At times I’d just like to run a script or a program without using my current or pre-existing shell environment variables. Running bash -l doesn’t really help because it just starts a new bash shell login with the same environment variables from your ~/.bashrc or profile.d system-wide settings. Well, the other day I discovered prefixing your program/script with env temporarily clears your environment variables so that your script just runs with totally no variables!

Displaying Current Environment Variables

From the terminal, env or printenv will show you your current environment variables. For example:

$ env
XDG_VTNR=2
CUDA_INC_PATH=/usr/include/cuda
XDG_SESSION_ID=4
HOSTNAME=vast
PYENV_ROOT=/home/james/.pyenv
ANDROID_HOME=/home/james/src/android-sdk-linux
XDG_MENU_PREFIX=gnome-
SHELL=/bin/bash

Temporarily Clearing Bash Environment Variables

Now, to run a program/script without any environment variable(s), prefix your command with env -i.

• The syntax is as follows:

  $ env -i /path/to/your/program arg1 arg2 ...
  

• For example:

  $ env -i ls -l
  

The -i option tells env command to completely ignore the environment

To set an environment variable, just initialize the variable with a value immediately after the env command.

• The syntax is as follows:

  env var=value /path/to/your/program arg1 arg2 ...
  

• For example:

  $ env CUDA_INC_PATH=/tmp/src/cuda /usr/bin/nvidia-smi