First, unrelated to your main task: you don't need to say eval {...} or die $!, for several reasons. The first is that if it throws an exception, you can probably use the original exception :) Second, the or there is dangerous unless makeCommandsSub is guaranteed to return a true value; the valuation of an eval is (like any other block of Perl 5) its last evaluated thing. So

eval { 0 } or die "this dies, but not because of an exception in the i
+nner block!";
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Finally, $! is wrong in this case, you need $@ for the exception.

But to your real question:

You said 'BigDB\::$cmd'. But because of the single quotes, this creates literally a '$cmd' package in BigDB's symbol table! (Check by printing keys %BigDB::.) The correct code is

*{"BigDB::$cmd"} = ...
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You probably got the backslash from code that used a variable containing the caller, where it's needed to make Perl not think you're talking about a fully qualified variable:

*{"$caller\::methodname"} = ...
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