How do I add a line after another line in a file, in Ruby?

Question

Updated description to be clearer.

Say I have a file and it has these lines in it.

one
two
three
five

How do I add a line that says "four" after the line that says "three" so my file now looks like this?

one 
two
three
four
five

Answer 1

Assuming you want to do this with the FileEdit class.

Chef::Util::FileEdit.new('/path/to/file').insert_line_after_match(/three/, 'four')