It may be hard to find by Googling by it's really quite simple and quicker than reading dozens of man page entries.
sed -n 5p somefile.txt
Just replace the 5 with whatever line you want to be printed.........
This is a "pro" feature I guess so you don't have to see the ugly GRUB screen but if you're having boot problems or trying to update/customize your system it can be frustrating.You have to do some Googling to find out that you have to hold shift to see the GRUB2 menu.
You have to hold shift before GRUB2 loads and you will see it........