check symbol table w/ dynamic name

skerr1 has asked for the wisdom of the Perl Monks concerning the following question:

Depending on what a user specifies, I want to include different perl modules (e.g. foo.pm bar.mk etc). I only want to include them if they haven't already been inclulded. So I may have a variable $module that contains the module specified. I want to do something like:

if (!defined(%$module::)) {
  eval {
    require "${module}.pm";
  }
}
[download]

Of course the above code doesn't work. Can someone help with this? Thanks,

Shannon Kerr

Comment on check symbol table w/ dynamic name Download Code

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Re: check symbol table w/ dynamic name by jwkrahn (Abbot) on Oct 17, 2006 at 04:32 UTC
The names of modules that are loaded with require or use are stored in the %INC hash so if a module is already loaded it cannot be loaded again.	[reply]
Re^2: check symbol table w/ dynamic name by skerr1 (Sexton) on Oct 17, 2006 at 04:47 UTC
This worked great. Thanks for this clean solution. So, here is what it will look like: `if (!$INC{ "$module.pm" }) { eval { require "${module}.pm"; } }` [download] Thanks for this! Shannon Kerr	[reply] [d/l]
Re^3: check symbol table w/ dynamic name by jwkrahn (Abbot) on Oct 17, 2006 at 04:51 UTC
The point is that perl already does the test when you require a module so your test is superfluous.	[reply]
Re^4: check symbol table w/ dynamic name by skerr1 (Sexton) on Oct 17, 2006 at 05:17 UTC
Re^2: check symbol table w/ dynamic name by ammon (Sexton) on Oct 17, 2006 at 18:52 UTC
if a module is already loaded it cannot be loaded again A minor nit-pick... a module can be re-loaded, if one is willing to do the requisite tomfoolery to make perl forget that it was already loaded.	[reply]
Re: check symbol table w/ dynamic name by ikegami (Patriarch) on Oct 17, 2006 at 05:15 UTC
`require` already checks if the module has already been loaded before loading it again, so the following should work: `my $module = 'Foo::Bar'; my $pm = $module; $pm =~ s{::}{/}g; $pm .= '.pm'; eval { require $pm } or die("Unable to load plugin $module: $@\n");` [download] Other solutions provided in this thread.	[reply] [d/l] [select]
Re: check symbol table w/ dynamic name by skerr1 (Sexton) on Oct 17, 2006 at 04:20 UTC
The following seems to work: `my $defd; eval ('$defd = defined(%'. $module .');'); if (!$defd)) { eval { require "${module}.pm"; } }` [download] I appreciate all ideas for this. Looking for the best solution. Thanks, Shannon Kerr	[reply] [d/l]