Linux remove space/column if matching string pattern - awk

Question

I would like awk or sed or any other display filter mechanisms in native shell to be able to remove space from string lines that a match & do not remove any space between the 2 strings (columns) when not matched. And then display the output.
My file:
# cat test2
col0 col1 col2 col3 col4 col5
ln1 abc def ghi jkl mno
ln2 abc defghi jkl mno pqr
My output I would like to be:
# <something to view/grep/filter with> test2
col0 col1 col2 col3 col4 col5
ln1 abc defghi jkl mno
ln2 abc defghi jkl mno pqr
I have tried multiple combinations of grep & awk & cut. But not able to do it. I am not good with sed, but I can try. I even tried to use an interim file i.e. echo output to some file & then grep. But I failed to do that too.
Edited with more of my requirement:
My biggest problem is that I can't predict where the space will be & what the contents of the row entries would be. So I would like sed to get the output not based on a specific string but instead based on column numbers.
My file:
# cat test2
col0 col1 col2 col3 col4 col5
ln1 abc def ghi jkl mno
ln2 abc defghi jkl mno pqr
ln3 aaa bbb ccc ddd eee
ln4 aaa bbbccc ddd eee
Output File:
# <something to view/grep/filter with> test2
col0 col1 col2 col3 col4 col5
ln1 abc def ghi jkl mno
ln2 abc defghi jkl mno pqr
ln3 aaa bbbccc ddd eee
ln4 aaa bbbccc ddd eee

Answer 1

sed 's/def ghi/defghi/' file
If that's not what you wanted then edit your question to clarify your requirements and provide input/output that better demonstrates your problem.