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Introduction to Basic Shell Commands

Objective:

This exercise will give you some more hands-on practice with the shell commands introduced in the previous reading. By the end of this exercise, you should be able to navigate your computer's file system, create, view, copy, and move files, and use wildcards.

1. Launch the Terminal

The terminal is where you'll enter shell commands. On most systems, you can find the Terminal application in the Applications menu or search for it. Note: on Windows, the newest terminal application is now called "Terminal" – yay! – which replaces the older PowerShell and even older Console. If you're on an older Windows machine, just substitute "PowerShell" or "Console" whenever we say "Terminal".

2. Navigating the File System

To navigate the file system, we need to be able to

  • see where we are – our current location in the file system
  • see what's there – which files and directories are housed in the current directory
  • jump around – change our current location to a new location in the file system

2.1. pwd – Print Working Directory

The pwd command lets us see where we are. It will display the path down the file tree from the very top, "root", all the way down to your current location. (Your current directory, without the whole path, might be displayed in your prompt or in the title bar of your terminal window.)

  • Type pwd and hit Enter (the "$" represents the terminal prompt, so don't type it).

    $ pwd
    • What's displayed? (Rhetorical question, but make sure you understand what you are seeing.)

    Don't be afraid to use this often! There's no crime in using it everytime you change you current location, just to be sure!

2.2. ls – List Files and Directories

The ls command will list files and directories (folders) in your current directory. By default, it will list everything that's not a "hidden" file in a short format, listing only the names.

  • Type ls and press Enter.

    $ ls
    • What do you see?

    The ls command has many options to filter what you see. Let's try some of them!

    • Try each of these in turn
    $ ls -l

    This lists the files and folders in "long" format, giving addtional information in each row. This will be useful later in your data science life but, now, not so much.

    $ ls -F

    This lists the files in Fabulous format (actually, it's probably classiFy – sometimes developers just pick a letter that's available and unlikely to be used for anything else...). This tells you what each thing is by appending a special character. Most usefully, it will put a backslash after directories.

    $ ls -a

    This lists all the files in the current directory, including hidden files whose names beging with a ".", which tells the OS to not show them to people by default. These are files that regular users don't need to worry about, and should only be messed with if you are sure you know what you're doing!

You can specify multiple options at once just by tacking them together. So, yes, you can do

$ ls -aF

Awesome aF, right?

2.3. cd – Change Directory

  • To navigate into a directory, use cd [directory_name]. If your want to jump into a directory that is in your current directory, you just type is name after cd. So, for example, if you have a "Documents" directory in your current folder, you can jump into it with:

    $ cd Documents

    Do another ls -F, pick a directory, and jump into it.

    • You can go back to the "parent" directory (the one that contains the current directory) using: 
      $ cd ..
      Where ever you may roam, you can jump instantly back to your home directory using 
      $ cd ~
      So "~" always means your home directory, ".." always means the parent directory. "." means the current directory, but you won't need that much.

3. Manipulating Files

3.1. touch – Create a New File

  • Type touch my_file.txt and hit Enter. 
    $ touch my_file.txt

You just made a new file! (Use ls to confirm!). Why "touch"? If you use it on an existing file, it updates the modification date (so you didn't edit it, but you touched/poked/hugged it to let it know you care). You'll almost always use it to create a new file though.

3.2. cp – Copy a File

  • Copy my_file.txt to a new file named my_copy.txt:

    $ cp my_file.txt my_copy.txt
    • Use ls to see both files.

3.3. mkdir – Make a new directory

  • Make a new directory named "TestDir" in the current folder.

    $ mkdir TestDir
    • Use ls -F to see your new directory with a "/" after it.

See if you can figure out how to put a copy (cp) of "my_file.txt" into your new directory, "TestDir". Hint, you can specify a file using a file path from your current directory. So Documents/my_copy.txt would specify the file "my_copy.txt" in the directory "Documents" in your current directory.

For all the following examples, feel free to use ls often to confirm that what you did worked!

3.4. mv – Move or Rename a File

  • Move my_file.txt to your TestDir directory:

    $ mv my_file.txt TestDir/my_file.txt

  • You can use mv if you just want to rename a file. You're effectively "moving" the file contents into a file with the new name:

    $ cd TestDir
$ mv my_file.txt my_renamed_file.txt

    Pop back up into the parent directory (should be your home directory). Now see if you can rename a file in TestDir without changing directories.

4. Wildcards

4.1. Using * Wildcard

  • The * wildcard matches any number of characters. Just like if "Aces are wild" in a card game, the ace can serve as any card in the deck for your hand, the splat, *, will match anything. Let's see how this is useful.

  • Create a few more files in TestDir for this example:

    $ cd TestDir
$ touch file1.txt file2.txt file3.doc

  • Now, using the wildcard, we can list just the text files (.txt extension):

    $ ls *.txt

  • or only the files with "file" in the name:

    $ ls *file*

The wild card is very useful; make it your friend!

5. Clean Up

  • Let's clean up the files we created. We can do this using the rm command to remove stuff. Be Carefull! This command asks you no questions and tells you no lies. If you rm a file, it's gone forever. It does not go into a "Trash" folder from which you can grab it back.

  • We could remove the files one-by-one. Let's remove 2 like this:

    $ rm file1.txt file2.txt

    Or we could just remove the whole directory we made.

    $ cd ..
$ rm -r TestDir

    The -r option stands for "recursive"; it means delete the directory and all its contents.

    Make a new directory, put a new file it it, and try to use just rm to delete it with no -r option.

    So rm is unforgiving, but it's not downright mean. Go ahead and clean up with rm -r.

Conclusion:

Well done! You've now taken your first steps into the world of shell commands. With practice, these commands will become second nature to you. Remember, the terminal is a powerful tool, and the commands you've learned today are just the tip of the iceberg!

Do yourself a favor. Keep your terminal muscles toned by using the terminal a lot, even when you don't need to. For example, whenever you're working on a project in some folder on your computer, even writing a paper, open a terminal in that folder and see what all is in there. Use it to copy or remame files instead of using the "Save As..." menu from within the application.