Date: Fri, 28 Oct 2016 09:34:26 +0100 From: Arthur Chance <freebsd@qeng-ho.org> To: Tim Daneliuk <tundra@tundraware.com> Cc: FreeBSD-Questions <freebsd-questions@freebsd.org> Subject: Re: Interesting $0 Problem Message-ID: <516bc76f-f14c-e9a5-a246-2e915a5369ce@qeng-ho.org> In-Reply-To: <b859f7a3-51d1-06f4-e793-332edd212068@tundraware.com> References: <b859f7a3-51d1-06f4-e793-332edd212068@tundraware.com>
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On 28/10/2016 02:30, Tim Daneliuk wrote:
> I was fidding with some shell code today and discovered it was breaking
> because $0 was returning "-/usr/local/bin/bash". Why is there a leading
> dash here? I've not seen that before.
>
This is from "man sh" in the "Invocation" section but presumably bash is
mimicking the standard behaviour.
> When first starting, the shell inspects argument 0, and if it begins
> with a dash (‘-’), the shell is also considered a login shell. This
> is normally done automatically by the system when the user first
> logs in.
And in the source code for /usr/bin/login
/*
* Login shells have a leading '-' in front of argv[0]
*/
Prepending a dash to a login shell has been standard behaviour since the
BSD days at least. I think it was in version 6 of the original Bell Labs
Unix as well, but after three and a half decades my memories for such
details are a bit hazy. Anyway, it's a standard marker.
--
Schrödinger's cat had 18 half lives.
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