So replacing all tabs in a file with spaces is not hard.
In vim for example, I can do
And if I want to replace the ones at the beginning of each line, not the one in the middle I can do
But if there are line with one and lines with more tabs at the beginning, and lines with tabs in the middle, and I want to replace each tab in the beginning of a line with spaces to keep the indentation structure of the file, that is what I don't know how to do.
In vim or sed or generally using regular expressions.