[GTALUG] GRUB's DSL and looping

[Lennart Sorensen]

On Wed, Jul 25, 2018 at 12:54:39PM -0400, Giles Orr via talk wrote:
> There's probably a GRUB-specific mailing list or forum, but I thought I
> would try here first ...
> 
> GRUB has a DSL ( https://en.wikipedia.org/wiki/Domain-specific_language )
> that looks a lot like shell scripting.  Most people never see it as it's
> used to generate the menus we use at boot-time and they see only the menus,
> but it can do some interesting things - particularly when you're dealing
> with multi-boot USB sticks.  Here's a simple but slightly useful example:
> 
> function cpuinfo {
>     # only able to determine: 32/64 bit, and is it PAE
>     echo "GRUB's ability to analyse processors is limited, we can only tell
> you:"
>     if cpuid -p; then
>         pae_assessment="PAE"
>     else
>         pae_assessment="NO PAE"
>     fi
>     if cpuid -l; then
>         echo "64-bit processor, $pae_assessment"
>     else
>         echo "32-bit processor, $pae_assessment"
>     fi
> }
> 
> But it has some nasty limitations that are frustrating me:
> - no pipes
> - no command substitution
> - no file globbing

Actually it does file globbing if you load the regexp module.

Apparently this works:

insmod regexp
for i in /boot/*; do echo $i; done

Or:

grub> ls /boot/*
error: file `/boot/*' not found.
grub> insmod regexp
grub> ls /boot/*
unicode.pf2 i386-pc/ locale/ fonts/ grubenv grub.cfg
config-4.16.0-2-amd64
...

-- 
Len Sorensen