test if script called by cron

[Polytropon]

On Mon, 16 Sep 2013 23:28:17 -0400, kpneal at 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, ...