thank you, maybe I should not use the word "block", I should say pattern.

like the text file I have given in the first post, the first line starts with a symbol "@", and the third line starts with "+",the other part are identical, but not identical in other four-lines.

the even lines are of the same length in the whole text file.

the whole file follow this pattern.

I am a newbie. sorry for my careless.