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Chapter 10: Scripting
• month is a number between 1 and 12 or a name such as February.
•
day_of_week is a number between 0 and 7 (0 or 7 is Sunday, 6 is Saturday) or a
name such as
Tuesday.
•
day_of_month and day_of_week are ORed together, which may cause surprises.
For instance, if each field contains a
1, cron will execute the command in Janu-
ary as well as on Mondays. Usually, the crontab line puts a specific value in only
one of these fields.
• In any field, a value means an exact match; for instance, a
1 in the month field
means only January.
• An asterisk (
*) means any value.
• Two values separated by a hyphen indicate a range. Thus,
11-12 in the month
field means November through December.
• To specify more than one value, separate the values with commas. A
month list of
2,3,5-6 means February, March, and May through June.
•Astep modifier may follow values and a slash (
/), and it indicates how many
units to increment between values. A
month value of */3 means every third
month. A
month value of 4-9/2 means months 4, 6, and 8.
The shell executes the command, so it can use the features mentioned in this chap-
ter. Some examples using direct commands rather than scripts are:
5 * * * * rm /tmp/*.gif # remove all GIF files every 5 minutes
5 * * * * rm -v /tmp/*.gif >> /tmp/gif.log # the same, logged
When cron runs the command, it emails its standard output and standard error to
the owner of the crontab ...