The good news is that this will mostly work, and I can add several things to the list of stuff I no longer have to worry about.

The bad news is I have to add new code to any module that needs to load MIBs. The new code is as follows:

@DIRS = `ls -1d /usr/local/share/snmp/mibs/TEMP/*`;
foreach $dir ( @DIRS ) {
        chomp $dir;
        &SNMP::addMibDirs("$dir");
}
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1. I don't have to modify environment variables. This is good because if $ENV{MIBDIRS} is previously unset, you have to find out where the site-wide MIBs are stored. While this is usually predictable, I'd rather not worry about it at all.
2. I don't have to modify environment variables. By adding the package's own base MIB directory to the config file, the change can be made effective site-wide (using the config file in /etc) without worrying about users' various shells, changing their environments, etc.
3. I can actually eliminate a config item I used to have in the code that kept track of the location of the site-wide MIBs that come with Net-SNMP. Again, less to worry about.
4. In the course of investigating this, I've discovered the proper use of the &SNMP::loadModules() function AND I've learned enough about duplicate MIB detection that the package's own code will be a lot leaner and the post-install script can do a lot more to detect duplicates (thus avoiding several really annoying MIB problems I've had before).

Anyway, I want to thank all those who offered suggestions. Hopefully this will be the last time I have to worry about this. :-D

--Rhys

Additional information: Net-SNMP comes with a handy little script that - if it's in the user's PATH - helps find the site-wide MIBs. E.g.:

$SITE_PREFIX = `net-snmp-config --prefix`;
chomp $SITE_PREFIX;
$DEF_MIB_DIR = "$SITE_PREFIX/share/snmp/mibs";
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I should be able to create a subdirectory under that named after my package, then subdirs as usual. Then use the addMibDir() trick above combined with the readdir() method suggested by idsfa, and I think we're there!

I'll still want to add some exception handling code for the cases where net-snmp-config can't be found or the MIB files were moved (e.g. can't stat "$SITE_PREFIX/share/snmp/mibs"), and some other stuff. Might put some user-prompting in there for help, but this is getting close.

--Rhys

You could extend the SNMP class to add your needed code to the mib loading method and then SUPER:: it. This would probably be more work than adding the few lines you need.

Also, you probably ought to avoid that `ls` construction and go with readdir ...

$root="/usr/local/share/snmp/mibs/TEMP";
opendir(DIR, $root) || die "can't opendir $root: $!";
map { &SNMP::addMibDirs($_); } 
          grep { ! /^\./ && -d "$root/$_" } readdir(DIR);
closedir DIR;
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Which also avoids accidentally trying to add files as MibDirs and is safer and more portable.

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Remember, when you stare long into the abyss, you could have been home eating ice cream.