Env var feature request

[Erik Keever]

Hello,

A recent conversation with a member of our research team leads me to propose 
the following feature request:

A --debug-envvars flag which will, when passed to bash, catch every time an 
environment variable is set and print the file/line that is setting it. To 
restrict it, "--debug-envvars FOO,BAR" to catch only instances of FOO or BAR 
being set.

Some vendor development environments substantially amend your environment when 
loaded (e.g. OneAPI) and others will, by default, flat out overwrite basic 
things like what compiler you're using (Hi there, Cray HPC toolkit!) and this 
sometimes leads to Issues. Even if not chasing down problems relating to such 
esoterica as these, the problem originated from one of our guys trying to chase 
down a mystery PATH entry being set by an AWS instance. In his words, "Yes! 
That'd be awesome! Would have saved me a lot of time the last year."

I assume this is not already available, or Google would not have a thousand 
results from StackOverflow which are all some variation on the theme of "grep 
/etc for the variable name."

-- Erik