[GTALUG] GRUB's DSL and looping

[Giles Orr]

On 25 July 2018 at 13:45, Lennart Sorensen via talk <talk at gtalug.org> wrote:

> 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
> ...
>

Thank you!

I don't think that's documented anywhere, and it doesn't strike me as being
in any way obvious.

-- 
Giles
https://www.gilesorr.com/
gilesorr at gmail.com
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