[GTALUG] GRUB's DSL and looping

[Giles Orr]

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

That last in particular is really getting on my nerves.  I want to source
all the files in one folder, but I can't say 'for file in folder/* ; do'
because the '*' is a literal character, no special meaning.  Likewise, I
can't say 'for file in `ls folder/` ; do' because there's no command
substitution.

I was wondering if anyone knows of a solution to this problem.  Or even if
you have ideas from long-gone old shells with similar limitations for which
someone worked out a nasty work-around ...  What I've been doing is 'for
file in name1 name2 name3 ... ; do', but of course this only works if you
remember to add new filenames to the list.

I've googled quite a bit, but most people only modify GRUB through
/etc/default/grub or, if they're really adventurous, through
/etc/grub.d/40_custom or similar.  What I'm looking for is (mostly) at a
lower level than that, and examples are surprisingly hard to come by.  And
search results are occasionally polluted by GRUB4DOS results ... GRUB4DOS
_does_ seem to support file globbing.  All very confusing.  Thanks.

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