Quick Tip: Perl Packages

If you have a piece of standard code that you use in a large amount of pages, you can store it in a seperate file and call it from wherever you need it.

Example:

Create a file called foo.pm in your script directory containing:


package foo;sub bar {
my ($firstname, $surname) = @_;
print "$firstname $surname\n";
}1;

The code you want to execute should be put in a subroutine, as in 'bar' above. You can have as many subroutines as you want, but the file should always start with 'package your_package_name;' and end with '1;'

The external code is called from your main script by telling Perl once at the start of the script that you want to 'use' the new package, and then using the syntax


your_package_name::subroutine_name("parameter1","parameter2","etc");

to actually execute the code. An example for the above package would be


#!/usr/bin/perluse foo;
foo::bar("John","Smith");
exit;

This would simply print "John Smith", having passed the parameters 'John' and 'Smith', which is pretty pointless in itself, but things get more interesting as the code gets more complex.

For instance, I use this technique all the time to generate navigation bars. I pass the name of the calling page to the package, which uses it to generate the navbar but with the current page highlighted on it in some way. The benefit is that you only have a single piece of navbar code to maintain, and any changes you make in it will affect the whole site. (Cascading NavBars anyone?)

You could also use it to generate a standard page footer, but with page-specific taglines at the bottom, or to generate whole <head> sections of HTML with the one command passing the title, kw and desc as parameters.

Quick Tip: Perl Packages

Using them to re-use common coding

sugarkane

han solo

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sugarkane

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