I can see what happened now.  The one line script which failed is this, 
"test.rb"

require "iconv"

In the same directory was the script from my previous post, named 
"iconv.rb".  Evidently there is some rule of precedence here whereby 
when running test.rb, ruby first looked in the relative path and loaded 
iconv.rb causing the error.  This is consistent.

What is confusing and inconsistent is that running "iconv.rb" as itself 
works sometimes but not others.  Renaming it obviously prevents the 
problem.

Sorry again.
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