Alternative to ${cmdpath} which returns just the device

[SevenBits]

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Hello there,

I'm the developer of Mac Linux USB Loader and Enterprise, two
Mac-related UEFI tools. Enterprise, one of the components, uses GRUB
to boot Linux kernels. Since I've compiled GRUB as x86-64 and it's
creating the image with the grub-mkstandalone command, the initial
root from GRUB is the memdisk, accessible via the (memdisk) device.

Several months ago, I was pointed to the ${cmdpath} variable, which
has proven very useful. However, on my setup, when booting from UEFI,
that variable contains the device *and* the path to the folder
containing the GRUB executable, for example:

(hd0,gp1)/efi/boot/

In 90% of cases, this is great, however, I need a way to get just the
device GRUB was booted from, and not the path to the executable. Is
this possible?

- -- SevenBits
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