Re: unexpected behavior

[Davide Brini]

On Thu, 12 Jan 2023 18:24:11 +0100, Christof Warlich <cwarlich@gmx.de>
wrote:

> Hi,
> 
> can anyone explain why the following line prints 0 instead of 1?:
> 
> $ stat=0; false || echo hi && echo ho && stat=1 | tee /dev/null; echo
> $stat hi
> ho
> 0
> 
> It does what I'd expect when removing the pipe, so it's obviously caused
> by some pipe magic going on ...:
> 
> $ stat=0; false || echo hi && echo ho && stat=1; echo $stat
> hi
> ho
> 1

Yes, introducing the pipe makes the "stat=1" part run in a subshell, so the
change is not seen in the parent shell. Here's another simple example:

x=0; x=1 | cat; echo $x   # 0

x=0; echo 10 | read x; echo $x   # 0

(the previous one would work in some shells; just not in bash with
the default settings)

One possible workaround is to use the value you need while still in the
subshell, for example:

x=0; echo 10 | { read x; echo $x; }    # 10

See also https://mywiki.wooledge.org/BashFAQ/024 for more details.


-- 
D.