From mboxrd@z Thu Jan  1 00:00:00 1970
From: Paul Smith <paul@mad-scientist.net>
Subject: Re: Tests [ 0 -eq $UID ] don't work as in bash
Date: Wed, 07 Sep 2016 11:55:00 -0400
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To: Andrey Voropaev <voropaev.andrey@gmail.com>, dash@vger.kernel.org

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.