2 Lesson 02

2.1 Command Line

The knowledge of “command line” opens a whole new world of opportunities, as the number of interface-less programs and applications is significantly larger; command line also offers a more robust and direct controls over a computer. The main goal is to learn the basics of this indispensable tool.

We can use Terminal on Mac (installed), Powershell on MS Windows (should be installed), although other command line tools will work as well.

Before we proceed, however, let’s discuss a few concepts:

  • What a filesystem is
  • How to run a program from the command line
  • What it means to run a program
  • How the computer knows what program to run
  • How to refer to a file from the command line

2.1.1 The filesystem

Every disk contains a filesystem and information about where disk data is stored and how it may be accessed by a user or application. A filesystem typically manages operations, such as storage management, file naming, directories/folders, metadata, access rules and privileges. Commonly used file systems include File Allocation Table 32 (FAT 32), New Technology File System (NTFS) and Hierarchical File System (HFS).

All the files and programs on your computer are organized into folders; all these folders are in some other folders all the way down to your hard drive, which we call the root of your filesystem. Every hard drive, USB drive, DVD, and CD-ROM has its own filesystem.

You normally look at the contents of your filesystem via the Finder (on Mac) or the Explorer (on Windows). Open a window there now.

The Finder / Explorer window opens in some folder, which might be different depending on what computer operating system you’re using. But you’ll usually have a navigation bar to the left, that will let you go to different places. You see folders, also known as directories, and you might see files too.

One thing that computer OSes like to hide from you is the fact that you have a home directory, where all your personal files and folders should live. This makes it easier for multiple users to use a single computer. You can find your home directory like this:

  • On Mac, select Go > Home in the menu.

  • On Windows, click on Local Drive (C:), then click on Users, then click on your login name.

You’ll see that your home directory has several folders in it already, that were created automatically for you when you first made a user account.

Now how can you tell where you are, with respect to the root of your drive?

  • On Mac, select View > Show Path Bar in the menu.

On Windows, look:

The Finder / Explorer will also show you where in your computer’s filesystem you are. This is called the path—it shows you the path you have to take from the root of your filesystem to the folder you are in.

Now if you are on Windows, click on that bar and you’ll see something surprising.

This is your real path. The C:\ is how Windows refers to the root of your filesystem. Also note that, even if your OS is not in English, the path may very well be!

2.1.2 Getting started with the command line

Now that you have a hint of what is going on behind the scenes on your computer, let’s dive into the command line. Here is how you get there:

  • On Mac, look for a program called Terminal.app

  • On Windows, look for a program called Powershell

By default, these shells open in your home directory. On Windows this is easy to see, but on Mac it is less clear—that is, until you know that this ~ thing is an alias for your home directory.

2.1.3 Components of the command line

The command line consists of a prompt where you type your commands, the commands and arguments that you type, and the output that results from those commands.

The prompt is the thing that looks like (where user is your username):

MacBook-Pro:~ user$

or

PS C:\Users\user>

You will never need to type the prompt. That means that, if you are noting down what we do in class for future reference, you should not copy this part!

The prompt actually gives you a little bit of information.

  • On Mac, it has the name of the computer, followed by a :, followed by the directory where you are, followed by your username, with $ at the end.
  • On Windows, it has PS for PowerShell, followed by the name of the drive (C for most of you), followed by a :, followed by the full path to where you are, with > at the end.

When you type a command, nothing happens until you press the Return/Enter key. Some commands have output (more text that appears after you press Return/Enter) and others don’t. You cannot run another command until the prompt is given again.

NOTE: From this point on, you will be running the commands that are run here!

Let’s first make sure we are in our home directory by typing cd ~. For most of you this should change nothing, but now you know your first shell command. The cd stands for change directory, and what follows is the directory you want to go to.

cd ~

Now let’s have a look around. The command to show what is in any particular directory is called ls, which stands for list. Try running it.

ls

If you are on Windows, what you get will look more like this:

PS C:\Users\user> ls

You should then see something like:

Verzeichnis: C:\Users\user


Mode                LastWriteTime     Length Name
----                -------------     ------ ----
d----        23.02.2016     21:18            .oracle_jre_usage
d-r--        23.02.2016     20:40            Contacts
d-r--        23.02.2016     20:40            Desktop
d-r--        23.02.2016     21:11            Documents
d-r--        23.02.2016     21:16            Downloads
d----        23.02.2016     21:24            exist
d-r--        23.02.2016     20:40            Favorites
d-r--        23.02.2016     20:40            Links
d-r--        23.02.2016     20:40            Music
d-r--        23.02.2016     20:40            Pictures
d-r--        23.02.2016     20:40            Saved Games
d-r--        23.02.2016     20:40            Searches
d-r--        23.02.2016     20:40            Videos


PS C:\Users\user>

Now go into your documents folder and look around.

cd Documents
ls

How does this compare to what you see in the Finder / Explorer window, if you click on the Documents folder?

Another important command, which tells you where you are at any given time, is pwd. This means print working directory. Try it now and see what you get.

pwd

If ever you get lost on the command line, pwd will always help you find your way.

2.1.4 File paths and path notations

By now you will have noticed that I’ve mentioned the path a few times, and that it seems to have something to do with this thing that pwd prints out. (And, most annoyingly, that it looks different on Mac and Windows) The bit of text that you get from pwd is what is called path notation, and it is very important that you learn it if you want to do anything with your own digital data. Here are some rules:

  • The / (or \\ on Windows) separates folder names. So Desktop/Video means “the thing called Video inside the Desktop folder”.
  • The / all by itself refers to the base of your hard drive (usually Macintosh HD or C:\.)
  • The ~ refers to your home folder.
  • These things can be combined; ~/Documents means “the Documents folder in my home folder.”
  • The . means “the current working directory”, i.e. what you would get if you ran the command pwd.
  • The .. means “one directory back”—if pwd gives you /Users/user, then .. means /Users.
  • If the path does not start with a . or a / or a ~, then it will be assumed to start with a ./, that is, “start from the current working directory.”

Let’s wander around a bit. But, first, let’s download a zip file with somoe materials for this class. Unzip it somewhere and go to that folder in your Terminal or Powershell.

cd /path/to/the/folder/tnt_practice_materials
pwd
cd ./cd 02_CommandLine/
pwd
ls

Try the following if you are on Mac

ls -lh
cd ..
pwd

NB: you can use TAB to autocomplete the path: type ls to see what folders are in Documents, then go to any one of them by typing cd (space) and then the first two letters > after that use TAB and the name will be complete automatically.

cd 03[TAB]
pwd
cd ../01[TAB]
pwd
ls McCarty_Modeling.pdf
cd ..

2.1.5 Command line arguments

So far we have learned three commands: cd, ls, and pwd. These are useful for navigation, but we can run a lot more commands once we learn them, and have a need for them!

What are we doing, exactly?

  • First word is the command
  • All other words are the arguments
  • Words must be separated by spaces

cd is a command that expects an argument: the name of the directory you want to go to. But what if the name has a space in it?

NB: You may think of most commands as sentences with subject, predicate, and object (or multiple objects).

cd ./01_Zotero_Word/Green Eggs and Ham

What happened there?

Well, we have a folder called Green Eggs and Ham in our example, and we tried to go there. But since the command line works with arguments, and since arguments are separated by space, the machine interpreted this as if we were saying “Change to the ./01_Zotero_Word/Green folder, and then Eggs, and, Ham, whatever that means.” And it gave us an error, because we don’t have a folder called Green in our example.

You can get around this. How you get around it depends on whether you’re on Windows or not. One way to get around it that should work both places is like this:

On Windows:

cd './01_Zotero_Word/Green Eggs and Ham'

On Mac (you need to escape spaces by adding a backslash in front of them):

cd ./01_Zotero_Word/Green\ Eggs\ and\ Ham/

NB: The easiest solution is to use TAB for autocomplete!

2.1.6 More commands

With command line you can do everything that you became accustomed to be doing in a graphical interface of your favorite file manager. For example, you can copy, move, and delete files and folders.

You can use:

  • mv to move files
  • rm (on Windows also: del) to remove/delete files
  • cp to copy files

In all cases you need to state which files you want to mv, rm, or cp. In some cases you also need to point where you want to mv or cp your files.

NB: Syntax on Mac and Windows will vary slightly, but if you keep using [TAB] for autocompletion, there will be no different in the process of typing the command, so let’s try to do it this way.

To start, let’s go to the root directory of our course materials. From there, let’s do the following:

cd 01[TAB]
ls
cp Mc[TAB] Green[TAB]
cd Green[TAB]
ls

NB: when you hit [TAB] after Mc you are not going to get the full autocomplete, because there are two files that start with McCarty_Modeling—one is pdf and another—txt. You will need to type one more letter p and then hit [TAB] again to get the file name that you need. Thus, the command can be transcribed as: M[TAB]p[TAB]

Now let’s rm (delete) the McCarty_Modeling.pdf from this folder, then go to the folder where we copied it, and then mv (move) it back to where it was in the first place.

rm M[TAB]p[TAB]
ls
cd G[TAB]
mv Mc[TAB] ../
cd ..
ls

Tada! The McCarty_Modeling.pdf should now be back where it was.

If you want to learn about new commands, try to google. Googling things like this is a very big part of being a DH scholar! You will most likely find your answers on https://stackoverflow.com/, which will become your most frequented resource, if you embark on the DH path.

2.2 Homework

Command line

Python

  • Work through Chapter I of Zelle’s book; read the entire chapter; retype and run all code snippets as described in the book; work through the chapter summary and exercises; complete all programming exercises;
    • For submission: email me the results of “Programming Exercises”. In your submission there should be text files or python script files for exercises 1 (results of print function), 3, 4, 5, 7. Each python script should be working, i.e. you should be able to run it and get relevant results. You are welcome to discuss any of these assignments on Slack.
  • Work through the following videos from Dr. Vierthaler’s Hacking the Humanities series:

Submitting homework:

  • Homework assignment must be submitted by the beginning of the next class;
  • Email your homework to the instructor as attachments.
    • In the subject of your email, please, add the following: CCXXXXX-LXX-HW-YourLastName-YourMatriculationNumber, where CCXXXXX is the numeric code of the course; LXX is the lesson for which the homework is being submitted; YourLastName is your last name, and YourMatriculationNumber is your matriculation number.