";
}

1;
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In a file called "test.pl":

use TestFile;

package Common;

sub somesub {
    my $value = 'somesub value from Common package!';
    return $value;
}

package main;

print "Back in main package.\n";

my $rv1 = Common->somesub();   # Defined just above in this file
my $rv2 = Foo::Bar->somesub(); # Found in file TestFile.pm

print "Return Value 1: $rv1\nReturn Value 2: $rv2\n";
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My point being that file names and packages are very loosely coupled in Perl. Good reading for all of this is perlmod and package.