Hold Space

22

Heading translation in `sed`

The interesting part is:

        /^\(.\)\1\1*$/ { x; 
                         y/abcdefghijklmnopqrstuvwxyz/ABCDEFGHIJKLMNOPQRSTUVWXYZ/;
                                      x; d;
                       }

/^\(.\)\1\1*$/ is a pattern

it matches lines that have 2 or more occurrences of the same character

and nothing else

For these lines, we first retrieve the hold space (x)

(that's the previous line of input)

Translate to upper case (y/.../.../)

Put it back in the hold space as if it had been uppercase all along

And skip to the next line of input, printing nothing d