From owner-freebsd-questions  Sat Aug 28  9:44:55 1999
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Date: Sat, 28 Aug 1999 15:55:08 +0100
From: Ben Smithurst <ben@scientia.demon.co.uk>
To: big-sky@altavista.net
Cc: freebsd-questions@freebsd.org
Subject: Re: roots shell
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References: <19990819222133.B12658@lithium.scientia.demon.co.uk> <000301bef156$a12cc5a0$0201010a@cmr.net>
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Mark Einreinhof wrote:

> I like your paranoia... could you explain what that line means?

Of course. All it does is run `bash --version`, throughing its output
away, which will just make sure you *can* actually run it. If that
succeeds, it will run bash properly as a login shell for you.  The test
-x command just makes sure the file has the executable flag set. Normally,
that should be enough, but if you want to be paranoid you should check for
example that a library isn't missing.

allow me to demonstrate:

root@magnesium:~# bash --version
/usr/libexec/ld-elf.so.1: Shared object "libc.so.3" not found
root@magnesium:~# echo $?
1
root@magnesium:~# [ -x /usr/local/bin/bash ]
root@magnesium:~# echo $?
0
root@magnesium:~# 

As you can see, the [ -x ] says that bash *can* be executed, when in
fact, it cannot, as running it demonstrates: a library is missing. If
you do exec bash when a library is missing, your current shell will
vanish, and take you back to a login prompt, or in my case, my normal
account which I had su'd from (yes, I did have another root window open
to put libc.so.3 back in place :-)

> Can I place it into the .login file as written minus quotes,
> "/usr/local/bin/bash --version >/dev/null 2>&1 && exec /usr/local/bin/bash"

Yes.

> or do I need the [ -x like the earlier line was written?

No.

-- 
Ben Smithurst            | PGP: 0x99392F7D
ben@scientia.demon.co.uk |   key available from keyservers and
                         |   ben+pgp@scientia.demon.co.uk


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