Where can I set environment variables that crontab will use?

Environment variables are typically set in shell configuration files like .bash_profile, .bashrc (Ubuntu), or .zshrc (macOS). However, crontab runs in a minimal environment and doesn't automatically load these shell configuration files, making environment variables unavailable to cron jobs.

Understanding the Problem

Let's examine a typical shell configuration file with environment variables −

immukul@192 dir1 % cat ~/.bash_profile
export JAVA_HOME=$(/usr/libexec/java_home)
export PATH=$PATH:/usr/local/node/bin
export GOROOT=/usr/local/go
export GOPATH=/Users/immukul/go_projects

These variables work perfectly in a normal terminal session −

echo $GOROOT

/usr/local/go

However, when you create a cron job, these variables are not available because cron operates with a minimal environment that doesn't source your shell configuration files.

Solutions for Making Environment Variables Available to Crontab

Method 1: Using Login Shell in Script

The most common approach is to use the -l (login) flag with bash in your cron script. First, create your cron job −

crontab -e

Add the following line to run your script every minute −

* * * * * /path/to/sample.sh

In your sample.sh script, use the login shell −

#!/bin/bash -l

echo "PATH: $PATH"
echo "GOROOT: $GOROOT"
for f in *.txt; do mv "$f" "${f// /_}"; done

The #!/bin/bash -l shebang tells the script to run as a login shell, which loads your .bash_profile and makes environment variables available.

PATH: /usr/local/bin:/usr/bin:/bin:/usr/sbin:/sbin:/usr/local/go/bin:/Library/Apple/usr/bin
GOROOT: /usr/local/go

Method 2: Setting Variables Directly in Crontab

You can define environment variables directly in your crontab file −

JAVA_HOME=/usr/lib/jvm/java-11-openjdk
GOROOT=/usr/local/go
PATH=/usr/local/bin:/usr/bin:/bin:/usr/sbin:/sbin

* * * * * /path/to/sample.sh

Method 3: Sourcing Configuration Files in Script

Explicitly source your shell configuration within the script −

#!/bin/bash

source ~/.bash_profile

echo "Using GOROOT: $GOROOT"
# Your script commands here

Comparison of Methods

Conclusion

Cron jobs run in a minimal environment without access to your shell's environment variables. The most effective solution is using #!/bin/bash -l in your scripts to load the login shell environment. For production systems, consider setting variables directly in the crontab for better control and performance.