A shell is the command line you use to enter commands for your computer to run. There are several different shells available for UNIX-like OSes which use different command syntaxes to carry out the same tasks.
Setting up your computer to run FSL may require you to know which shell you are running so that you can choose the correct set of commands to run or to choose which configuration file to edit.
We provide instructions for using the BASH and TCSH shells. In the vast majority of cases, if you don't know which shell you are using then it will most likely be BASH (as this is the default on Mac OS X and almost all Linuxes) but to confirm this, enter the following command into your terminal session:
echo $SHELL
If you see /bin/sh, /bin/bash or something similar you are using BASH (or a Bourne Shell equivalent). If you see /bin/csh, /bin/tcsh or something similar you are using CSH.