package MyAppCommon;
use strict;

sub CommonPageStart {
  ...
}

sub CommonPageEnd {
  ...
}

1;
__END__

# and then, in your scripts
use MyAppCommon;  # use is basically like require... see the docs for 
+details
MyAppCommon::CommonPageStart(...);

# your stuff

MyAppCommon::CommonPageEnd(...);
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As for more direct reasons of why this is better:

• It makes your code more easily maintainable and extensible because your code is organized into packages, and it is namespaced (so you can easily add it to another application without worry of namespace collision, and likewise, other modules can be added to it easily without worry of namespace collision)
• It is more time-efficient. If you "do" a file, it is read off of disk and parsed with each invocation. However, when a file is "use"d or "require"d (same mechanism, mostly) it is only read off of disk and parsed/compiled once. Further references to it are just referring back to the first copy made. In a mod_perl process, for instance, this can lead to enormous speed improvements.
• For much the same reasons, it is more space-efficient. Since the file is only compiled once, the subroutines and data structures and data internal to the perl interpretter (for, say, storing the internal representation of the parsed and compiled code) are only stored once. Again, under mod_perl, this affect can be multiplied even more if your modules are pre-loaded in the parent process (before forking), as each server-process reuses the same copy (more or less) of the compiled code of the modules.
• etc

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:Wq
Not an editor command: Wq
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