GRUB2 will usually prompt you to

• boot off the current option
• edit the current option
• move to another option
• access to the command line

On the (GRUB) command line you can type any of the GRUB commands. You get TAB-completion.

Be warned, you don't get the functions defined in grub.cfg (eg. load_video). You'll need to memorise what the individual grub commands are (usually a series of insmod commands) and type them in by hand.

One particularly useful interactive command is ls.

A simple ls will give you a list of disks and partitions: hd0, (hd0,msdos1), (hd2,gpt1) etc..

Combine the disk or partition with a pathname to get the contents of the disk/parititon, eg. ls (hd2,gpt1)/.

Confusingly, hd0 is usually the current Boot device so it depends on which GRUB menu you decide to access the command line from...