Namespace after forking()+eval()ing providing unexpected results

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

Greetings all,
I'm having a bit of trouble with a piece of code of mine. It works kinda like this:
I have two programmes, Launcher and Code. There are two modules, LaunchMod.pm and CodeMod.pm. Straightforward, right? Good. So:
Launcher loads Code from a text file, and passes it in a single string variable to LaunchMod.pm, which then does a little:

unless(fork) { eval($code) || die("Doh - $@\n"); }
[download]

Inside Code is:

use strict;
use vars qw($me);
use CodeMod;
$me = "Bob";
&CodeMod::MySub;
[download]

And inside CodeMod::MySub is a line or two that, very simply (for testing purposes) prints out the contents of $main::me. Only problem is - it doesn't.
The above says that $main::me is undefined. If I don't use LaunchMod.pm to fork/eval, and instead put that same fork/eval code inside Launch itself, everything is hunky-dory.
Obviously I'm setting up the namespace wrong, but I'm just not understanding where... Whether it forks inside the main code (Launch) or off in its module, I don't see how that can affect the eval()ed code like this...
Help?

JP,
-- Alexander Widdlemouse undid his bellybutton and his bum dropped off --

Comment on Namespace after forking()+eval()ing providing unexpected results Select or Download Code

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Re: Namespace after forking()+eval()ing providing unexpected results by chipmunk (Parson) on Jan 23, 2002 at 10:13 UTC
It's hard to say without seeing some more of the code, but I note that eval executes the string within the current package. Thus, I suspect your problem is that LaunchMod starts with `package LaunchMod;`, and the code inside the eval is executed inside the LaunchMod package, setting $LaunchMod::me rather than $main::me. You can fix this by specifying the appropriate package somewhere... The Code file could start with `package main;`, or you could stick `"package main;"` onto the front of $code before evalling it. It may also be worth considering doing away with the use of globals altogether, passing $me into &CodeMod::MySub rather than depending on it being in a specific package.	[reply] [d/l] [select]
Re: Re: Namespace after forking()+eval()ing providing unexpected results by JPaul (Hermit) on Jan 23, 2002 at 20:32 UTC
That makes lots of sense. I couldn't understand why if the fork/eval was out in LaunchMod.pm it wouldn't work, yet it would in Launcher itself - I saw only that it was doing the same code in two different places, the 'package' declaration didn't hit me... The 'package main;' makes the code work as I want it to, so I'm quite happy. The code example given is, as you can imagine, greatly simplified from the original software - where I'm using a number of globals to relate back and forth between Code and CodeMod.pm, as there are a lot of routines that use these globals - and I began to feel that passing three vars to one sub, which then distributes that to a bunch more, collects the results... and passes it all back? It just started getting really ugly... My thanks Chipmunk, JP -- Alexander Widdlemouse undid his bellybutton and his bum dropped off --	[reply]
Re: Namespace after forking()+eval()ing providing unexpected results by perrin (Chancellor) on Jan 23, 2002 at 20:22 UTC
This is actually pretty simple. When you eval() code, you do it in the context of the current package. When you say `use vars qw($me)` in the code above from within the LaunchMod package, you are talking about LaunchMod::me, not main::me.	[reply] [d/l]


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