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Command Line Interface

Project Time

About 1 hour

  • 25 minutes for video walkthrough of slides
  • 20 minutes for Independent Practice
  • 20 minutes for Check for Understanding

Prerequisites

none

Motivation

  • It is a more efficient way of accessing the computer's capabilities.
  • Many software libraries and tools can only be downloaded via the Command Line (such as Node Package Manager (npm)).
  • Error messages will often print out to the Command Line.

Which companies use the Command Line? Every company will expect you to be able to navigate the Command Line.

Looking at an example website

  • Sometimes you will see instructions on a website, and there will be a dollar sign followed by text, like so:
$ cd Downloads/
  • Go to www.npmjs.com/package/express, which is the Node Package Manager page for Express.js.
  • Everything in the block after the "$" is the command that you would type into the Command Line in order to install Express.js.

Objectives

Participants will be able to:

  • Create a directory and files
  • Navigate to a directory
  • Change the name of the file
  • Copy a file to a directory

Lesson

First, spend 5 minutes setting up bash in your terminal by following these directions. Some of the common commands we are about to use require bash, but the Catalina operating system on Mac uses a zsh shell by default.

Video walkthrough of lesson slides: Command Line Interface

  • Please watch the video the first time without working along with the demonstration. Just absorb the concepts. Then, you can watch the demonstration a second time and code with the instructor if you like.

Read through lesson slides: Command Line Interface

Accessing the Command Line ("Terminal")

  1. Hold down the COMMAND key and press the spacebar once. This opens the OSX launcher, Spotlight.
  2. When the search bar appears type "terminal" and press ENTER to launch the Terminal app.
  3. The Terminal appears as a new window on the desktop and an icon in the dock.

List of basic Terminal commands

man - read a manual page
apropos - find what man page is appropriate
pwd - print working directory
cd - change directory
echo - print some arguments
ls - list directory
find - find files
mkdir - make directory
cd - change directory
rmdir -remove directory
pushd - push directory
popd - pop directory
cp - copy a file or directory
mv - move or rename a file or directory
hostname - my computer’s network name
less - page through
more - page through (alternate)
history - see previous commands from this shell
head - print the start
tail - print the end
mkdir - make directory
rmdir - remove directory
grep - find things inside files
cat - print the whole file
man - read a manual page for a program
env - look at your environment
export - export/set a new environment variable
which - see path to a program
exit - exit the shell
sudo - become the super user, root (DANGER - only use when necessary)
chmod - change permission modifiers
chown -  change ownership

Demonstration

Instructor demonstrates how to use many of the above commands in the video walkthrough of the lesson slides.

Common Mistakes / Misconceptions

  • "I have always just downloaded everything I need with my mouse. I don't need to use the CLI." As you continue programming, you will learn new languages and tools. There are some important tools out there that can only be accessed via CLI. One example is NPM (node package manager), which we'll use in a few weeks.

  • "I am afraid of getting into the wrong directory. Isn't it easier to just click and type? " There are simple commands you can run in the CLI to check which directory you're in. Once you get into the habit of using the CLI, you can quickly navigate through files and directories without leaving the keyboard, greatly increasing speed and efficiency.

  • "What if I accidentally delete important directories or files that affect my computer's operations? " Most files and directories for computer operation are protected in some way. They could be hidden or have higher permission settings. Hidden files, for example, have a dot in front of their file name, and you can't see them without certain commands or special settings. If you are editing such files and you don't know why, please check with the instructor.

A note about naming files and folders

helloThisIsCamelCase becauseCamelsHaveHumps
this_is_snake_case there_are_snake_friends_between_words
this-is-kebab-case it-looks-like-the-words-are-stuck-on-kebabs

We use camelCase in JavaScript! We tend to use snake_case.html for filenames on Unix & Linux systems. We tend to use kebab-case for directory (folder) names and git repository names.

Independent Practice

  1. Navigate to your Desktop. Create a directory named "foo". Use cd foo to navigate into "foo" and create another directory named "bar".

  2. Run cd bar. What directory are you in now? Check by running pwd.

  3. Run cd ../. What directory do you think you are in now? Check by running pwd.

  4. Navigate back to the "bar" directory and run touch first.txt and touch ../second.txt. You have not cd'd into the "foo" directory, but your second command contained ../. Can you guess where second.txt is located?

  5. Check your answer by running ls inside both the "foo" and the "bar" directory. The second.txt file should be inside the "foo" directory.

  6. Navigate into the "bar" directory. Run cp first.txt ../. Use ls and make sure both directories have a first.txt file.

  7. Navigate back into the "foo" directory. Run mv second.txt foofile.txt, then run ls. What happened to "second.txt"?

  8. Use TAB key to autocomplete the names of directories and files while in the command line faster as it'll autocomplete the string as far as it can before you have to disambiguate. Hit the tab twice to see the list of autocomplete possibilities (if multiple matches).

  9. The root directory is the directory that contains all other directories and files on the system and which is designated by a forward slash ( / ). Root is the very top directory of the directory tree diagram. The root directory of a GitHub project is the top most directory of your git project which contains all the files hosted on GitHub.

  10. You can immediately open whatever folder or directory you are working within into the Finder of MacOS and Mac OS X by simply typing open . and executing it
    open is not magically connected to Mac's Finder, but actually it's just using whatever default program on your Mac opens a file with that extension, and in the case of directories, the default program is Finder.

  11. Another Mac shortcut cmd+ shift+ g can be used anywhere you see a Finder window (even in other Mac programs such as SourceTree or VSCode when you're opening a file or directory). This brings up a little text box into which you can type or paste a path. Use pwd to get your current path, then copy it from the terminal and open up SourceTree, go to file > open, then use cmd + shift + g to paste in the path you want.

  12. ls command is used to peek into other folders. The list of ls arguments are ls -l : shows file or directory, size, modified date and time, file or folder name and owner of file and its permission. ls -a : lists all the files including hidden files. ls -lh: shows sizes in human readable format.

cd commands

  1. To navigate to your home directory, use "cd" or cd ~
  2. To navigate up one directory level, use cd ..
  3. To navigate to the previous directory (or back), use cd -
  4. To navigate into the root directory, use cd /
  5. To navigate through multiple levels of directory at once, specify the full directory path that you want to go to. For example, use cd ~/OFGT-data/images to go directly to the images subdirectory in the OFGT-data folder. As another example, cd ~/Desktop will move you to the Desktop subdirectory inside your home directory.

Absolute Path vs Relative Path

absolute path

  1. Start at the root directory ( / ) and work down.
  2. Write a slash ( / ) after every directory name (last one is optional) For Example: cat /home/kt/abc.sql

relative path

  1. Relative path is defined as the path related to the present working directly(pwd).
  2. It starts at your current directory and never starts with a ( / ). For Example: $pwd /home/kt $cd abc

Challenge

Run the ls -l command in the "foo" directory and compare it to the outcome of just running the ls command. The output from ls -l is different -- how?

Next, run man ls. Scroll to the bolded title "The Long Format". The first few paragraphs talk about what -l displays. Look for the one that starts with "The file mode...". Read it and see if your guess is correct.

Scroll through the manual and see if you can get an idea of what the format of a manual is typically like. Feel free to check out the manual for some of the command above. Whenever you are done, type q to exit.

Click here to learn more advanced commands.

Check for Understanding

  • Why is Command Line Interface used?
  • Mention some Terminal Commands along with their use.
  • Which key is used to autocomplete the names of directories and files?
  • What is a root directory?
  • Differentiate between Absolute and Relative path.

Supplemental Materials