Many commands require environment variables to be set properly for execution. The cron command sets the SHELL variable to "/bin/sh" and also sets LOGNAME and HOME from the values in /etc/passwd. If other variables are required, they can be defined in the crontab. These can be defined for all tasks or individually for a single task.

If the MAILTO environment variable is defined, cron will send the output of the command to that user via an e-mail.

The crontab defines environment variables by inserting a line with a variable assignment statement in the user's cron table.

The following crontab defines an http_proxy environment variable to use a proxy server for Internet interactions:

    http_proxy=http://192.168.0.3:3128
    MAILTO=user@example.com
    00 * * * * /home/slynux/download.sh

This format is supported by vixie-cron, used in Debian, Ubunto, and CentOS distributions. For other distributions, environment variables can be defined on a per-command basis:

    00 * * * * http_proxy=http:192.168.0.2:3128;   
    /home/sylinux/download.sh