Can't use `source` from cron?

Question

I'm setting up a docker container which requires a cronjob to do a backup using awscli.

I'm having a problem with the cron job being able to access the environment variables of the docker container. As I work around on startup I print all environment variables to a file printenv > /env.

When I try to use source from the cron job (I have tried both directly in crontab and in a script called by crontab) it doesn't seem to work.

I made a simplified version of my project to demonstrate the issue (including rsyslog for logging):

Dockerfile:

FROM debian:jessie

# Install aws and cron
RUN apt-get -yqq update
RUN apt-get install -yqq awscli cron rsyslog

# Create cron job
ADD crontab /etc/cron.d/hello-cron
RUN chmod 0644 /etc/cron.d/hello-cron

# Output environment variables to file
# Then start cron and watch log
CMD printenv > /env && cron && service rsyslog start && tail -F /var/log/*

crontab:

# Every 3 minutes try to source /env and run `aws s3 ls`.
*/3 * * * * root /usr/bin/env bash & source /env & aws s3 ls >> /test 2>&1

When I start the container I can see /env was created with my variables but it never gets sourced.

Answer 1

First of all, the command's (well, shell builtin's) name is source. Unless you have written a script called source and put it in /, you want source and not /source.

The next issue is that cron usually uses whatever you have as /bin/sh and source is a bashism (or other such more complex shells). The portable, POSIX-compliant command for sourcing a file is .. So, try that instead of source:

*/3 * * * * root /usr/bin/env bash & . /env & aws s3 ls >> /test 2>&1

Also, I don't quite understand what that is supposed to be doing. What's the point of starting a bash session and sending it to the background? If you want to use bash to run the subsequent commands, you'd need:

*/3 * * * * root /usr/bin/env bash -c '. /env && aws s3 ls' >> /test 2>&1

I also changed the & to && since sourcing in the background is pointless as far as I can see.

Answer 2

You can use . since as terdon's answer already mentioned that cron uses /bin/sh by default and doesn't recognize source command sometimes.

I wanted to add one more thing: you can't source file and use that in second command, so something like this might not work:

* * * * * source ~/.bash_profile
* * * * * do some stuff with bash_variables

Because each line is session itself so sourced variables in first command will not be available in later commands. You would have to do something like this:

* * * * * source ~/.bash_variable && do some stuff with bash_variables