Creating and Changing Folders
=============================

On a Windows or Mac desktop, our present location determines what files and folders
we can access. I can "see" my present location visually with the help of the graphic
interface - I could be looking at my Desktop, or the contents of a folder, for example.
In a Linux command-line interface, we lack the same visual queues to tell us what our
location is. Instead, we use a command - ``pwd`` (print working directory) - to tell
us our present location. Try executing this command on Lonestar6:

.. code-block:: console

   $ pwd
   /home1/03439/wallen

This home location on the Linux filesystem is unique for each user, and it is roughly
analogous to C:\\Users\\username on Windows, or /Users/username on Mac.

To see what files and folders are available at this location, use the ``ls`` (list) command:

.. code-block:: console

   $ ls

I have no files or folders in my home directory yet, so I do not get a response.
We can create some folders using the ``mkdir`` (make directory) command. The words 
'folder' and 'directory' are interchangeable:

.. code-block:: console

   $ mkdir folder1
   $ mkdir folder2
   $ mkdir folder3

.. code-block:: console

   $ ls
   folder1 folder2 folder3

Now we have some folders to work with. To "open" a folder, navigate into that folder 
using the ``cd`` (change directory) command. This process is analogous to double-clicking 
a folder on Windows or Mac:

.. code-block:: console

   $ pwd
   /home/03439/wallen/
   $ cd folder1
   $ pwd
   /home1/03439/wallen/folder1

Now that we are inside ``folder1``, make a few sub-folders:

.. code-block:: console

   $ mkdir subfolderA
   $ mkdir subfolderB
   $ mkdir subfolderC
   $ ls
   subfolderA subfolderB subfolderC

Use ``cd`` to Navigate into ``subfolderA``, then use ``ls`` to list the contents. What do you expect to see?

.. code-block:: console

   $ cd subfolderA
   $ pwd  
   /home/03439/wallen/folder1/subfolderA
   $ ls

There is nothing there because we have not made anything yet. Next, we will navigate back to the 
home directory. So far we have seen how to navigate "down" into folders, but how do we navigate 
back "up" to the parent folder? There are different ways to do it. For example, we could specify 
the complete path of where we want to go:

.. code-block:: console

   $ pwd
   /home1/03439/wallen/folder1/subfolderA
   $ cd /home1/03439/wallen/folder1
   $ pwd
   /home1/03439/wallen/folder1/

Or, we could use a shortcut, ``..``, which refers to the **parent folder** - one level higher 
than the present location:

.. code-block:: console

   $ pwd
   /home1/03439/wallen/folder1
   $ cd ..
   $ pwd
   /home1/03439/wallen

We are back in our home directory. Finally, use the  ``rmdir`` (remove directory) command to remove 
folders. This will not work on folders that have any contents (more on this later):

.. code-block:: console

   $ mkdir junkfolder
   $ ls
   folder1 folder2 folder3 junkfolder
   $ rmdir junkfolder
   $ ls
   folder1 folder2 folder3

A bonus command available on some Linux operating systems is called ``tree``. The ``tree`` command 
displays files and folders in a hierarchical view. Use another Linux shortcut, ``.``, to indicate 
that you want to list files and folders in your **present location**.

.. code-block:: console

   $ tree .
   .
   |-- folder1
   |   |-- subfolderA
   |   |-- subfolderB
   |   `-- subfolderC
   |-- folder2
   `-- folder3

Before we move on, let's remove the directories we have made, using ``rm -r`` to remove our parent 
folder ``folder1`` and its subfolders. The ``-r`` command line option recursively removes subfolders 
and files located "down" the parent directory. ``-r`` is required for non-empty folders.

.. code-block:: console

   $ rm -r folder1
   $ ls 
   folder2 folder3

Which command should we use to remove ``folder2`` and ``folder3``?

.. code-block:: console

   $ rmdir folder2
   $ rmdir folder3
   $ ls

Why could we use ``rmdir`` on ``folder2`` and ``folder3``, but not on ``folder1``?


Review of Topics Covered
^^^^^^^^^^^^^^^^^^^^^^^^

+------------------------------------+-------------------------------------------------+
| Command                            |          Effect                                 |
+====================================+=================================================+
| ``pwd``                            |  print working directory                        |
+------------------------------------+-------------------------------------------------+
| ``ls``                             |  list files and directories                     |
+------------------------------------+-------------------------------------------------+
| ``ls -l``                          |  list files in column format                    |                                                 
+------------------------------------+-------------------------------------------------+
| ``mkdir dir_name/``                |  make a new directory                           |
+------------------------------------+-------------------------------------------------+
| ``cd dir_name/``                   |  navigate into a directory                      |
+------------------------------------+-------------------------------------------------+
| ``rmdir dir_name/``                |  remove an empty directory                      |
+------------------------------------+-------------------------------------------------+
| ``rm -r dir_name/``                |  remove a directory and its contents            |
+------------------------------------+-------------------------------------------------+
| ``tree``                           |  list files and directories hierarchically      |
+------------------------------------+-------------------------------------------------+
| ``.`` or ``./``                    |  refers to the present location                 |
+------------------------------------+-------------------------------------------------+
| ``..`` or ``../``                  |  refers to the parent directory                 |
+------------------------------------+-------------------------------------------------+