Re: OT: Linux Interview Questions
On Fri, Mar 16, 2007 at 01:16:46AM +0200, Atis wrote:
> [snip]
> >> >00 06 * * * [ `date -d tomorrow +%d` -eq '01' ] && /the/script
> >> >
> >> >for 6:00 AM on the last day of each month
>
> [snip]
> >when you have multiple commands on a line with && between them, it
> >executes them sequentially as long as none of them fail, IOW so long
> >as they return 0. the [ ... ] is the 'test' command and it tests the
> >statement inside the brackets and returns a 0 if the statement is
> >true. if its false (i.e. `date -d tomorrow +%d` is '02') then it will
> >return a 1 and the whole statement will fail.
>
> Damn, so this is just a cheat, as the actual command is
> [ `date -d tomorrow +%d` -eq '01' ] && /the/script
> and it will be executed every day..
>
Yes its a cheat. The correct answer is that having __cron__ run
something only on the last day of a month is impossible. Cron itself
runs every minute of every day. I guess any type of alarm clock has to
run at intervals equal to its granularity. A wall clock tics every
second for example.
Personally, I find bash scripting very cryptic and I don't mean that as
a compliment to bash. If I had to run a command on the last day of the
month I would just write a Python script that did this kind of testing
and have it run as part of cron.daily.
Doug.
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