I have a very large file, 9 million records, and there are sections in the file where I need to join records. How can I get for example line number 100,000 and join to it lines 100,001-100,050 using sed or awk? The joins need to happen multiple times throughout the file. I can get the line number for the first and last line I need in my join but am having difficulty figuring out how to reformat the file with the lines joined and the file saved with the one end-resulting line.

Any...