Can't access shell variable in crontab configuration

Question

I have problem in accessing a shell variable while running cron job. Actually i created a job which prints two shell variable values into a env.output file.

I am writing cron job using command $ crontab -e (without sudo user).

My crontab configuration file looks like this:-

# varibales
SHELL=/bin/bash
PATH=/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin:
     /usr/games:/usr/local/games
MAILTO=abc@xyz.com
HOME=/home/ubuntu
JOBS_PATH=${HOME}/cronjobs

# Jobs
* * * * * echo "$HOME and $JOBS_PATH" >> ${HOME}/env.output 2>&1

So, now when i see the contents of file env.output , i get this output

/home/ubuntu and ${HOME}/cronjobs

which is not expected i assumed.

I want my output should looks like this:-

/home/ubuntu and /home/ubuntu/cronjobs

Suggest me some way to handle this issue.

Answer 1

I have problem in accessing a shell variable

HOME as defined at the top of a crontab is not a shell variable, is an environment variable.

You can't reference environment variables at the top of a crontab, as no shell processes them and thus they're not expanded (and interpreted literally).

You'll have to set JOBS_PATH manually:

# ...
JOBS_PATH=/home/ubuntu/cronjobs
# ...

Answer 2

This is a limitation of the cron daemon. See this from the manpage of crontab:

The value string is not parsed for environmental substitutions or replacement of variables, thus lines like:

     PATH = $HOME/bin:$PATH

will not work as you might expect.

You can do a workaround, since bash treats the tilde (~) as substitution of $HOME. Therefore use:

JOBS_PATH=~/cronjobs