Cron Environment Variable Settings
Each environment variable line consists of a
variable name, an equal sign (=), and a value.
Values that contain spaces need to be
enclosed within quotes.
The following are some examples of
environment variable settings:
color = red
title = ‘My Life in a
Nutshell’
It is important to remember that variable names
are case sensitive and that system variables are
usually defined with upper case names, while
user defined variables are defined with lower
case names.
Crontab Command Line Tips
Each crontab command line is comprised of six
positional fields specifying the time, date and
shell script or command to be run.
The format of the crontab command line is
described in Table 11.2 below:
|
Field
|
Minute
|
Hour
|
Day of Month
|
Month
|
Day of Week
|
Command
|
|
Valid values
|
0-59
|
0-23
|
1-31
|
1-12
|
0-7
|
Command path/command
|
Table 11.2:
Crontab
Command Line Format
Each of these fields can contain a single
number, a range of numbers indicated with a
hyphen (such as 2-4), a list of specific values
separated by commas (like 2,3,4) or a
combination of these designations separated by
commas (such as 1,3-5).
Any of these fields may also contain an
asterisk (*) indicating every possible value of
this field.
This can all get rather confusing, so
here are a few examples that are all part of the
same crontab file.
It has been broken up so as to explain
each entry individually.
# Use the Korn Shell for
all shell scripts
SHELL=/bin/ksh
This sets the default shell for these cron
scripts by setting the SHELL environment
variable.
#**********************************************************
# Run the Weekly file
cleanup task at
6:00AM
every Monday
# and send any output to a
file called cleanup.lst in the
# /tmp directory
#**********************************************************
00 06 * * 1
/home/terry/cleanup.ksh > /tmp/cleanup.lst
This entry will run the script
cleanup.ksh at 0 minutes past the
hour of 6:00 am, every day of the month, every
month of the year, but only on Mondays.
This illustrates that for a
crontab to execute, all of the conditions
specified must be met. So even though it was
stated that the designation is every day of the
month by making the third field a wildcard, the
day also has to meet the final condition that
the day is a Monday.
#**********************************************************
# Run the Weekly
Management Report every Monday at
7:00 AM
# and save a copy of the
report in my /home directory
#**********************************************************
00 07 * * 1
/home/terry/weekly_mgmt_rpt.ksh wprd >
/home/terry/weekly_mgmt_rpt.lst
This entry is very similar but will execute at
7:00 am.
Since the hour is in 24-hour format
(midnight is actually represented as 00), then
07 represents 7:00 a.m.
Again, this entry will only be run once a
week.
#**********************************************************
# Weekly Full Backup - run
every Sunday at
1:30AM
#**********************************************************
30 01 * * 0
/home/terry/full_backup.ksh wprd > /tmp/full_backup.lst
Here this script is specified to be run at 30
minutes past the hour, the first hour of the
day, but only on Sundays.
Remember that in the day of the week
column, Sunday can be represented by either 0 or
7.
#**********************************************************
# Nightly Incremental
Backup - run Monday-Saturday at 1:30AM
#**********************************************************
30 01 * * 1-6
/home/terry/incr_backup.ksh
> /tmp/incr_backup.lst
In this crontab entry, it shows the same
indication for hour and minute as the last
entry, but a range has been specified for the
day of the week.
The range 1-6 will cause the
incr_backup.ksh to be executed at
1:30 every morning from Monday through Saturday.
#**********************************************************
# Low disk space alert ...
run every 15 minutes, sending
# alerts to key
individuals via e-mail
#**********************************************************
00,15,30,45 * * * *
/home/terry/free_space.ksh > /tmp/free_space.lst
This entry has minutes separated by a comma
indicating that it should be run at each of the
indicated times.
Since all the other fields are wildcards
(*), the entry will be run on the hour (00), 15
minutes past the hour, 30 minutes past the hour
and 45 minutes past the hour.
#**********************************************************
# Lunch Time Notification
- run Monday-Friday at
Noon
-
# sends a message to all
users indicating it's lunch time
#**********************************************************
00 12 * * 1-5
/home/terry/lunch_time.ksh wprd > /tmp/lunch_time.lst
This lunch reminder is set up to run at 12:00
p.m. Monday through Friday only.
