inconsistency between bash and zsh subshells

inconsistency between bash and zsh subshells

[Matt Zagrabelny]

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Greetings zsh-users,

I'm using zsh 5.8.1 (Debian).

I am seeing inconsistent behavior between using a subshell in the branch of
a conditional in bash and zsh.

zsh:

zsh$ rm -f /tmp/FOO
zsh$ ls /tmp/FOO 2> /dev/null || echo "no /tmp/FOO"
no /tmp/FOO
zsh$ echo | while read LINE; do IP=$(echo $LINE | cut -d ' ' -f 1); if [ -n
"$IP" ]; then echo FOO; FOO=$(touch /tmp/FOO); else echo BAR; fi; done; ls
/tmp/FOO 2> /dev/null || echo "no /tmp/FOO"
BAR
/tmp/FOO

Why does the subshell in zsh get executed even though the conditional
branch is not? That is, the "touch"-ing of /tmp/FOO.


bash:

bash$ rm -f /tmp/FOO
bash$ ls /tmp/FOO 2> /dev/null || echo "no /tmp/FOO"
no /tmp/FOO
bash$ echo | while read LINE; do IP=$(echo $LINE | cut -d ' ' -f 1); if [
-n "$IP" ]; then echo FOO; FOO=$(touch /tmp/FOO); else echo BAR; fi; done;
ls /tmp/FOO 2> /dev/null || echo "no /tmp/FOO"
BAR
no /tmp/FOO

The bash output is what I would expect zsh to execute/output as well.

Thanks for helping me understand this.

Cheers!

-m

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Re: inconsistency between bash and zsh subshells

[Mikael Magnusson]

On 5/23/22, Matt Zagrabelny <mzagrabe@d.umn.edu> wrote:
> Greetings zsh-users,
>
> I'm using zsh 5.8.1 (Debian).
>
> I am seeing inconsistent behavior between using a subshell in the branch of
> a conditional in bash and zsh.
>
> zsh:
>
> zsh$ rm -f /tmp/FOO
> zsh$ ls /tmp/FOO 2> /dev/null || echo "no /tmp/FOO"
> no /tmp/FOO
> zsh$ echo | while read LINE; do IP=$(echo $LINE | cut -d ' ' -f 1); if [ -n
> "$IP" ]; then echo FOO; FOO=$(touch /tmp/FOO); else echo BAR; fi; done; ls
> /tmp/FOO 2> /dev/null || echo "no /tmp/FOO"
> BAR
> /tmp/FOO
>
> Why does the subshell in zsh get executed even though the conditional
> branch is not? That is, the "touch"-ing of /tmp/FOO.

You're most likely using a poorly written prompt theme and/or thing
that updates your terminal title. Try disabling that code and try
again if so.

-- 
Mikael Magnusson

Re: inconsistency between bash and zsh subshells

[Matt Zagrabelny]

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On Mon, May 23, 2022 at 12:01 PM Mikael Magnusson <mikachu@gmail.com> wrote:

> On 5/23/22, Matt Zagrabelny <mzagrabe@d.umn.edu> wrote:
>
> > Why does the subshell in zsh get executed even though the conditional
> > branch is not? That is, the "touch"-ing of /tmp/FOO.
>
> You're most likely using a poorly written prompt theme and/or thing
> that updates your terminal title.


Haha. Probably!



> Try disabling that code and try
> again if so.
>

Yup - that was it. I removed my .zshrc and it works as expected.

Thanks for the hint! Time to figure out what poorly written part of my
.zshrc is to blame.

Cheers,

-m

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Re: inconsistency between bash and zsh subshells

[Mikael Magnusson]

On 5/23/22, Matt Zagrabelny <mzagrabe@d.umn.edu> wrote:
> On Mon, May 23, 2022 at 12:01 PM Mikael Magnusson <mikachu@gmail.com>
> wrote:
>
>> On 5/23/22, Matt Zagrabelny <mzagrabe@d.umn.edu> wrote:
>>
>> > Why does the subshell in zsh get executed even though the conditional
>> > branch is not? That is, the "touch"-ing of /tmp/FOO.
>>
>> You're most likely using a poorly written prompt theme and/or thing
>> that updates your terminal title.
>
>
> Haha. Probably!
>
>
>
>> Try disabling that code and try
>> again if so.
>>
>
> Yup - that was it. I removed my .zshrc and it works as expected.
>
> Thanks for the hint! Time to figure out what poorly written part of my
> .zshrc is to blame.

It will probably be something involving print -P and \a or \007 in
something named preexec. If you change $1 in that to \$1 it is more
likely to work, though it's of course hard to say without seeing the
particular code. If you instead remove any setopt printsubst it should
work fine without modifying the preexec function. (only do one of
these changes). Basically what's happening is you're expanding the
string to put in the title twice, resulting in things like $()
actually being executed which is usually not great.

-- 
Mikael Magnusson

Re: inconsistency between bash and zsh subshells

[Matt Zagrabelny]

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On Mon, May 23, 2022 at 12:32 PM Mikael Magnusson <mikachu@gmail.com> wrote:

> On 5/23/22, Matt Zagrabelny <mzagrabe@d.umn.edu> wrote:
> > On Mon, May 23, 2022 at 12:01 PM Mikael Magnusson <mikachu@gmail.com>
> > wrote:
> >
> >> On 5/23/22, Matt Zagrabelny <mzagrabe@d.umn.edu> wrote:
> >>
> >> > Why does the subshell in zsh get executed even though the conditional
> >> > branch is not? That is, the "touch"-ing of /tmp/FOO.
> >>
> >> You're most likely using a poorly written prompt theme and/or thing
> >> that updates your terminal title.
> >
> >
> > Haha. Probably!
> >
> >
> >
> >> Try disabling that code and try
> >> again if so.
> >>
> >
> > Yup - that was it. I removed my .zshrc and it works as expected.
> >
> > Thanks for the hint! Time to figure out what poorly written part of my
> > .zshrc is to blame.
>
> It will probably be something involving print -P and \a or \007 in
> something named preexec. If you change $1 in that to \$1 it is more
> likely to work,


Probably = 100% likely.


> though it's of course hard to say without seeing the
> particular code.


For fun, and full disclosure, here is the code:

preexec () {
    case $TERM in (xterm*|screen*|tmux*|rxvt)
        print -Pn "\e]0;%(!.-=*[ROOT]*=- | .)%n@%m:%y : $1\a"
    esac
}

to which I've changed $1 to \$1 and it fixes the issue.

Thanks for the help, Mikael! It is very appreciated!

-m

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Re: inconsistency between bash and zsh subshells

[Dominik Vogt]

On Mon, May 23, 2022 at 11:55:09AM -0500, Matt Zagrabelny wrote:
> zsh$ rm -f /tmp/FOO
> zsh$ ls /tmp/FOO 2> /dev/null || echo "no /tmp/FOO"
> no /tmp/FOO

> zsh$ echo | while read LINE; do IP=$(echo $LINE | cut -d ' ' -f 1); if [ -n
> "$IP" ]; then echo FOO; FOO=$(touch /tmp/FOO); else echo BAR; fi; done; ls
> /tmp/FOO 2> /dev/null || echo "no /tmp/FOO"

This output cannot have been generated by the above command:

> BAR
> /tmp/FOO     <--- ???

Ciao

Dominik ^_^  ^_^

--

Dominik Vogt