cron - Variables in crontab?

Question

How can I store variables in my crontab? I realize it's not shell but say I want to have some constants like a path to my app or something?

Answer 1

In Vixie cron, which is possibly the most common, you can do this almost exactly like a shell script.

VARIABLE=value
PATH=/bin:/path/to/doathing
0 0 * * * doathing.sh $VARIABLE

The man page says:

An active line in a crontab will be either an environment setting or a cron command. An environment setting is of the form,

     name = value

where the spaces around the equal-sign (=) are optional, and any subsequent non-leading spaces in value will be part of the value assigned to name. The value string may be placed in quotes (single or double, but matching) to preserve leading or trailing blanks. The name string may also be placed in quote (single or double, but matching) to preserve leading, trailing or inner blanks.

You can tell if you have Vixie cron by checking the man page for crontab; the author will be Paul Vixie. Different crons may or may not support this (BusyBox's cron for example, does not), in which case your best option is to wrap your command in a shell script and run that script from cron instead. In fact, this is a good thing to do for anything complicated.