Insert space before some character if space does not exist

Question

If a have a string like:

"_test_teste2 _test3"

how can I add a space before the _ that don't have a space before already and are not in the start of the string?

Ex:

"_test _teste2 _test3"

I tried this:

todo.desc = todo.desc.gsub /_/, " _"

It works, but add spaces after every _.

Thanks in advance.

Answer 1

>> "_abc_de _e _f_tes_fefe".gsub(/(\S)_/,'\1 _')
=> "_abc _de _e _f _tes _fefe"