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From: Stephane Chazelas <stephane.chazelas@gmail.com>
To: Paul Smith <paul@mad-scientist.net>
Cc: Andrey Voropaev <voropaev.andrey@gmail.com>, dash@vger.kernel.org
Subject: Re: Tests [ 0 -eq $UID ] don't work as in bash
Date: Wed, 7 Sep 2016 21:02:18 +0100	[thread overview]
Message-ID: <20160907200218.GA28963@chaz.gmail.com> (raw)
In-Reply-To: <1473263700.7265.3.camel@mad-scientist.net>

2016-09-07 11:55:00 -0400, Paul Smith:
> On Wed, 2016-09-07 at 16:44 +0200, Andrey Voropaev wrote:
> > if [ 0 -eq $UID ]
> 
> The variable UID is not defined to be automatically set by the shell in
> POSIX; having it set is a bash extension.  dash doesn't set it
> automatically for you.
> 
> You'll have to set it yourself:
> 
>   UID=$(id -u)
> 
> Also you should quote variable references, in general:
> 
>   if [ 0 -eq "$UID" ]
> 
> Be sure that if your scripts rely on bash-isms you start them with
> #!/bin/bash and if you don't want them to rely on bash-isms, you start
> them with #!/bin/sh.
[...]

Note that both zsh and bash have it, both from the start, both
copied from tcsh ($uid in tcsh).

In zsh, you can also set UID (and USERNAME and EUID, and GID...)
to change your uid (assuming you have the permission to do so).

$ sudo zsh -c 'id; UID=1000; id; UID=0'
uid=0(root) gid=0(root) groups=0(root)
uid=1000(chazelas) gid=0(root) groups=0(root)
zsh:1: failed to change user ID: operation not permitted

In bash, UID is read-only.

-- 
Stephane

      reply	other threads:[~2016-09-07 20:02 UTC|newest]

Thread overview: 3+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2016-09-07 14:44 Andrey Voropaev
2016-09-07 15:55 ` Paul Smith
2016-09-07 20:02   ` Stephane Chazelas [this message]

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