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# Environment Variables

Contents

- Environment Variables
  - Setting environment variables in Linux and OS-X
    - BASH/KSH
    - CSH/TCSH
  - Setting environment variables in windows

`HOME`

  The user’s home directory. On linux, `~` is shorthand for `HOME`.

`PATH`

  The list of directories searched to find executable programs

`PYTHONPATH`

  The list of directories that is added to Python’s standard search list when importing packages and modules

`MPLCONFIGDIR`

  This is the directory used to store user customizations to matplotlib, as well as some caches to improve performance. If `MPLCONFIGDIR` is not defined, `HOME/.config/matplotlib` is generally used on unix-like systems and `HOME/.matplotlib` is used on other platforms, if they are writable. Otherwise, the python standard library `tempfile.gettempdir()` is used to find a base directory in which the `matplotlib` subdirectory is created.

`MPLBACKEND`

  This optional variable can be set to choose the matplotlib backend. See What is a backend?.

## Setting environment variables in Linux and OS-X

To list the current value of `PYTHONPATH`, which may be empty, try:

    echo $PYTHONPATH

The procedure for setting environment variables in depends on what your default shell is. BASH seems to be the most common, but CSH is also common. You should be able to determine which by running at the command prompt:

    echo $SHELL

### BASH/KSH

To create a new environment variable:

    export PYTHONPATH=~/Python

To prepend to an existing environment variable:

    export PATH=~/bin:${PATH}

The search order may be important to you, do you want `~/bin` to be searched first or last? To append to an existing environment variable:

    export PATH=${PATH}:~/bin

To make your changes available in the future, add the commands to your `~/.bashrc` file.

### CSH/TCSH

To create a new environment variable:

    setenv PYTHONPATH ~/Python

To prepend to an existing environment variable:

    setenv PATH ~/bin:${PATH}

The search order may be important to you, do you want `~/bin` to be searched first or last? To append to an existing environment variable:

    setenv PATH ${PATH}:~/bin

To make your changes available in the future, add the commands to your `~/.cshrc` file.

## Setting environment variables in windows

Open the Control Panel (Start ‣ Control Panel), start the System program. Click the Advanced tab and select the Environment Variables button. You can edit or add to the User Variables.