How to check if perl module is available? - perl

Question

I have found this:
my $rc = eval
{
require Term::ReadKey;
Term::ReadKey->import();
1;
};
if($rc)
{
# Term::ReadKey loaded and imported successfully
...
}
But that does not work for packages defined inside other modules like:
{
package Hi::Test;
}
my $rc = eval{ require Hi::Test };
$rc is false here.
How can I check that 'Hi::Test' is available?

Answer 1

I'm assuming there is actually something happening in that package, and not just an empty block.
The following code checks if there are any entries in the symbol table for that package. It's dirty, but it works as long as there are subs or package variables registered.
{
package Hi::Test;
sub foo;
}
my $rc = eval{ require Hi::Test };
if (! $rc) {
$rc = do {
no strict;
*stash = *{"Hi::Test::"};
scalar keys %stash;
}
}
print $rc;
It will print 1.

Answer 2

You want something like defined(*Hi::Test::), except that simply mentioning *Hi::Test:: creates the package.
$ perl -E'
say defined(*Hi::Test::) ? "exists" : "doesn'\''t exist";
'
exists
By using symbolic references, you avoid that problem.
$ perl -E'
{ package Hi::Test }
say defined(*{"Hi::Test::"}) ? "exists" : "doesn'\''t exist";
say defined(*{"Hi::TEST::"}) ? "exists" : "doesn'\''t exist";
'
exists
doesn't exist
Putting that code in a sub to makes things cleaner.
$ perl -E'
use strict;
use warnings;
sub test_for_package {
my ($pkg_name) = #_;
$pkg_name .= "::";
return defined(*$pkg_name);
}
{ package Hi::Test }
say test_for_package("Hi::Test") ? "exists" : "doesn'\''t exist";
say test_for_package("Hi::TEST") ? "exists" : "doesn'\''t exist";
'
exists
doesn't exist
Note that creating the package Foo::Bar::Baz also creates the packages Foo and Foo::Bar.

Answer 3

I'm a little rusty on this, but I think your require will be failing regardless - this errors:
#!/usr/bin/perl
{
package Hi::Test;
sub foo {
print "bar\n";
}
}
{
package main;
require Hi::Test;
}
This errors - it can't find it #INC (because it isn't in #INC). Both use and require specifically tell perl to "go out and find a module file"
But you can still call 'foo' with:
Hi::Test::foo();
So you can't test the loading of the module with eval nor can you check %INC .
But what you can do is check %Hi:::
use Data::Dumper;
print Dumper \%Hi::;
print Dumper \%Hi::Test::;
Which gives us:
$VAR1 = {
'Test::' => *{'Hi::Test::'}
};
$VAR1 = {
'foo' => *Hi::Test::foo
};
So we can:
print "Is loaded" if defined $Hi::{'Test::'}

Answer 4

UPDATED
I have found this clue:
my $module = *main::;
my #sub_name = split '::', $full_name;
while( each #sub_name ) {
$module = $$module{ $sub_name[$_].'::' };
}
print "Module is available" if $module;
In compare to this answer it does not create additional variable in global stash