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Re: How to detect bash?


From: Stephane Chazelas
Subject: Re: How to detect bash?
Date: Tue, 10 Oct 2006 23:33:01 +0100
User-agent: Mutt/1.5.6i

On Tue, Oct 10, 2006 at 05:12:07PM -0500, mwoehlke wrote:
> Dave Rutherford wrote:
> >On 10/10/06, mwoehlke <address@hidden> wrote:
> >>Anyone have any clever, VERY reliable tricks for detecting if the
> >>current shell is bash?
> >
> >Well, I don't know if it's clever, but how about:
> 
> Oh, my... Where do I *start*?
> 
> >$ if [ "${SHELL//*/bash}" = "bash" ]; then echo y; fi
> 
> $ echo $SHELL
> /bin/sh
> $ echo $BASH
> /bin/bash
> $ foo
> bash: foo: command not found
> 
> There is *ABSOLUTELY* no guarantee that $SHELL correctly points to bash, 
> or that $SHELL is even remotely correct for that matter. This is /worse/ 
> than relying on $BASH.
> 
> But it does bring up an interesting possibility:
> [ "`/dev/null 2>&1`" = "bash: /dev/null: Permission denied" ]
[...]

You quest looks a bit pointless to me. What prevents the user to
edit a copy of your script to remove the check anyway?

$ zsh -c 'echo "`/dev/null 2>&1`"' bash
bash: /dev/null: Permission denied

$ zsh
$ ARGV0=bash ash -c 'echo "`/dev/null 2>&1`"; echo $BASH'
bash: /dev/null: Permission denied

$ echo '/dev/null(){echo "bash: /dev/null: Permission denied"}' \
>   >> ~/.zshenv
$ zsh -c 'echo "`/dev/null 2>&1`"'
bash: /dev/null: Permission denied

And whatever check you do can be worked around in a way or
another.

-- 
St├ęphane




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