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From: Janis Papanagnou <janis_papanagnou+ng@hotmail.com>
Newsgroups: comp.unix.shell
Subject: Re: (shellcheck) SC2103
Date: Wed, 5 Mar 2025 20:02:05 +0100
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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

> [...]