Re: Conditionally faking a module

[bobf]

in reply to Conditionally faking a module

If you want to run some code if a module isn't installed, just test the use statement for failure:

eval "use Cava::Pack" 
 or do { 
  # your code goes here
};

Super Search will find several threads on this topic, including Auto install of a perl package if 'use' statement fails.

[wanna_code_perl]

Unfortunately, your example doesn't work:

eval "use Cava::Pack" or do {
    die "Using faked out Cava::Pack\n";
}

I see the "Using faked out Cava::Pack" message on both Linux and Win32 (where Cava::Pack is indeed available).

[bobf]

Apparently it may not always work, as I learned when I researched this further (see RE: Checking to see if a particular Module is installed). merlyn's response was to use the following:

eval 'require GD';
if ($@) {
  # problems with GD, fall back to non-GD
} else {
  # we have GD, go for it!
}

although there appears to be some caveats to that approach.

If you are open to using other modules to do the check, you could look into ExtUtils::Installed and Module::Load::Conditional.

See also a recent thread on this topic: Check if module is installed.

[Anonymous Monk]

That is the reason for a true value, 1

eval "use Cava::Pack; 1" or die "Oh noes! $@";
eval "use HOW::Cava::Pack; 1" or die "HOW!?! $@";
__END__
HOW!?! Can't locate HOW/Cava/Pack.pm in @INC (@INC contains: C:/perl/5
+.10.1/lib/MSWin32-x86-multi-thread C:/perl/5.10.1/lib C:/perl/site/5.
+10.1/lib/MSWin32-x86-multi-thread C:/perl/site/5.10.1/lib .) at (eval
+ 2) line 1.
BEGIN failed--compilation aborted at (eval 2) line 1.

Hmm, I don't recall installing Cava::Pack :)

[ikegami]

The code being executed by eval ("") returns nothing (()), which is indistinguishable from the value eval returns on failure.

You need

eval "use Cava::Pack; 1"