The crontabThe crontab
command has several options.
Option |
Purpose |
-e |
edit the current crontab file using
the text editor specified by the EDITOR
environment variable or the VISUAL
environment variable |
-l |
list the current crontab file |
-r |
remove the current crontab file |
-u |
specifies the user?s crontab to be
manipulated. This is usually used by
root to manipulate the crontab of other
users or can be used by you to correctly
identify the crontab to be manipulated
if you have used the su command to
assume another identity. |
Options for the crontab
command
crontab
can also accept a file
name and will use the specified file to create
the crontab file. Many users prefer to use this
option rather than the crontab -e
command because it provides a master file from
which the crontab is built, thus providing a
backup to the crontab. The following example
specifies a file called mycron.tab to be used as
the input for crontab.
$ crontab mycron.tab
Here?s how you would use the crontab ?l
command to view the current cron entries for the
logged in user.
$ crontab -l
#**********************************************************
# 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
#**********************************************************
# 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
Now if we wanted to delete all the entries in
the crontab we can use the ?r option.
$ crontab -r
The Format of the crontab File
The crontab file consists of a series of
entries specifying what shell scripts to run and
when to run it. It is also possible to document
crontab entries with comments. Lines which have
a pound sign (#) as the first non-blank
character are considered comments. Blank lines
are completely ignored. Comments cannot be
specified on the same line as cron command
lines. Comments must be kept on their own lines
within the crontab.
There are two types of command lines that can
be specified in the crontab: environment
variable settings and cron commands. The
following sections will provide more detail on
these two types of crontab entries.