modernize `tbg`

[psychocoderHPC]

• rename some variables, no need to start variables with tooltpl anymore since we removed a lot of our ugly sed magic in #4905
• use $(command) indtead of 'comamnd'

[psychocoderHPC]

This will give a small overview about both ways to execute an command https://www.redhat.com/sysadmin/backtick-operator-vs-parens

[PrometheusPi]

If I run my test from this morning, I get a grep warning:

grep: character class syntax is [[:space:]], not [:space:]

and it takes longer, now 28s.

[chillenzer]

I'm not familiar enough with the code of this to see if there are any bad things hidden under a thick layer of trivial changes. Two suggestions:

1. Splitting this into several commits might help reviewing this.
2. Most of the changes I've seen are not something anyone should be doing by hand. Should we adapt shellcheck. Not sure if this one also automatically applies fixes but probably something like that exists.

[psychocoderHPC]

1. Splitting this into several commits might help reviewing this.

All changes are in one file splitting it now will only introduce errors.

2. Most of the changes I've seen are not something anyone should be doing by hand. Should we adapt shellcheck. Not sure if this one also automatically applies fixes but probably something like that exists.

Yes, we can do it independent of this PR.