Changing the login shell: chsh

    A user can change the default shell using the 'chsh' command,
    which stands for "change shell".  In doing this, the full path
    must be specified (e.g. /bin/tcsh or /bin/bash).

        - enter the command: chsh
        - when prompted, enter the user's password
        - enter the full path of the new shell: /bin/tcsh

    Note: on Mac OS X, it is good to use the -s options:

	chsh -s /bin/tcsh

-----------------------------------------------------------------

Setting the PATH under /bin/tcsh:

    The PATH variable controls the set of directories that are
    search for valid commands.

    There are 2 ways to update the PATH variable in the T-shell
    (or C-shell), either by updating the path shell variable, or
    by updating the PATH environment variable, directly.  This
    is because updating either path or PATH affects the other.  

    Adding ~/abin to the path may be done by:
	
	set path = ( $path ~/abin )
	

    Adding ~/abin to the PATH may be done by:
	
	setenv PATH {$PATH}:~/abin
	

    These commands have identical effect.  Either can be put
    into the ~/.cshrc file to affect the PATH every time a new
    shell is started (e.g. by opening a new terminal window).

    Note that under the newer Linux environments, the user will
    need to log out and log back in for this change to ~/.cshrc
    to fully take effect.

-----------------------------------------------------------------

Setting the PATH under /bin/bash

    The command to use for this shell is:
	
	export PATH=$PATH:~/abin
	

    This command may be put in the ~/.bashrc file, similar to
    the ~/.cshrc file, above.

-----------------------------------------------------------------

What does '~' mean?

    The shell interprets the '~' character as short-hand for the
    user's home directory.  To illustrate this, assume that some
    user's login name is pickle, and that on their machine, all
    users have home directories under /home.  Then for the user
    "pickle", any of the following 'cd' commands will change to
    their home directory (/home/pickle):
	
	cd
	cd ~
	cd /home/pickle
	cd ~pickle
	

    Note the last example.  The shell will interpret ~USER_NAME
    as shorthand for the home directory of user 'USER_NAME'.  So
    if there were a user named 'pizza' on the computer, then the
    following commands would change to pizza's home directory:
	
	cd /home/pizza
	cd ~pizza
	
    
    For another illustration, let us suppose that user 'pickle'
    has the directory 'abin' under their home (so the full path
    is /home/pickle/abin).  Then they could execute the command
    '3dDeconvolve' by entering either of the commands:
	
	~/abin/3dDeconvolve
	/home/pickle/abin/3dDeconvolve
	

    If somewhere in their ~/.cshrc file, they have the command:
	
	set path = ( $path ~/abin )
	

    then they would only need to use the shorthand command:
	
	3dDeconvolve
	

    because '3dDeconvolve' would be found (by the shell) under
    '/home/pickle/abin'.
-----------------------------------------------------------------