busybox/testsuite/hostid/hostid-works

h=x$(busybox hostid)
# Is $h a sequence of hex numbers?
x="${h//[0123456789abcdef]/x}"
x="${x//xxx/x}"
x="${x//xxx/x}"
x="${x//xxx/x}"
x="${x//xx/x}"
test x"$x" = x"x"