Hi ephemeric,

A little late but here's a try with Perl. This is like hippo's solution but it adds the detection of whether the parameter has already been added or not. Personally I don't mind breaking up regexes into several regexes if it helps in thinking about the solution.

perl -pe 's/"\s*$/ transparent_hugepage=never"/ if /^GRUB_CMDLINE_LINU
+X=/ && !/transparent_hugepage/' filename
[download]

Hope this helps,
-- Hauke D