>From XRAT
A.8.3, the value is advisory, and need not be a directly resolvable path by
means the standard provides. What constitutes a valid value for a platform
should be documented, and I'd see making that a requirement, as to what applies
to the utilities it provides that make use of the
In Issue 7, 2016 Edition, Section 8.3 "Other Environment Variables",
page 178, line 5864:
SHELL This variable shall represent a pathname of the user's
preferred command language interpreter. [...]
This is ambiguous, as it does not exclude a relative pathname, and
doesn't say
