21 Jan
2020
21 Jan
'20
5:51 a.m.
I also make new shells fairly regularly, about half the time because I wan
to set some variables that I don't want to have to reset. Then if/when I
forget which window I was in, I can check with SHLVL (at least when using
bash, which I normally don't do). But I'm normally in & out of the
sub-shells very quickly so don't often need to check.
Terry
On Mon, Jan 20, 2020 at 8:43 PM Theodore Y. Ts'o <tytso(a)mit.edu> wrote:
On Mon, Jan 20, 2020 at 09:15:56AM +0100, markus
schnalke wrote:
Hoi.
[2020-01-19 14:22] Grant Taylor via TUHS <tuhs(a)minnie.tuhs.org>
>
> Have you ever used shell level, $SHLVL, in your weekly ~> daily use of
Unix?
What's the use of it? The only use of $SHLVL I can think of is the
answer to the question if ^D will close the last shell or just a
sub shell. I hardly ever ask myself this question. Probably that
starts to become relevant when you open sub shells frequently.
<Raises hand>
The normal reason why I'm starting subshells is because I need to
control various environment variables on an ad-hoc basis. It might be
PYTHONPATH, KRB5CCNAME, GPG_AGENT_INFO, LD_LIBRARY_PATH, or some
combination of the above. Back when I was regularly using Kerberos
root/admin bits, I had some hard-coded shell aliases to indicate
explicitly I was in a shell that was using my
tytso/root(a)ATHENA.MIT.EDU or tytso/admin(a)ATHENA.MIT.EDU kerberos
tickets.
But for ad-hoc use cases, SHLVL is great way to track whether I'm a
non-standard shell environment. For me, some use case probably comes
up at least week or two.
With tmux or screen at hand, this use case is
obsolete for me.
(Besides, my shell doesn't know about $SHLVL.)
Before I was using bash regularly, I had hard-coded something like
SHLVL in my .tcshrc.
- Ted