Re: Default PATH setting - reduce to something more sensible?

In article <vmu94j$1q2lp$1@dont-email.me>,
Janis Papanagnou  <janis_papanagnou+ng@hotmail.com> wrote:

On 23.01.2025 17:47, Dan Cross wrote:

[snip]
 
: term; echo $HOME
/home/cross
: term; pwd
/home/cross
: term; echo echo xyzzy >bin/quux
: term; chmod +x bin/quux
: term; which quux
/home/cross/bin/quux
: term; quux
xyzzy
: term; exec ksh
: term; export PATH=~/bin:/bin:/usr/bin
: term; echo $PATH
/home/cross/bin:/bin:/usr/bin
: term; which quux
/home/cross/bin/quux
: term; quux
xyzzy
: term; export PATH="$HOME/bin:/bin:/usr/bin"
: term; echo $PATH
/home/cross/bin:/bin:/usr/bin
: term; which quux
/home/cross/bin/quux
: term; quux
xyzzy
: term; export PATH="~/bin:/bin:/usr/bin"
: term; echo $PATH
~/bin:/bin:/usr/bin
: term; which quux
: term; quux
ksh: quux: not found
: term; exec /usr/pkg/bin/bash
: term; echo $PATH
~/bin:/bin:/usr/bin
: term; which quux
: term; quux
xyzzy
: term;

>
Bash behaves strange here; 'which' doesn't find the executable but
nonetheless bash executes it, shows its output?

Bash doesn't behave strangely here at all.  Outside of its POSIX
mode, it's free to implement whatever behavior it likes with
respect to `~` expansion, and this is the behavior the author
has chosen.

But, critically, that does not mean that the programs _that it
invokes_ have to do the same.  So while `bash` can perform `~`
expansion on the components of $PATH when it's searching for a
program to execute, one shouldn't be surprised if other programs
don't do the same thing.

As was pointed out, `which` is not built into the shell, and
therefore, not obligated to follow `bash`'s expansion rules.

I've changed the above test frame to remove some unnecessary parts
to eliminate distracting complexity. The output for three shells:

Sorry, I think this cuts too much: the point was to show how the
different shells handle `~` in different contexts; the actual
strings that are in `$PATH` are important to show.

[snip]

I suppose the moral is, for maximal portability, prefer using
$HOME (or another similar variable) to `~` when setting $PATH
unless you're doing so in a context where you are sure that `~`
will be expanded during assignment.

>
IMO, the consequence is to not quote a tilde expression in the first
place if you want it expanded in a shell variable. *Violating* that
rule will _in Bash_ produce this strange effect (in the given setup).
>
To me it appears that not finding (by 'which') an executable but
executing it nonetheless qualifies as a bug [in Bash].

Not a bug, but yes, surprising.

- Dan C.