> Where I actually struggled with what's expected is Day 11. Just the lines from the files are wanted, not the files names. It took me a little while to cotton

> Where I actually struggled with what's expected is Day 11. Just the lines from the files are wanted, not the files names. It took me a little while to cotton on to that. Semi-spoiler follows. So you need to use the appropriate flag with grep to suppress the file names.