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Date: Thu, 6 Apr 2023 10:03:23 +0200
To: cygwin AT cygwin DOT com
Subject: Re: bash shell script: recently running, now failing
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From: Corinna Vinschen via Cygwin <cygwin AT cygwin DOT com>
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On Apr  6 04:43, Fergus Daly via Cygwin wrote:
> I have a "hash bang" bash shell script i.e. first line
> #! /bin/sh
> or equivalently
> #! /bin/bash
> For various reasons I want this file to be identified as binary so its second line
> is the single character null \x00 showing up in some editors e.g. nano as
>  ^@
> This does not prevent the script from running to a successful conclusion.
> Or not until recently. Now the script fails with
> /home/user/bin/file.old.sh: cannot execute binary file
> Q1 - was bash recently updated? Would this explain the changed behaviour?

bash was recently updated from 4.4.12 to 5.2.15.

The behaviour is the same in bash on Linux.  Take this file with
a \0 in line 2:

  $ cat -v x.sh
  #! /bin/bash
  ^@
  echo foo
  $ bash --version | head -1
  GNU bash, version 5.2.15(1)-release (x86_64-redhat-linux-gnu)
  $ ./x.sh
  ./x.sh: ./x.sh: cannot execute binary file

While dash on Linux runs the script:

  $ sed -i -e 's/bash/dash/' x.sh
  $ ./x.sh
  foo

> Q2 - if so, is this newly introduced "glitch" known and presumably
> intended? Or an unintended consequence that will be retracted in a
> later update? 

Bash follows the POSIX standard:
https://pubs.opengroup.org/onlinepubs/9699919799/utilities/sh.html#tag_20_117_07
https://pubs.opengroup.org/onlinepubs/9699919799/basedefs/V1_chap03.html#tag_03_403

So I don't expect this will change any time soon.

> Q3 - at 1/8 the size of bash and sh, I am not at all sure of the role and reach of dash.

Dash is a minimal shell with no bells and whistles.  It loads ands runs
slightly faster than bash.  If you only need bare minimum bourne shell
behaviour, it's a good choice for scripts.


Corinna

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