Re: interactive shell detection in shrc

[RVP <rvp%SDF.ORG@localhost>]

On Mon, 30 Sep 2024, Greg A. Woods wrote:

> > SHELL is set by ksh and not by sh (sh handles NETBSD_SHELL), if I'm
> > not mistaken?
>
> login(1) sets $SHELL, [...]

and also by programs which start a shell in a pty: xterm/script/tmux/...
However, xterm _doesn't_ set SHELL if what was passed is not in /etc/shells:

```
$ uname -a
Linux CoreBook 6.8.0-45-generic #45-Ubuntu SMP PREEMPT_DYNAMIC Fri Aug 30 12:02:04 UTC 2024 x86_64 x86_64 x86_64 GNU/Linux
$ cat /etc/shells 
# /etc/shells: valid login shells
/bin/sh
/usr/bin/sh
/bin/bash
/usr/bin/bash
/bin/rbash
/usr/bin/rbash
/usr/bin/dash
$ env SHELL=/bin/dash xterm -e 'printf ">%s<\n" "$SHELL"; read x'
```

On Mon, 30 Sep 2024, tlaronde%kergis.com@localhost wrote:

> What I mean is that if I'm under ksh, and then I switch to sh even
> explicitely setting interactive :
>
> $ printenv
>
> _=/usr/bin/printenv
> ...
> SHELL=/bin/ksh
> ...
>
> $ sh -i
> $ printenv
>
> ...
> SHELL=/bin/ksh
> ...
>
> and the same result with "sh -l" (supposed to be considered a login
> shell).
>
> So how can the test be reliable in all circumstances?

Set SHELL explicitly?

```
$ echo $SHELL
/bin/bash
$ env SHELL=/bin/dash dash
$ echo $SHELL
/bin/dash
$
```

-RVP