Best way to check for installed module

jmay has asked for the wisdom of the Perl Monks concerning the following question:

Scenario: I want to determine if My::Module is installed on the current system, so I can have conditional behavior based on whether it is there or not. This is not a strict dependency, so I don't want the standard behavior of "use My::Module". So far I've come up with this:

if (defined eval "require My::Module") {
    print "all's well\n";
} else {
    print "nope, figure out a workaround\n";
}
[download]

But is this likely to be too harsh? There are other conditions that could cause require to fail besides "Can't locate My/Module.pm in xxx".

Suggestions appreciated,

-Jason

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Re: Best way to check for installed module by ehdonhon (Curate) on Apr 04, 2002 at 19:43 UTC
See Use a module only if it is available.	[reply]
Re: Best way to check for installed module by extremely (Priest) on Apr 04, 2002 at 20:47 UTC
The canonical way from the Cookbook is simply: `BEGIN { unless (eval "require MyModule") { warn "Eeek! no MyModule: $@"; } } BEGIN { unless (eval "use MyModule") { warn "Eeek! no MyModule: $@"; } }` [download] -- $you = new YOU; honk() if $you->love(perl)	[reply] [d/l]
Re: Best way to check for installed module by Juerd (Abbot) on Apr 04, 2002 at 19:44 UTC
if (defined eval "require My::Module") { If the name of the module is constant, you should use eval BLOCK instead of eval STRING: `if (defined eval { require My::Module }) {` [download] Apart from that, your approach is very common, and I have yet to see a better way to do it. U28geW91IGNhbiBhbGwgcm90MTMgY W5kIHBhY2soKS4gQnV0IGRvIHlvdS ByZWNvZ25pc2UgQmFzZTY0IHdoZW4 geW91IHNlZSBpdD8gIC0tIEp1ZXJk	[reply] [d/l]
Re: Re: Best way to check for installed module by extremely (Priest) on Apr 04, 2002 at 20:40 UTC
The block form may be safe with require but don't fall into that trap and use the block form with "use Module"; since the perl compiler will spot the use xxx long before the wrapping code is actually executed... -- $you = new YOU; honk() if $you->love(perl)	[reply]
Re: Best way to check for installed module by maverick (Curate) on Apr 04, 2002 at 19:47 UTC
There are other things that could make the eval fail, syntax errors, missing the 1; at the bottom of the pm...but in each of those cases you'd probably still want to treat it as if you "didn't have it". You couldn't use a broken module anyways... :) As for the actually technique... That's probably what I'd use, I can't seem to think of another way off hand. /\/\averick OmG! They killed tilly! You bleep!!!	[reply]
Re: Best way to check for installed module by DigitalKitty (Parson) on Apr 04, 2002 at 20:57 UTC
Hi Monks, One very simple method uses the following one-liner: `perl -e "use IO::Socket"` [download] Thanks, -DK	[reply] [d/l]
Re: Re: Best way to check for installed module by count0 (Friar) on Apr 05, 2002 at 14:06 UTC
Or similarly, as I do: `perl -MModule::InQuestion -e '1'`. /me hugs perlrun ;) Btw, you can even check $? (in bash) programatically to see if it was successful. </my 1.5 cents>	[reply] [d/l]