Random file creation in zsh shell.

Random file creation in zsh shell.

[LitHack]

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There is a way to create a random file in zsh shell by which we could hide
any of our data in it.

Command: <>=()

Explanation: By running this command we can create a random file in /tmp
directory and each time it create new file with random name having "zsh" in
front of them. According to me this is bug.

Thanks.

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Fwd: Random file creation in zsh shell.

[LitHack]

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---------- Forwarded message ---------
From: LitHack <lithack0@gmail.com>
Date: Sat, Jun 17, 2023, 7:33 AM
Subject: Random file creation in zsh shell.
To: <zsh-workers@zsh.org>


There is a way to create a random file in zsh shell by which we could hide
any of our data in it.

Command: <>=()

Explanation: By running this command we can create a random file in /tmp
directory and each time it create new file with random name having "zsh" in
front of them. According to me this is bug.

Thanks.

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Re: Random file creation in zsh shell.

[Roman Perepelitsa]

On Sat, Jun 17, 2023 at 4:04 AM LitHack <lithack0@gmail.com> wrote:
>
> There is a way to create a random file in zsh shell by which we could hide any of our data in it.
>
> Command: <>=()

I found this surprising.

    % =true < =()
    % ls /tmp/zsh*
    /tmp/zshMw5YZq

Is it expected for `=true < =()` to leave a temporary file behind?

With the builtin `true` the behavior matches my expectation:

    % true < =()
    % ls /tmp/zsh*
    zsh: no matches found: /tmp/zsh*

Another example that leaves a temporary file behind:

    % ( exec true ) < =()

All of these work as expected, meaning that they don't leave a
temporary file behind:

    % () { =true } < =()
    % ( =true ) < =()
    % ( true ) < =()

Roman.

Re: Random file creation in zsh shell.

[Bart Schaefer]

On Fri, Jun 16, 2023 at 11:36 PM Roman Perepelitsa
<roman.perepelitsa@gmail.com> wrote:
>
> On Sat, Jun 17, 2023 at 4:04 AM LitHack <lithack0@gmail.com> wrote:
> >
> > There is a way to create a random file in zsh shell by which we could hide any of our data in it.
>
> Is it expected for `=true < =()` to leave a temporary file behind?

When an =(...) temp file is created, the parent shell assigns removal
to the child job, which is supposed to happen when the job exits.  In
the case of a shell function or builtin, this works as expected.  In
the case of an external command or a subshell that performs a "tail
call optimization" like your "( exec true )" example, the thread
that's meant to remove the temp file is replaced by a new process and
the exit-handler that would remove the file is lost.

I've spent quite a while on and off in the past prodding at the code
in exec.c to try to convince it that when there is a temp file present
it should skip the execve() and instead fork()/wait() to be able to
remove the file at the end, but have never got it to work without
breaking something else.

Re: Random file creation in zsh shell.

[Bart Schaefer]

On Fri, Jun 16, 2023 at 7:04 PM LitHack <lithack0@gmail.com> wrote:
>
> There is a way to create a random file in zsh shell by which we could hide any of our data in it.

There are lots of ways to do this if you are able to run commands in
the shell.  Who is the "our" that is "hiding" data, and why does that
matter?