Shell Programming and Scripting

Hi,

I'm new to sed and i'm having a few difficulties.. I need to append the current line to the pattern space, which already contains that same line, e.g.:
current line : test
pattern space : test|test

I was able to do this using the hold space, but the problem is that in the next step of the exercise, the hold space is being used for another purpose, so I shouldn't clear it.

I thought maybe I could tell sed to move the current line back up and use the N-command. But how do you decrease the index of the current line? Or is there another way to do this?

Thanks in advance!

Hello, delucasvb:

Once sed has read a line, it cannot back up to read it again. If you need to use a line more than once, you need to store it in the pattern space, hold space, or write it to a tmp file and then read it when needed.

If all you need to do is duplicate the contents of the pattern space, you can do:

Code:

s/.*/&&/

Regards,
Alister

Ah, I overlooked the usage of special characters for the s-command. This is certainly useful for many more purposes. Thanks Alister!