Make the script more portable:

grub.mkconfig is built from gub-mkconfig.in with something like this:

grub-mkconfig: util/grub-mkconfig.in  $(top_builddir)/config.status
	$(top_builddir)/config.status --file=-:$< | sed -e 's,@pkglib_DATA@,$(pkglib_DATA),g' > $@
	chmod a+x grub-mkconfig

autotools do the substitutions of placeholders used in grub-mkconfig.in

prefix=@prefix@
exec_prefix=@exec_prefix@
sbindir=@sbindir@
bindir=@bindir@
libdir=@libdir@
sysconfdir=@sysconfdir@
PACKAGE_NAME=@PACKAGE_NAME@
PACKAGE_VERSION=@PACKAGE_VERSION@
host_os=@host_os@
datarootdir=@datarootdir@
datadir=@datadir@
pkgdatadir=${datadir}/`echo @PACKAGE_TARNAME@ | sed "${transform}"`
