Date: Tue, 17 Sep 2013 05:38:26 +0200 From: Polytropon <freebsd@edvax.de> To: kpneal@pobox.com Cc: Paul Macdonald <paul@ifdnrg.com>, freebsd-questions@freebsd.org Subject: Re: test if script called by cron Message-ID: <20130917053826.5a5c7ed3.freebsd@edvax.de> In-Reply-To: <20130917032817.GA17509@neutralgood.org> References: <5236EB03.7040001@ifdnrg.com> <20130916140504.739fd28f.freebsd@edvax.de> <20130917032817.GA17509@neutralgood.org>
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On Mon, 16 Sep 2013 23:28:17 -0400, kpneal@pobox.com wrote:
> On Mon, Sep 16, 2013 at 02:05:04PM +0200, Polytropon wrote:
> > On Mon, 16 Sep 2013 12:26:59 +0100, Paul Macdonald wrote:
> > > Is there a simple way of testing whether a given script was called via cron,
> > >
> > > I'd rather find a solution that would work from within the script rather
> > > than setting an environment variable in the crontab.
> >
> > I'd suggest the script creates a file (lock file or,
> > much easier, just a simple normal file) at its beginning:
> >
> > #!/bin/sh
> > /usr/bin/touch /tmp/scriptrun
> > # ... your script content here ...
>
> Wouldn't the lockf command be better than touch? That way you get the
> condition code telling you whether or not the script is already running.
Yes, it would probably be better in this case. This, in
combination with the suggestion of "test-t 0" to check
if the script has been interactively called or not, looks
like a better solution.
However, the intial question does not make fully sure (at
least to me as a non-native speaker) if the intention is
(a) to check _if_ the script has been run via cron, or
(b) to check if the script has been run via _cron_. :-)
> > Of course you would have to manually remove that file
> > after you have verified its existence and content.
>
> If you use lockf as a drop-in replacement for touch then, yes, you'll
> need to keep the lock file until removing it at the end of the script.
Depends. Let's say the script is scheduled at 3:00 and will
finish in about half an hour. The "evidence file" will only
be visible from 3:00 to ca. 3:30, so removing the "evidence
file" after the script has finished could lead to a false-negative
result ("has not been run"). This is also true for the more
simple solution using the touch command (no rm call at the
end of the script).
--
Polytropon
Magdeburg, Germany
Happy FreeBSD user since 4.0
Andra moi ennepe, Mousa, ...
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