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Date: Thu, 3 Dec 2015 13:49:29 +0000
From: Stephane Chazelas <stephane.chazelas@gmail.com>
To: zsh-workers@zsh.org
Subject: Re: a way to get the value of the -c option
Message-ID: <20151203134929.GA9581@chaz.gmail.com>
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References: <20151203115449.GA19846@zira.vinc17.org>
 <20151203124554.3b93281f@pwslap01u.europe.root.pri>
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User-Agent: Mutt/1.5.21 (2010-09-15)

2015-12-03 12:45:54 +0000, Peter Stephenson:
> On Thu, 3 Dec 2015 12:54:49 +0100
> Vincent Lefevre <vincent@vinc17.net> wrote:
> > zsh should provide a way to get the value of the -c option. Under
> > Linux, one can look at /proc/$$/cmdline, but I think that it would
> > be better to get this information in an OS-independent way.
[...]
> +vindex(ZSH_CMD_ARG)
> +item(tt(ZSH_CMD_ARG))(
> +If the shell was started with the option tt(-c), this contains
> +the argument passed to the option.  Otherwise it is not set.
[...]

Note that bash calls it $BASH_EXECUTION_STRING

It could be useful to have zsh's equivalent being
$ZSH_EXECUTION_STRING.

Note that bash doesn't clear it from the environment and doesn't
unexport it:

$ echo set | env BASH_EXECUTION_STRING=zzz  bash -s | grep zzz
BASH_EXECUTION_STRING=zzz

$ BASH_EXECUTION_STRING=zzz bash -c 'echo $BASH_EXECUTION_STRING; echo set | bash' | grep EXE
echo $BASH_EXECUTION_STRING; echo set | bash
BASH_EXECUTION_STRING='echo $BASH_EXECUTION_STRING; echo set | bash'

Now, if *you* export it to the environment, you're the one to
blame. In the case of bash, it's also affected by the -a
option:

$ bash -ac env | grep BASH
BASH=/bin/bash
BASH_EXECUTION_STRING=env
BASH_VERSION=4.3.11(1)-release

env -i zsh -ac env

shows a lot of variables as well. The intent with "-a" is that
all *newly-declared* (after "set -a" is issued) variables are
automatically exported.  It's arguable whether those internal
variables should also be exported or not when the shell is
called with -a. mksh bash zsh export them, dash ksh93 yash
don't.

Cheers,
-- 
Stephane