[Canberra-pm] how to tell if a library is available?

[Paul Fenwick]

G'day Kim / CPM,

Kim Holburn wrote:

> eval "use Text::Autoformat" ;
> if (!$@) {
>    use Text::Autoformat ;
>    ....

Aha!  You've been caught by the fact that "use" statements happen at 
compile-time, and not run-time.  This means that a "use" inside an if 
structure gets executed before perl even looks at the conditional.

The string eval effectively delays loading of the module to run-time, as 
well as capturing the error if the module can't be find.

Note that the eval *will* load the module if it's available.  If it's not, 
it sets $@ with the reason why it could not be loaded (usually because it's 
not installed).

This means your code can be written as:

eval "use Text::Autoformat";

if ($@) {
	print "Drat, Text::Autoformat not available";
} else {
	print "We have Text::Autoformat loaded";
}

All of this assumes that you want to use the module if it's available, which 
is usually the case.

> If I don't have the use statement I get lots of other errors (using -w).

I can only guess these are genuine warnings that relate to the rest of the 
code, but not the specific task of loading a module.

Cheerio,

	Paul

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