ITEM: AF4903L

Running crontab entry first Sunday of each month

Question:

Env:    AIX 3.2.5

Desc:  Customer wants to setup a cron job that will run on the first
       Sunday of each month. The syntax he wants to use in the crontab
       file is:

         00 20 1-7 * 0 file_to_run

       He is looking at the crontab man page and it reads:

       If both the day of the month and day of the week fields are 
       specified as an element or list, but the day of the week is an 
       asterisk, both lists are matched.

Action: 

The customer's example actually matches the following crontab rule:

  If either the month of the year or day of the month field is 
  specified as an element or list and the day of the week field 
  is also specified as an element or list, then any day matching 
  either the day of the week field, or month of the year and day 
  of the month fields are matched.

The customer should be seeing his script run on the first through 
seventh of every month as well as for every Sunday.

I tested this scenario and the crontab entry suggested by the
customer does indeed work this way.  Here is the test case I used:

crontab:

  00 8 1-7 * 0 /tmp/file_to_run

file_to_run:

  echo "Running at `date`" >> /tmp/file_to_run.file

I then manipulated the date through the month of February and
this is the output from /tmp/file_to_run.file:

  Running at Wed Feb  1 08:00:00 CST 1995
  Running at Thu Feb  2 08:00:00 CST 1995
  Running at Fri Feb  3 08:00:01 CST 1995
  Running at Sat Feb  4 08:00:00 CST 1995
  Running at Sun Feb  5 08:00:01 CST 1995
  Running at Mon Feb  6 08:00:01 CST 1995
  Running at Tue Feb  7 08:00:00 CST 1995
  Running at Sun Feb 12 08:00:01 CST 1995
  Running at Sun Feb 19 08:00:00 CST 1995
  Running at Sun Feb 26 08:00:01 CST 1995

I then tried the following workaround.  In this test case the 
crontab entry is changed to run on every Sunday.  Then the script
is modified to test the date and see if it is the first through 
the seventh.  This worked just as the customer would like.  Here
is the test case:

crontab:

  00 8 * * 0 /tmp/file_to_run2

file_to_run2:

  if [ `date +%d` -lt 8 ]
  then
    echo "Running at `date`" >> /tmp/file_to_run.file2
  else
    echo "Not Running at `date`" >> /tmp/file_to_run.file2
  fi

Again, I manipulated the date through the month of February 
and got the following results in /tmp/file_to_run.file2:

Running at Sun Feb  5 08:00:01 CST 1995
Not Running at Sun Feb 12 08:00:00 CST 1995
Not Running at Sun Feb 19 08:00:00 CST 1995
Not Running at Sun Feb 26 08:00:00 CST 1995



Support Line: Running crontab entry first Sunday of each month ITEM: AF4903L

Dated: January 1995 Category: N/A

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