# Set environment variables¶

## CLAW¶

To use the Fortran versions of Clawpack you will need to set the environment variable CLAW to point to the top level of clawpack tree (there is no need to perform this step if you will only use PyClaw). In the bash shell these can be set via:

export CLAW=/full/path/to/top/level


## FC¶

You also need to set FC to point to the desired Fortran compiler, e.g.:

export FC=gfortran   # or other preferred Fortran compiler


Consider putting the two commands above in a file that is executed every time you open a new shell or terminal window. On Linux machines with the bash shell this is generally the file .bashrc in your home directory. On a Mac it may be called .bash_profile.

If your environment variable CLAW is properly set, the command

ls $CLAW  should list the top level directory, and report for example: README.md riemann/ pyclaw/ amrclaw/ setup.py clawutil/ geoclaw/ visclaw/ classic/  ## PYTHONPATH¶ If you installed from a tarfile or using a git clone without using pip, then you will need to set the PYTHONPATH variable in order for the Python codes to be found. This is not necessary if you used pip to install (see Installation instructions (pip)). See Python path for more about Python paths and this environment variable. In the bash shell, for example, this path can be set via: export PYTHONPATH=/path/to/clawpack:$PYTHONPATH


Note that this places this new path at the front of any existing path, and will be searched before other directories where you might have a different version of Clawpack, e.g. if you have used pip to install a different version and there is a path in a site-packages/easy-install.pth file.

Using PYTHONPATH can also be useful if you want to use different versions of Clawpack in different shells, e.g. when dual-debugging or for different projects.