Re: Unix - scheduling - I know this, it's a UNIX system

• Brian_P_MacLean_at_eFunds.Com on 07/03/02 14:13:30 -0800

>
> This will run the job every 28 daze at 1am. If that's not exactly the
> definition of every 4th week let me know and I'll work something out. Also
> note that you will have an anomaly at the end of leap years.
>
>
> 0 1 * * * /usr/bin/ksh -c '[ $(($(date '+\%j') \% 28)) -eq 0 ] &&
> /path/to/my/job/the_job'

       %j day of year (001..366)

Two problems are not adjusting the initial start date (simple enough, adding a constant) and 365 % 28 != 0. The last will give you an extended period once per year. The only reliable way to handle this requries gnu date, which has %s == system time in GMT:     

    [ $(( ($(date +%s) + $INITIAL_DATE_OFFSET) % 2419200 )) -eq 0 ] && /blah;

Is a bit grimy but works. The wallclock time may shift slightly during the DST correction but the basic interval works.

The one-second resolution can cause problems if crond doesn't run exactly on the minute; this can be corrected by taking the integer portion after dividing by 60 and comparing that.

At which point it's better to give up on cron entirely and use at, which does all of this mess for you and handles cron outages also (which the above doesn't).

--
Steven Lembark                              2930 W. Palmer
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