Re: modules using things from other modules

Modules are only read from disc and stored in memeory once, no matter how many times a program or module uses them. This is tracked by the special variable %INC (documented in perlvar).

For example...

use Foo;
#%INC now contains ( 'Foo.pm' => '/absolute/path/to/Foo.pm' )

use Foo;
#perl "sees" that Foo has been loaded from that entry in %INC and proc
+eeds directly to import()
[download]

Also, see use for more details about how it works, specifically it's relationship to require

Comment on Re: modules using things from other modules Download Code

Replies are listed 'Best First'.
Re^2: modules using things from other modules by Anonymous Monk on Sep 01, 2008 at 22:37 UTC
that method and module is just one example of what I need use. So what you guys saying is that even if i use a module in my module, if it is alredy loaded it done not get loaded again? thats great news	[reply]
Re^3: modules using things from other modules by ikegami (Patriarch) on Sep 01, 2008 at 22:57 UTC
If it was loaded via `require` or `use`, yes, it is only compiled and executed the first time. It's `import` method will be called each time, allowing symbols to be exported into multiple namespaces. `# script.pl use Module1; use Module2;` [download] `# Module1.pm package Module1; BEGIN { print("Compiling Module1\n"); } use Module2; sub import { print("Module1 exporting to ". caller() . "\n"); } print("Executing Module1\n"); 1;` [download] `# Module2.pm package Module2; BEGIN { print("Compiling Module2\n"); } sub import { print("Module2 exporting to ". caller() . "\n"); } print("Executing Module2\n"); 1;` [download] `>perl script.pl Compiling Module1 Compiling Module2 Executing Module2 Module2 exporting to Module1 Executing Module1 Module1 exporting to main Module2 exporting to main` [download] `>perl script.pl \| sort Compiling Module1 --> once Compiling Module2 --> once Executing Module1 --> once Executing Module2 --> once Module1 exporting to main --> once per "use" Module2 exporting to main \ Module2 exporting to Module1 --> once per "use"` [download]	[reply] [d/l] [select]