Ruby: Insert a character into a string?

Question

1
00:00:00000  -->00:00:00000
2
00:00:00730  -->00:00:04280
So when Sam originally sent me an email to do this course,  
3
00:00:04280  -->00:00:08400
he said Ben can you teach a 50 minute course on management.

I want to insert a , into :00730 , so it becomes :00,730 . How can I do that?

I'm thinking about

  path = 'lib/subtitle.txt'
  lines = IO.readlines(path).map do |line|
    *if contains 5 number, then insert a comma into it, like `gsub?`
  end
  File.open(path, 'w') do |file|
    file.puts lines
  end

But I'm not very familiar with Regex, is there a simpler way of doing this?

Answer 1

Using regular expression - capturing group and backreference ( String#gsub ):

"00:00:04280  -->00:00:08400".gsub(/(\d{2})(\d{3})/, '\1,\2')
# => "00:00:04,280  -->00:00:08,400"

capturing groups (...) can be referenced in replacement string with \\1 , \\2 (reference first, second captured group)

Answer 2

You also can simply run

`sed -i.bak 's/^\([[:digit:]]\{2\}:[[:digit:]]\{2\}:[[:digit:]]\{2\}\)\([[:digit:]]\{3\}  -->[[:digit:]]\{2\}:[[:digit:]]\{2\}:[[:digit:]]\{2\}\)\([[:digit:]]\{3\}\)$/\1,\2,\3/' lib/subtitle.txt `

This creates backup file and makes changes you need.