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

Jacinta Richardson jarich at perltraining.com.au
Sat Jun 14 02:40:16 PDT 2008

Kim Holburn wrote:
> I have a script which could use a library (Text::Autoformat) if it's  
> available in the current libs or if it's in the directory the script  
> is in.  I'd like a simple test to tell this before I either try and  
> use it or use a work-around.
> Is there any simple test for this?

Try using it with a string eval and then check $@.  For example:

	eval "use Foo;";
	if($@) {
	        print "Could not find Foo\n";

	eval "use Bar;";
	if($@) {
	        print "Could not find Bar: $@\n";

	print "Program completed\n";

with Foo.pm being:

	package Foo;

	print "Foo!\n";



	jarich at teddybear:/tmp$ perl test.pl
	Could not find Bar: Can't locate Bar.pm in @INC (@INC contains:
	/etc/perl /usr/local/lib/perl/5.8.8 /usr/local/share/perl/5.8.8 	
	/usr/lib/perl5 /usr/share/perl5 /usr/lib/perl/5.8
	/usr/share/perl/5.8 /usr/local/lib/site_perl
	/usr/local/lib/perl/5.8.4 /usr/local/share/perl/5.8.4 .) at
	(eval 2) line 1.
	BEGIN failed--compilation aborted at (eval 2) line 1.

	Program completed

If you choose to try to use a second module upon failing the first, 
remember to save $@ if you ever intend to use it:

	eval "use Foo;";
	if(my $E = $@) {
	        print "Could not find Foo, trying Bar\n";
		eval "use Bar;";
		# $@ has now changed!

I hope this helps.


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