very extensive "Portable Shell Programming" chapter: https://www.gnu.org/savannah-checkouts/gnu/autoconf/manual/autoconf-2.71/html_node/Portable-Shell.html
I know. The Autoconf manual already describes this issue in detail. The point of the brief mention in the Automake manual is because it is precisely the place and the problem that are rather likely to come up in practice. I see I failed to link to the Autoconf node, though. I'll add that. -k