Replace file entries in subdirectories with sed from list - sed

Question

I want to replace a certain line (#6) in a whole bunch of documents that looks like this:
N Metal1 Metal2 Metal3 Metal4
where the metals need to be replaced with chemical symbols from a list of permutations:
CrHfMoNb CrHfMoTa CrHfMoTi CrHfMoV CrHfMoW CrHfMoZr CrHfNbTa CrHfNbTi CrHfNbV CrHfNbW CrHfNbZr CrHfTaTi CrHfTaV CrHfTaW CrHfTaZr CrHfTiV CrHfTiW CrHfTiZr CrHfVW CrHfVZr CrHfWZr CrMoNbTa CrMoNbTi CrMoNbV CrMoNbW CrMoNbZr CrMoTaTi CrMoTaV CrMoTaW CrMoTaZr CrMoTiV CrMoTiW CrMoTiZr CrMoVW CrMoVZr CrMoWZr CrNbTaTi CrNbTaV CrNbTaW CrNbTaZr CrNbTiV CrNbTiW CrNbTiZr CrNbVW CrNbVZr CrNbWZr CrTaTiV CrTaTiW CrTaTiZr CrTaVW CrTaVZr CrTaWZr CrTiVW CrTiVZr CrTiWZr CrVWZr HfMoNbTa HfMoNbTi HfMoNbV HfMoNbW HfMoNbZr HfMoTaTi HfMoTaV HfMoTaW HfMoTaZr HfMoTiV HfMoTiW HfMoTiZr HfMoVW HfMoVZr HfMoWZr HfNbTaTi HfNbTaV HfNbTaW HfNbTaZr HfNbTiV HfNbTiW HfNbTiZr HfNbVW HfNbVZr HfNbWZr HfTaTiV HfTaTiW HfTaTiZr HfTaVW HfTaVZr HfTaWZr HfTiVW HfTiVZr HfTiWZr HfVWZr MoNbTaTi MoNbTaV MoNbTaW MoNbTaZr MoNbTiV MoNbTiW MoNbTiZr MoNbVW MoNbVZr MoNbWZr MoTaTiV MoTaTiW MoTaTiZr MoTaVW MoTaVZr MoTaWZr MoTiVW MoTiVZr MoTiWZr MoVWZr NbTaTiV NbTaTiW NbTaTiZr NbTaVW NbTaVZr NbTaWZr NbTiVW NbTiVZr NbTiWZr NbVWZr TaTiVW TaTiVZr TaTiWZr TaVWZr TiVWZr
to make it look for example like this:
N Cr Hf Mo Nb
I can do this easily with the sed command using:
sed -i '6s/Metal1 Metal2 Metal3 Metal4/Cr Hf Mo Nb/' filename`
The problem is that I need to do it automatically for all 126 combinations, where each file is residing in its own subdirectory for each composition and has to be adjusted accordingly to its own elements. The file always has the same name and is completely identical before this change.
The chemical symbols have to be listed alphabetically and there must be one space between each, or the code won't work. I assume this is difficult because all the used elements have two letters in their symbols except for V. Is there an efficient way to do this?

Answer 1

Handling the two-char (Zr) one-char (W) problem is easy. Each capital letter marks the beginning of a new element.
cd dir/
for dir in *N; do
split="$(sed 's/N$//;s/[A-Z]/ &/g' <<< "$dir")"
sed -i "s/N Metal1 Metal2 Metal3 Metal4/N $split/" "$dir/file"
done
Note that $split starts with a space, so the replacement string is something like N Cr Hf Mo Nb with two spaces between N and Cr – just as you wanted.