Re: (shellcheck) SC2103

On 05.03.2025 19:40, Kaz Kylheku wrote:

On 2025-03-05, Kenny McCormack <gazelle@shell.xmission.com> wrote:

All testing done with shellcheck version 0.10.0 and bash under Linux.
>
Shellcheck says that you should replace code like:
>
    cd somedir
    do_something
    cd .. # (Or, cd -, which is almost, but not exactly the same thing)
>
with
>
    (
    cd somedir
    do_something
    )

 
That obviously won't work if do_something has to set a variable
that is then visible to the rest of the script.

Indeed. Only for strict hierarchical semantics it makes sense.

 
Forking a process just to preserve a current working directory
is wasteful; we wouldn't do that in a C program, where we might
open the current directory to be saved, and then fchdir back to it.

Shells may be different. While Bash regularly creates a subprocess,
Ksh in certain structures creates just a "subshell context" without
forking/cloning an own process.

[...]
 

but the more general pattern would be:
>
    cd somewhere;...;cd -

 
cd - will break if any of the steps in between happen to to cd;
it is hostile toward maintenance of the script.

Indeed.

Just note that spending a "subshell context"[Ksh] or a subprocess
[Bash] keeps the structure intact. (If you want to pay for that;
especially when it's costly [as in Bash].)

Janis

[...]