Environment Variables

Before Starting

Consider these important facts:

• Environment variables are all upper case.
• To use their values, precede the name with a $.

Initializing Your Environment

When a bash session starts, it reads commands from ~/.bash_profile.

Environment variables are set in the file ~/.bashrc.

📝 Note: The files ~/.bash_profile and .bashrc are hidden. To list hidden files, type ls -a.

Know the Environment Variables

Here is a list of some common environment variables:

• $HOME - Path of your home directory
• $PATH - List of directories where the system checks for programs to run
• $LD_LIBRARY_PATH - List of directories where the system checks for shared libraries to load
• $HOSTNAME - The name of the host, e.g. or-slurm-login.

📝 Note: See the values of all your environment variables by typing env on your terminal.

Working with Environment Variables

• Display the value of an environment variable using echo:

  echo $HOME

• Modify the value of environment variables with export:

  export PATH=$PATH:/home/UID
  export LD_LIBRARY_PATH=$LD_LIBRARY_PATH:/home/UID/custom_lib_directory

• Set a value for environment variables:

  export OMP_NUM_THREADS=12

This command sets the value of the variable called OMP_NUM_THREADS (an OpenMP parameter) to 12.