I suppose that my last two posts need some clarification and I believe that it's because of me English

By obvious I meant that it was obvious, that you meant something different, not that the issue was obvious.

When I first read your post, I thought that your confusion was deriving from something different (too complicated for me to explain in English and not important at this time).

radoulov in your code below kindly what is the "x" for?

awk '$0~"^"(NR==1?"\"":x "http:")&&$0=RS$0RS' RS=\"

x is for NULL(or empty) string It's an uninitialized variable.
You can use "" if you find it more readable. x is just shorter.

If you want to become proficient in unix, regex. as it is called is a very important tool. It has spilled over into Windows programming in the past few years as well.