The file was analyzed with shellcheck, and various issues fixed. Most of
the problems were just cleanups, but also potential bugs were fixed.

Many variables were quoted with double quotes to prevent globbing. The
local_files array expansion was quoted so that any file names with
potential spaces in the filename would not be re-split. The empty
default value was removed from the list processing. POSIX standard "grep
-E" was used instead of egrep.