I want to execute from a grub a very small linux that only has commands, so at startup it executes this shell script I wrote and after that the user has an option to go back to the grub.

I've heard of busybox but that doesn't seem to be helpful?

Can anyone recommend a non gui distro, that can help me achieve this.

Thanks,

I don't know of a real distribution for this. That's kind of overkill by definition. You don't need a package repository, you don't need much of anything at all, just a kernel and a bundle of files.

See initramfs on how to make that bundle of files. You'd probably use busybox in it -- it's a single swiss-army-knife executable which you can use like busybox cp source destination if you want cp, busybox cat filename if you want cat, etc, etc. Be sure to have a symlink /bin/sh pointing to /bin/busybox so scripts can run.

Just put whatever script you want into init instead of the stuff you'd use to chroot into a real system.

Going back to grub isn't trivial. You can't just "quit linux" and go back to grub. The kexec option allows you to boot another kernel, which would allow you to boot grub raw again without rebooting, but would take some fiddling to manage. The quick and dirty way to manage it is, of course, to just reboot...