How can I run a cron command with existing environmental variables?

In the crontab, before you command, add . $HOME/.profile. For example:

0 5 * * * . $HOME/.profile; /path/to/command/to/run

Cron knows nothing about your shell; it is started by the system, so it has a minimal environment. If you want anything, you need to have that brought in yourself.

Another option, which I find easier, is to run the script with cron and have the environment in the script.

In crontab -e file:

SHELL=/bin/bash

*/1 * * * * $HOME/cron_job.sh

In cron_job.sh file:

#!/bin/bash
source $HOME/.bash_profile
some_other_cmd

Any command after the source of .bash_profile will have your environment as if you logged in.

Another option, which I find easier, is to run the script with cron and tell bash to login (hence using /etc/profile.d/... environment definitions)

In crontab -e file:

*/1 * * * * bash -l -c './cron_job.sh'
*/1 * * * * bash -l -c 'php -f ./cron_job.php'

Any command after the source of .bash_profile will have your environment as if you logged in.