wordexp IFS fixes

[Tim Waugh]

On 7 Sep 1998, Andreas Schwab wrote:

> Note that IFS splitting only occurs when any expansion is done at all.
> This closes a well known sh security bug.

Ah.  The current wordexp implementation performs IFS splitting even when
no expansion has happened.

Re-reading 3.6.5, it looks like "the shell shall scan the results of
expansions and substitutions that did not occur in double-quotes for field
splitting" means that field splitting cannot occur just on its own (set
:abc:).

Is this the case then?  If so, I think that some of the wordexp test cases
are wrong (the first few for instance)..

Bash says that "set a b c" sets three positional parameters, so is this
security hole only for non-whitespace IFS?

Tim.
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