MFC:

r346018 | imp | 2019-04-07 12:39:55 -0600 (Sun, 07 Apr 2019) | 6 lines

Use default shell assignment rather more complicated if then
construct.

Discussed with: emaste@, allanjude@ (changes (or not) based on their feedback)
Differential Revision: https://reviews.freebsd.org/D19797