1 - Dev Tools and command line

Table of Content

Operating Systems

An Operating System (OS) is a powerful, and usually large, program that controls and manages the hardware and software on a computer. All computers and computer-like devices require operating systems, including laptops, tablets, desktops, and smartphones. The OS performs all the basic tasks like file management, memory management, process management, handling input and output, and controlling peripheral devices such as disk drives and printers.

The most common operating systems for desktop and laptop computers are:

Microsoft Windows (Windows 95, Windows 7, Windows 10,...)
Linux (Debian, Red Hat, Ubuntu,..)
MacOS
Chrome OS
Android and iOS are operating systems for mobile devices.

Unix

Unix is a family of operating systems. The first version was developed starting in 1969. Unix is characterized by being portable and multitasking.

Unix operating systems are widely used in a multitude of devices that range from the most capable supercomputers to the mobile phones and computers that we use daily. The philosophy of Unix systems is characterized by:

a hierarchical file system,
a large collection of small programs that can work in series,
the use of text files to store the data,
treating devices as files.

Linux and MacOS are examples of Unix systems.

Linux

Linux is a family of Unix-like operating systems that use the Linux kernel. The name comes from the original programmer, a student named Linus Torvals, who in 1991, working with the GNU project of the Free Software Foundation, created the first version of this operating system.

Linux development is one of the clearest examples of free, open source software development by a diverse community of programmers all over the world. Anyone can use the operating system, study it and modify it. The open source nature of Linux is protected by the GPL (GNU General Public License).

Ubuntu

Ubuntu is a Linux distribution. It is an open-source operating system aimed at desktop users, and its strengths are that it is easy to use and install. Although the desktop is somewhat different from Windows or Mac OS, a user who is accustomed to any of these operating systems will not have many problems becoming familiar with Ubuntu. Ubuntu is a Linux distribution based on Debian and composed mostly of free and open-source software. Ubuntu is officially released in three editions: Desktop, Server, and Core for Internet of things devices and robots.

If you are using Ubuntu, you will see this sreen:

Demo of Ubuntu:

The friendly Desktop
The filesystem: navigate through folders and files using File Manager
Ubuntu software: a tool to install software easily

The Command Line

The Command Line, also knows as Bash, Terminal or Shell (Línea de Comandos ó Símbolo de sistema in Spanish) is a way of controlling a computer, based on a text interface.

Why should I use the command line/terminal?

Once you know the basics, it helps you to interact with you computer faster
Some software for developers must always be used from a terminal
You have more control over the software
It allows you to create scripts (lists of commands) and automate manual tasks
It is what hackers use in movies.

How do I use the terminal on my computer?

Here are the instructions for the three operating system:

MacOS: You can find the Terminal.app in your Applications, in the folder Utilities. An alternative way to open the Terminal is to search with Spotlight and type in “terminal”. Select the application called terminal and press the return key. This should open up an app with a black background. When you see your username followed by a dollar sign, you’re ready to start using the command line.
Linux: You can open the Terminal by directly pressing [ctrl+alt+T] or you can search for it by clicking the dash (#) icon, typing in “terminal” in the search box, and opening the Terminal application. This should open up an app with a black background. When you see your username followed by a dollar sign, you’re ready to start using the command line.
Windows: Windows has its own Command Prompt. It is very similar to the Unix command line, but some commands are not exactly the same. For the main differences go to this link. Because of these differences, and because we want to learn UNIX commands, we use the Git Bash. Go to the Windows "Start" button and search the program Git Bash. When you open it you will see a screen like this one:

After you have followed the instructions, open a terminal and write ls, then press the Enter key. What do you see?

Commonly used commands

These are the most used commands that you will quickly become comfortable with during the course. These commands allow you to effectively move around the filesystem and write software on your laptop. There are more commands in the tables with more commands and descriptions below.

cd - change directory. To move up one folder level and into the parent directory use: cd ..
ls - list the contents of a directory. Can also be used as ls [directory_name] to list the contents of a specific directory without actually moving (with cd) to it
pwd - print working directory: print the full location of the folder you are working in
mkdir [name] - make directory: create a new directory, with the given name after a space
touch [file_name] - create a new file, with the given name (don't forget to add the extension, like .css or .html)
rm [file_name] - remove a file
rm -r [directory_name] - remove a directory (and all files inside that directory)

Getting Help

When you're stuck and need help with a command, help is usually only a few keystrokes away. Help on most commands is built right into the commands themselves, available through online help programs (such as https://linux.die.net/man), and of course online.

Using a command's built-in help Many (but not all) commands have simple help screens that can be called with special command flags. These flags usually look like -h or --help. Example: grep --help.

Online manuals: the man pages The best source of information for most commands are the manual pages, also known as the man pages. To read a command's man page, type man plus a space and the command.

Example

Info

man ls

Get help on the ls command

man man

Get the manual for info on the manual!

Beginner Level

{ Navigating in Terminal. }

Objectives:

By the end of this chapter, you should be able to:

Define what Terminal is and how it is structured
Navigate through and list files on your machine
Define the following terms: shell, terminal, directory, absolute path, relative path

Linux/Mac

Windows

Description

pwd

cd

print working directory: shows current location

cd

cd, chdir

change directory; returns to the home directory

cd directory

change into the specified directory

cd ~

~ means home directory; shortcut to the home directory

cd ..

move up one directory

cd -

returns to the directory of your previous location

ls

dir /w

list all files in current directory

ls directory

dir directory

list all files in the specified directory

ls -l

dir

list all files in long format: one file per line, with info about the file

ls -a

dir /a

list all files, including hidden files (= filenames that start with .)

ls -ld directory

show detailed information about the directory

ls /usr/bin/d*

dir d*.*

list all files starting with d in the /usr/bin directory

What is Terminal?

Terminal is an application that gives us a command line interface (or CLI) to interact with the computer. Everything you can do in Finder/Windows Explorer you can do in Terminal. Developers use Terminal because it is usually much faster to use Terminal than a graphical user interface (GUI) such as Finder/Windows Explorer. Although the Terminal interface can seem daunting at first, with a bit of practice, you'll be up to speed in no time!

What is a shell? Bash/ZSH

You will also hear the term "shell" when learning about Terminal so it is important to distinguish between these terms. From Stack Overflow:

The shell is the program which actually processes commands and returns output. Most shells also manage foreground and background processes, command history and command line editing. These features (and many more) are standard in bash, the most common shell in modern linux systems. (We are using zsh).
A terminal refers to a wrapper program which runs a shell. Decades ago, this was a physical device consisting of little more than a monitor and keyboard. As unix/linux systems added better multiprocessing and windowing systems, this terminal concept was abstracted into software.

If you are using Windows, there is a great tool called Babun, which is a shell that you can install and use the same commands as if you were on Mac or Linux. This is not essential, but using it will enable you to more easily follow along with the material.

How Terminal is Structured

In Terminal, all files and folders begin at the root directory. The root directory is noted by a /. Inside the root directory are essential files/folders that your machine needs, but we do not modify the files and folders in the root directory often. Inside of the root directory, we have a folder called Users which contains all of the user accounts on your computer. If you move into the directory for your user account, you will be in the home directory, which is denoted by ~. For example, if your user name on the computer is eschoppik, then your home directory would be /Users/eschoppik. A synonym for the /Users/eschoppik path is ~ when you are logged in as eschoppik.

Moving Around

The first thing you want to start to understand when using Terminal is how to navigate from folder to folder. One of the most common commands you will be using in Terminal is cd which is short for "change directory." In order to change a directory, type cd followed by the directory or a path to the directory. If we want to move up a directory we use cd .. and if we want to move into a directory we specify the name of the directory we are moving into. For example, if you are in your home directory and type cd Desktop, you should move into your Desktop directory.

We just mentioned that you can type cd followed by a directory or path. But what is a path? Let's learn some more vocabulary:

Absolute Paths vs Relative Paths

A path is simply the way to reach a file or folder; it's like an address for the file or folder you're trying to reach. When we specify a path starting from the root directory /, we call that an absolute path. For example, if I am currently in the ~ home directory and I would like to change directories into my Desktop folder, I can do that in two of the following ways:

cd Desktop - relative to where I am currently
cd /Users/eschoppik/Desktop - absolute, starting from the root (first /, then Users, then eschoppik, then Desktop)

Questions to Answer

What is the difference between / and ~? What do we call each of these directories?
What command do we use to change directories?
What is the difference between an absolute and relative path?

{ Working with Files and Folders. }

Objectives

By the end of this chapter, you should be able to:

Create files and folders in Terminal using mkdir and touch
Move files and folders in Terminal using mv
Copy files and folders in Terminal using cp
Remove files and folders in Terminal using rm and rmdir
Explain what a flag is in Terminal
Explain what the following commands do: whoami, pwd, cat, echo, less, open

Linux/Mac

Windows

Description

cp

copy

copy a file from one location to another

mv

rename, ren, move

moves a file to a new location, or renames a file

rm

del

remove (= delete) a file

mkdir

md

create a new directory

rmdir

rd, rmdir

remove a directory

Creating Files And Folders

Now that we have a good understanding of how to change directories and navigate in Terminal, let's see how we can create our own folders and files. To create a folder we use the mkdir command (short for "make directory"), followed by the name (or space-separated names) of the folder(s) that we would like to create. So let's head over to our Desktop and create a new folder called first_folder.

cd /Users/$USER/Desktop
mkdir first_folder

Whoa...you should be asking yourself, what is that $USER thing? It is an environment variable in your shell that keeps track of the current user of the shell. You can also see who $USER by typing echo $USER or by using the command whoami. Try out both methods of checking who the current user is.

As another side note, this tutorial will use absolute paths to navigate, just to make it easier for you to follow along. However, don't feel like you MUST use absolute paths over relative ones.

Now that we made the first_folder, how do we change directories into it? If you are thinking of the cd command, you're right! So let's cd /Users/$USER/Desktop/first_folder. Or, if you are already in your Desktop, you can just cd first_folder.

We just mentioned "if you are already in your Desktop." How do you know which directory you are in if you forget? Thankfully, there is a handy command called pwd which will display the absolute path and let you know what current directory you are working in. So if you are ever unsure, just type in pwd (which is short for present working directory).

Now that we are inside our new folder, first_folder, let's create a new file. A simple way to create a file is with the touch command. The touch command simply creates an empty file. Let's create a file called first_file: touch /Users/$USER/Desktop/first_folder/first_file. Alternatively, if you are currently in the first_folder directory, you can simple type touch first_file. Now use the ls command to verify that your file was created. ls, which is short for "list," will list all of the files and folders in your current directory.

Displaying Contents Of A File

A very common command to display the contents of a file is the cat command. If you type cat NAME_OF_FILE you can see the contents of the file easily, right there in Terminal. Try it out on the file you just created, first_file. You should see no output after pressing enter. There is no output because first_file is empty.

Let's add some text to the file so that we can use cat. Type:

echo "Hello World" > first_file

The echo command simply writes text to the terminal. The > is called a redirect. The > redirects the output from the command on the left side into the file on the right hand side. We will see more redirects in the next chapter.

Now try using cat on the file again. Do you see Hello World?

There are other ways of seeing the contents of a file in the terminal. Try using the command less: less first_file. less is a program that displays the contents of a file and allows the user to navigate up and down through the file or search for text in the file. To exit less, just press q.

Opening up a file

If you would like to open up a file, you can use the open command. So if we want to see the contents of first_file we can do open first_file. The open command is also very useful if you want to open all the files and folders in a directory (using your operating system's user interface). Try typing in open . and see what happens! If you are on Windows, the command to do this is start NAME_OF_FILE

Moving Files And Folders

Now that you understand how to create files and folders, let's move onto another essential operation: moving and copying folders. To move files and folders we use the mv command. Let's try this out!

Head back to the Desktop by typing in cd ~/Desktop and let's make a new file called test.txt (remember that command? If not - stop reading and go through the previous section again). Now on your Desktop you should have a folder called first_folder and a file called test.txt. Our goal is to move test.txt inside of first_folder - let's do that using the mv command. First make sure you are in the Desktop (type pwd to be sure), type mv test.txt first_folder/test.txt, and press enter.

Did it work? You shouldn't see any kind of success message or confirmation from Terminal, but you also should not see an error. This is very common when working with Terminal: you will see error messages if a command is incorrect, but very rarely see a success message. In other words, no news is good news. In this case, to make sure we did the correct thing, let's cd into first_folder and type in ls. We should see test.txt inside of first_folder.

Copying Files and Folders

Sometimes you may want to make a copy of a file or a folder. To copy a file, we use the cp command (short for copy). The general syntax looks like this:

cp PATH_TO_ORIGINAL_FILE PATH_TO_COPIED_FILE

For example, if we wanted to create a copy of test.txt and call it test_copy.txt, we could enter the following command (assuming we're inside of first_folder:

cp test.txt test_copy.txt

If you list all of the files in first_folder, you should now see three text files.

What if you want to copy an entire directory of files? Try moving up a directory from first_folder, and then type cp first_folder first_folder_copy. Uh oh! You should see an error: cp: questions_copy is a directory (not copied).

In order to copy a directory, you need to modify the cp command as follows:

cp -r first_folder first_folder_copy

The -r is called a flag; you can think of a flag for a command as an option that can be passed to that command. To learn more about the flags that you can pass to cp, you can type man cp (man is short for manual, on Windows this command is --help) and use the arrow keys to move up and down. When you're finished, press q to quit.

Deleting Files And Folders

Alright, enough with all of these files and folders, let's get rid of them. Make sure you are inside the first_folder and type rm test.txt. Once again, you shouldn't see much of a response from the terminal, so run a quick ls to make sure that the file is removed. Now that it is gone... where did it go? The Trash? The answer is it is completely removed from your computer. There is no confirmation or undo so be VERY careful when using the rm command. After you have removed this file, go ahead and remove the copied file as well. Finally, remove first_file. Now that the first_folder is empty, let's move up a directory and remove the first_folder directory itself.

Here you may run into a problem. If you try to use rm on a directory, you will see this message: rm: first_folder: is a directory. It turns out that rm is for a file, while the command rmdir is used to remove (empty) directories. So, let's use the rmdir command to remove first_folder. Make sure that there is nothing else inside that folder, or else you will see a message that looks like this: rmdir: first_folder: Directory not empty.

If there is anything inside the folder, you will have to use rm -rf first_folder. Like we saw with cp, the r and f in -rf are examples of flags. How can you learn more about the flags for rm? Go ahead and remove the first_folder_copy directory using rm -rf.

Exercises

Create a file called name.txt.
Try renaming the file to rename.txt using the mv command. What does this tell you about the command?
Using the cp command, make a copy of rename.txt and call it copy.txt.
Remove the file copy.txt.
Create a folder called questions.
Change directories to the questions folder.
Create a file called first.txt.
Create a file called second.txt.
Go back a directory and make a copy of the questions folder and call it questions_copy.
When using cp -r what is the -r called? What does it do?
Delete the original questions folder and the copy.

{ Listing Files and Flags. }

Objectives

By the end of this chapter, you should be able to:

Understand what the ls command does
Define flags and describe how the syntax works
List files using flags

Listing Files

As you saw in the previous chapter, one of the most important commands you are going to be using is ls, which lists the contents of a directory. If you type ls in a directory you will see all sorts of content. For example, typing ls in your home directory will show you all of the files and folders inside of that directory. Typically your home directory contains folders such as Desktop, Documents, Downloads, Music, Pictures, etc.

Sometimes the default ls command does not give us all the information we want. In such cases, we'll need to add some flags to get more details.

Flags

In the previous chapter, we saw how flags could be used to modify the behavior of cp and rm. Flags can change and even enhance commands and are added using a - after the command. Flags are usually represented by single uppercase and lowercase letters. With the ls command, we can pass in the -a flag to list "all" files (including hidden files and folders). If we want the ls command to give us more information about each file, we can pass in the -l flag. To combine flags we can just use one - and pass in each flag. So the command to use ls and show all files and more detailed information about each one would be ls -la.

Using flags for ls will be essential when working with permissions as well as when you start working with git. We will also see many other terminal commands which accept flags later in this course.

{ Terminal Basics Exercises. }

Write the following terminal commands to perform the following tasks:

Part I

make a directory called first
change directory to the first folder
create a file called person.txt
change the name of person.txt to another.txt
make a copy of the another.txt file and call it copy.txt
remove the copy.txt file
make a copy of the first folder and call it second
delete the second folder

Part II

What does the man command do? Type in man rm. How do you scroll and get out?
Look at the man page for ls. What does the -l flag do? What does the -a flag do?
Type the following command to download and save the contents of google.com: curl https://www.google.com > google.html
Use less to look at the contents of google.html.
Look at the man page for less. Read the section on /pattern. Search for the text hplogo in the google.html file.
How do you jump between words in the terminal?
How do you get to the end of a line in terminal?
How do you move your cursor to the beginning in terminal?
How do you delete a word (without pressing backspace multiple times) in terminal?
What is the difference between a terminal and shell?
What is an absolute path?
What is an relative path?
What is a flag? Give three examples of flags you have used.
What do the r and f flags do with the rm command?

Intermediate Level

{ Permissions and Links. }

Objectives

By the end of this chapter, you should be able to:

Determine the permissions set for a file or a directory
Manage and change permissions using chmod
Manage and change users and groups using chown and chgrp
Explain what root is, and the relationship between root and sudo
Create links in the file system using the ln command
Explain the difference between a hard and a symbolic link

Introduction

When you're working in Terminal, you may sometimes find that you're not allowed to do things you want to do. Maybe you're trying to install something, or move a file from one directory to another, and you get an error telling you something along the lines of "permission denied." These sorts of permissions errors are extremely common, so understanding how to deal with them is important. That's what we'll learn how to in this chapter.

Users and Groups

Before you learn about permissions, you first need to understand users and groups. Let's take a look at an example. Head to your home directory and list everything using the ls -lah command. (Not sure what the h flag does? Check the manual!)

The output you get might look something like this:

The details of these files aren't important. What you should see is a bunch of rows of output, one row for each file or directory. Let's figure out what all of this actually means. For instance, here is the line for the .bashrc file from the above screen shot:

-rwxr-xr-x 1 eschoppik staff 67B Aug 29 2014 .bashrc

The third column specifies the username of the user that owns the file. In this case, eschoppik is the owner of the file. The fourth column specifies the name of the group associated with the file. In this case the group staff is associated with the file.

In most Mac systems, users are also members of the staff group. To see which groups you are a member of, type the groups command in Terminal. The staff group will likely be one of the many groups you are in. As we will see next, permissions can be set for the owner of the file, a user that is in a group associated with the file, or a user that is neither the owner nor a member of the associated group.

Permissions

Let's take a look at that .bashrc line again:

-rwxr-xr-x 1 eschoppik staff 67B Aug 29 2014 .bashrc

We've already talked about the third and fourth columns in this output. Now let's talk about the first column. The -rwxr-xr-x refers to permissions of the .bashrc file. Each character of the permissions string, -rwxr-xr-x describes something about the file's permisisons. But what are permissions? A file's permissions is a set of rules that describes which operations a user can or cannot perform on a file or folder. There are 3 types of operations that can be allowed or not allowed:

r - reading the file
w - writing to the file
x - executing the file (we will go into this in more detail soon)

You may be asking at this point, why is the permissions string so long if there are only 3 operations that can be specified? Well, a permissions string describes different types of users that can or cannot perform read, write and execute operations. You may be one of 3 different types of users:

The owner of the file.
Not the owner, but a member of a group associated with the file.
Other. Not an owner and not in a group that is associated with the file

So a permissions string specifies the permissions for all 3 types of users plus an extra character to specify the type (file, folder, etc).

Here is how the above permissions string breaks down:

In other words, this string says that .bashrc is a file, that the owner of the file can read, write, and execute, users in the group can only read and execute, and other users can only read and execute as well.

Changing Permissions

To change the permissions of a file we use the chmod command. For each set of permissions (owner, group, everyone) we can assign a number from 0 to 7. This is called octal (base-8) notation. Here's a table that illustrates what each number means.

Number

Permission

rwx (display in terminal)

none

---

execute

--x

write only

-w-

write and execute

-wx

read only

r--

read and execute

r-x

read and write

rw-

read, write and execute

rwx

So if we want to change a file so that only the owner and group can read, write, and execute, we would type chmod 770 somefile.txt.

If you'd like to be a bit more specific, you can also set permissions using what's called symbolic notation. Here's an example of what that looks like:

chmod ug+rwx,o-rwx hi.txt

This is saying "add read, write, and execute permissions to the user and the group, and remove read, write, and execute permissions from other." While a bit more verbose, it's also a little more descriptive. To see more examples of symbolic notation, check out this article.

If we want to change permissions for a folder, we need to add the -R flag: chmod -R 755 some_folder.

You can read more about chmod here.

Executable Files and Folders

Now let's talk a little bit more about what the x (executable) means for a file or a folder's permissions. If you have executable permissions on a folder, it means that you can cd into it. See what happens with the following commands:

mkdir test_folder
cd test_folder
cd ..
chmod 666 test_folder
cd test_folder

You should see an error saying permission denied. Add the execute permission back to the folder, and then remove the folder.

Now onto executable files. When a file is executable, it can be run from your shell as if it were a program. Let's first create our file. Type the following in your terminal:

echo ls > test.sh
echo pwd >> test.sh
echo pushd . >> test.sh
echo "cd ~" >> test.sh
echo "pwd" >> test.sh
echo popd >> test.sh
cat test.sh

The test.sh file should look like the following now:

ls
pwd
pushd .
cd ~
pwd
popd

(Did you notice that our first echo command used a single arrow (>), while the other commands used two? We'll explore the difference between these two operators in the next chapter!)

Now let's make the file executable and run it. Use chmod to make it executable: chmod 755 test.sh. Next, execute the file by providing a path to the file. In our case, the file is in the current directory, so to execute it, we do the following: ./test.sh. We just made our first executable shell script!

chown and chgrp

Now that we have a clearer understanding of users, groups and permissions, let's take a look at the line from ls -lah again:

-rwxr-xr-x 1 eschoppik staff 67B Aug 29 2014 .bashrc

The 1 refers to the number of files (this will always be 1 for files)
eschoppik is the "owner"
staff is the group
67B is the size of the file
Aug 29 2014 is the last day the file was modified
.bashrc is the name of the file

So what if we don't want eschoppik as the owner of the file any longer? Or what if we want a different group to own that file? We can use one of the following commands:

chown anotheruser:anothergroup .bashrc

Or if we just want to change the group:

chgrp anothergroup .zshrc.

Now let's take a look at this line from the ls -lah command:

drwxr-xr-x 6 root admin 204B Oct 20 2015 ..

The other file said eschoppik for user and staff for group, but this one says root and admin. We can also see that this is a directory because it starts with a d before listing the permissions. So what is the root user?

root user and sudo

The root user is a special user on your computer that has the power to do anything it wants. It can change permissions on any file, delete anything it wants, etc. When you see root as the owner, and you want to make a change to that file, you have to use a command called sudo. The sudo command gives you the powers of the root user for just one command and will ask you for your password in order to preform the command. Try out commands with sudo. Create a file called somefile.txt. Then make the owner the root user:

sudo chown root somefile.txt

Now try to delete the file without using sudo. You are not allowed. Look at the permissions. Why is this not allowed?

Links

Since we have files and folders located all over our file system, it becomes difficult to identify where many of these are located. Fortunately, we can create a link (also known as an alias) to a file or folder using the ln command. The structure looks like this:

ln path_to_link name_of_link

There are two kinds of links we can make, hard and symbolic links - let's see how they work!

Hard Links

Let's create a file called learn.txt in our Desktop folder (type in cd /Users/$USER/Desktop if you need to get there). We can open up our learn.txt file using open learn.txt and let's add the text "Learning about links!".

Now let's create a link to this file! We can call our link first_link. To do this we use the ln command and type ln learn.txt first_link. Now if we cat first_link we should see the output "Learning about links!".

If we decide to move our learn.txt file anywhere we still have a link to it through first_link! Pretty awesome!

If we decided to delete our learn.txt file, what happens to our hard link? Let's rm learn.txt and then cat first_link. We still see that we have a link! This might seem strange; shouldn't a link be broken if a file is removed? Not with hard links! You can think of a hard link like a direct copy of a file. If the file is removed, the link still exists.

Symbolic Links

We saw that when we remove the original file, any hard links still remain and contain the entire source file. This is usually not what we want, since we usually want a reference to some file and not a direct copy. To create a reference instead of a copy, let's make a symbolic link.

To create a symbolic link, we use the -s flag when creating a link. Let's create a new file called learn_again.txt and then create a symbolic link using ln -s learn_again.txt first_sym_link. If we cat first_sym_link we do not get any errors! But if we delete or move learn_again.txt, our first_sym_link will be broken!

We can also use symbolic links for folders as well, which makes it very useful if we need to access a folder but do not remember the path. However, if your original file/folder path changes or is removed , the symbolic link will break!

{ Redirection. }

Objectives

By the end of this chapter, you should be able to:

Explain what redirection is
Explain the difference between >, >>, and <
Use redirection to work more effectively in Terminal

Redirection

Sometimes instead of simply displaying the output from a command to the terminal, it's useful to take the result output of a command and send it somewhere else. We call this "redirection" and it is denoted by >> or >. Let's start with a simple example using the echo command.

The echo command is useful for displaying text to the terminal, but many times it is more useful to take that text and redirect it to a file. In Terminal, type the command echo Hello World > hello.txt. Then, using the cat command, let's see what we just did by typing cat hello.txt. All we did here is take the text "Hello World" and instead of displaying it to the terminal, we sent it to a file called hello.txt!

Run the same command again but with slightly different text: echo Hello Universe > hello.txt. Now cat the file again. Notice that your new text completely overwrote the old text: you should see that "Hello World" has been replaced by "Hello Universe." In other words, when you use >, whatever text you're echoing into the file will completely overwrite any text that might already be in the file.

Maybe this is what you want, but maybe not. What if you're trying to append some text to the end of the file, rather than overwriting the text? In this case, use >> instead. Try it out: echo Hello World >> hello.txt. Now cat the file. You should see the following:

Hello Universe
Hello World

One very common use case for redirection is to put small pieces of text in a file. Instead of opening a text editor, typing in some text, saving it and closing the file we can do this all in one step.

Redirection with Input

So far we have seen redirection using > and >>. These arrows indicate redirection with standard output (take something and output it to something else). However, we can also use redirection with input as well using the < arrow. Let's use a command called sort, which sorts a file alphabetically. Imagine we have a file called names.txt with the following names:

Bob
Tom
Jim
Amy

If we want to sort this file, we can type sort names.txt and it will output

Amy
Bob
Jim
Tom

Now what if we want to take the contents of names.txt, redirect that to the sort command, and then send that output to a file called sorted.txt? The redirection will look like this: sort < names.txt > sorted.txt. This will now create a new file called sorted.txt with the names sorted alphabetically!

This might seem a bit strange, but try typing these commands and see what information you can output and redirect. As we see right now, we are only using the sort command, but what would happen if we wanted to use other commands along with sort? We would somehow need to connect each of these commands together. We connect these commands together through something called "pipes."

{ Piping. }

Objectives

By the end of this chapter, you should be able to:

Explain what the head, tail, sort, uniq, wc and grep commands do
Define what piping is
Understand use cases for piping
Use piping to better work in Terminal

Piping

At the end of the last chapter, we saw how we could use redirection to combine a couple of commands into one. In that case, in a single line we were able to both sort a text file and output the contents to a new file.

But what if we want to chain even more commands together? This is where piping comes into play. Before we learn about piping, though, let's learn/review a couple other terminal commands.

head - display the first lines of a file (using the -n flag we can specify the number of lines)

tail - display the last lines of a file (using the -n flag we can specify the number of lines)

sort - sort lines of a text file

uniq - removes duplicated lines (your data must be sorted for this to work)

wc - word, line, character and byte count

Now let's create two files - first.txt which contains the text

First
Second
Third

And second.txt which contains:

Fourth
Fifth
Sixth

If we want to concatenate (join) these two files together, we use the cat command:

cat first.txt second.txt (make sure the files and commands are separated by a space).

But what happens if we want to concatenate these two files and then find the word count? What if we want to concatenate and then sort it? This is where we need piping! You can think of a pipe as a connection between the output of one command into the input of another command. So once we concatenate two files we then want to send (or pipe) the result of that to another command. We can even combine this with redirection!

To pipe a command we use the | character. So if we want to pipe cat into sort it would look like this:

cat first.txt second.txt | sort or cat first.txt second.txt | sort | head -n 2

Take a look at this command and try to figure out what it's doing. You'll find a step-by-step answer below.

cat first.txt second.txt | sort | tail -n 3 | head -n 1

Concatenate the two files first.txt and second.txt
Sort the results
Find the last 3 lines
Find the first line of those last 3 lines

This is how we can find the third from last line in a file (without knowing how many lines the file has).

`grep`

Let's examine another useful command called grep which is extremely powerful for finding text. On its own it is helpful, but it is quite useful when piped with cat. Let's try a simple example with cat first.txt | grep First - what do you see?

You should see the word First output to the terminal. This is because grep searched the file for the text First and found a match!

Notice that if grep doesn't find a match, it won't output anything. If it finds multiple matches, it will print them all. Try out these commands and see what grep returns to you!

cat first.txt second.txt | grep Nope
cat first.txt second.txt | grep th

Let's look at another example. Imagine you have a file called petnames.txt, and inside you have the following list of names:

Lassie
Moxie
Whiskey
Fido
Lassie
Moxie

We see here there are quite a few duplicates, so let's try to use the uniq command to remove these duplicate names. The problem is, when we run uniq petnames.txt we get the following

Lassie
Moxie
Whiskey
Fido
Lassie
Moxie

If we look back at our definition of how the uniq command works, we see that our data must be sorted! So how can we first use sort on petnames.txt then attach the uniq command? Piping to the rescue!

sort petnames.txt | uniq gives us

Fido
Lassie
Moxie
Whiskey

This looks great! But this text is just being output to the terminal, what if we want to output this text to a new file called petnames_sorted.txt? We can combine piping with redirection and use sort petnames.txt | uniq > petnames_sorted.txt. Now if we cat petnames_sorted.txt we should see our four unique sorted names!

{ Permissions, Redirection, and Piping Exercise. }

Part I (Permissions and links)

Write terminal commands to do the following:

Create a file called restricted.txt.
Change the permissions on the restricted.txt file to allow the owner to read and write to the restricted.txt file. Do this using the Octal Notation.
Change the permissions on the restricted.txt file to only allow the owner, group and everyone to read and write and execute the restricted.txt file. Do this using the Symbolic notation.
Create a folder called secret_files. Inside the secret_files folder create a file called first_secret.txt and another folder called classified. Inside of the classified folder create a file called super_secret.txt.
Change the permissions on the secret_files to only allow the owner and group to read, write and execute in all the files and folders inside of secret_files. Do this using the Octal Notation.
Create a hard link for the restricted.txt called hard_link.
Create a symbolic link for the classified folder called classified_link.

Part II (Piping and Redirection)

For the following exercises, create a text file called vegetables.txt with the following text:

Lettuce
Amaranth
Beet
Celery
Kale
Dill
Cabbage
Broccoli
Lettuce
Amaranth
Beet
Spinach
Chard
Broccoli
Cabbage
Dill

Write the following terminal commands to do the following

Sort vegetables.txt.
Count the number of lines in vegetables.txt.
Create a file called vegetables_sorted.txt which contains all the unique vegetables sorted in ascending order in vegetables.txt (do this without the touch command).
Create a file called last_three.txt which contains the last three vegetables in the vegetables.txt file (do this without the touch command).
Count the number of lines the word "Broccoli" appears on (using wc and grep).

Development Tools

Visual Studio Code

Visual Studio Code or VS Code is an IDE. IDE stands for Integrated Development Environment. It is the software that you will be using to write most of your code. It is designed to help you develop your apps quickly, focusing on the problems that you need to solve instead of having to search online for minor details.

Auto-complete

One of the most important features of an IDE is that it provides auto-completion. This means that it will give you suggestions of what you can write next, while you are typing something.

For example, when writing a CSS property, VSC will tell you what values you can assign to this property.

File tree view

The reason why we call an IDE integrated is that you almost don't need to leave the window when you are write your code. For example, creating, renaming and moving files can be done directly from the IDE. This functionality can be achieved from something called a tree view. You can find this view on the left side of your IDE.

Finding files

When working with big projects, you will often need to find a file quickly, without having to go through the tree view manually.

Enable formatting on save

To automatically give your code the right format:

In Visual Studio open the settings file (see https://code.visualstudio.com/docs/getstarted/settings#_creating-user-and-workspace-settings)
Search for editor format
Set editor.formatOnSave and editor.formatOnPaste to true

{ OPTIONAL } Visual Studio Code Extensions For Web Development

Visual studio code offers a wide range of extensions. Here is how to install the extension.

Press SHIFT+COMMAND (or Windows)+X or just click on the extension icon of visual studio code. Search for the extension and press install

Here are some visual studio code extensions for web development. The choices of the extension are ones personal opinion.

1: Javascript (ES6) Code Snippets

No need to mention that JavaScript is the core of web development. There are lots of code snippets that we used on a daily basis and this extension helps you by not writing that repetitive code again and again.

It provides JavaScript, TypeScript, Vue, React, and HTML code snippets. This is a must-have extension for web development.

Link: https://marketplace.visualstudio.com/items?itemName=xabikos.JavaScriptSnippets

You can install it by searching the name on the extension section of the visual studio code.

2: CSS Peek

As its name suggests, this extension lets you jump to the CSS code using classes and IDs.

Link: https://marketplace.visualstudio.com/items?itemName=pranaygp.vscode-css-peek

You can install it by searching the name on the extension section of the visual studio code.

3: Auto Close Tag

This extension automatically adds the closing tag of HTML and XML.

Link: https://marketplace.visualstudio.com/items?itemName=formulahendry.auto-close-tag

You can install it by searching the name on the extension section of the visual studio code.

4: ESLint

ESLint is the linting utility for JavaScript. It checks your code for common errors and lets you know in the editor itself. It’s like a virtual peer who is validating your code while you are writing it.

Link: https://marketplace.visualstudio.com/items?itemName=dbaeumer.vscode-eslint

You can install it by searching the name on the extension section of the visual studio code.

Before installing ESLint in visual studio, install it as a global package first. npm install -g eslint

5: Prettier – Code formatter

This extension performs the formatting of the JavaScript, CSS, and HTML code.

Link: https://marketplace.visualstudio.com/items?itemName=esbenp.prettier-vscode

You can install it by searching the name on the extension section of the visual studio code.

6: Path Intellisense

Importing code from other files is what everyone does on a daily basis. This extension makes the development time faster by autocompleting file names.

You type the name of the file in statements and it will search and give you suggestions.

Link: https://marketplace.visualstudio.com/items?itemName=christian-kohler.path-intellisense

You can install it by searching the name on the extension section of the visual studio code.

7: GitLens

We use Git almost every day of our life. GitLens is the visual studio code plugin to supercharge git capabilities.

With GitLens, it’s so easy to view code authorship, check commit number, view changes between the last commit and existing changes, and so on

Link: https://marketplace.visualstudio.com/items?itemName=eamodio.gitlens You can install it by searching the name on the extension section of the visual studio code.

8: Project Manager

Do you work on multiple projects and switch back and forth? I know I do and the project manager has been a savior to manage multiple projects in visual studio code

Link: https://marketplace.visualstudio.com/items?itemName=alefragnani.project-manager

You can install it by searching the name on the extension section of the visual studio code.

9: Live Server

Live Server extension provides the live preview of your web application right within the editor.

This is very handy and useful for the front end developers.

Link: https://marketplace.visualstudio.com/items?itemName=ritwickdey.LiveServer You can install it by searching the name on the extension section of the visual studio code.

10: Debugger for Chrome

This extension brought the powerful chrome debugger right into the visual studio code.

It is very useful for front-end developers to perform the testing and debugging.

Link: https://marketplace.visualstudio.com/items?itemName=msjsdiag.debugger-for-chrome You can install it by searching the name on the extension section of the visual studio code.

11: Better Comments

This extension helps you to create more human-friendly and easy-to-read comments

Link: https://marketplace.visualstudio.com/items?itemName=aaron-bond.better-comments You can install it by searching the name on the extension section of the visual studio code.

12: Code time

This extension tracks your development time and provides you with useful stats such as how many hours you have code today etc.

It’s pretty useful to keep track and see the progress. This is not strictly for web development only, anyone can use this extension.

Link: https://marketplace.visualstudio.com/items?itemName=softwaredotcom.swdc-vscode You can install it by searching the name on the extension section of the visual studio code.

13: Settings Sync

I use a different machine for my work and personal use. I use visual studio code in both machines, however, I don’t want to repeat the same steps to configure the editor every time.

Enters Setting Sync extension. It creates and stores your configuration in Github gist and synchronizes wherever you want. Simple and awesome!

Link: https://marketplace.visualstudio.com/items?itemName=Shan.code-settings-sync You can install it by searching the name on the extension section of the visual studio code.

More Resources

It's alright if you get stuck or if something doesn't look right! When that happens, please ask your teachers or classmates for help in Slack, or use the #support-coding channel.

Everything below is optional and not a requirement of our course. Students who like to challenge themselves can continue with the Advanced Level.

Advanced Level - 1 { OPTIONAL }

{ Terminal Environment. }

Objectives:

By the end of this chapter, you should be able to:

Describe what a terminal environment is
Create and modify terminal environment variables, including the PATH
Save environment variables to a configuration file

What is your terminal's environment?

A terminal's environment is a list of settings that can be referenced by programs. To see what your terminal's environment looks like right now, try typing env in your terminal. You should see output similar to the following:

rvm_bin_path=/Users/tim/.rvm/bin
TERM_PROGRAM=Apple_Terminal
GEM_HOME=/Users/tim/.rvm/gems/ruby-2.3.1
TERM=xterm-256color
SHELL=/bin/bash
CLICOLOR=1
IRBRC=/Users/tim/.rvm/rubies/ruby-2.3.1/.irbrc
TMPDIR=/var/folders/5s/zstwqxy52pl_lq_lr3b5v7nc0000gn/T/
Apple_PubSub_Socket_Render=/private/tmp/com.apple.launchd.Q7TcyOvK4P/Render
TERM_PROGRAM_VERSION=361.1
OLDPWD=/Users/tim
TERM_SESSION_ID=281162A1-5C58-4285-9A35-AC9306923C34
USER=tim
__CF_USER_TEXT_ENCODING=0x1F5:0x0:0x0
LSCOLORS=GxFxCxDxBxegedabagaced
PATH=/usr/local/bin:/usr/local/bin:/usr/bin:/bin:/usr/sbin:/sbin:/Users/tim/.rvm/bin
PWD=/Users/tim/Projects/Rithm/prework
.
.
.

Each word on the left side of the equal sign is called an environment variable. The value on the right side is the value of the variable.

Using environment variables

In the terminal, you can see what value an environment variable has by using echo. When referencing an environment variable, you must use the $ as a prefix. In other words, to print the value for the environment variable PWD, the command would be:

echo $PWD

Try that in your terminal. You should get the same output as the output for the command pwd.

Creating environment variables

Now let's make our own environment variable. Go to your home directory and create a folder called Projects. Now let's make an environment variable called PROJDIR (environment variables are usually all caps) that keeps track of the path to your projects directory. To create an environment variable, you can use the export command. On a Mac or Linux machine, the command would be:

export PROJDIR=/Users/tim/Projects

Notice that the $ isn't being used in this case. When you define an environment variable, you do not use the $. Only use the $ when you want to reference the value of the variable.

Now that you've created the environment variable, let's use it:

cd ~
cd $PROJDIR

You should now be in your project directory.

So now we have a great way of saving a useful variable in our terminal's environment, but we have a problem. Every time you close your terminal window, the environmet variables get reset, so the PROJDIR environment variable will be lost! How do we fix that?

Saving environment variables

Now that we know how to create environment variables, we need to learn how to save them so that every time we open a new terminal window, we have those environment variables set. To save environment variables, you need to modify the shell configuration file in your home directory. This file is different depending on what your default shell is. If you are using oh-my-zsh, then your configuration file will be called .zshrc; if you are using bash, then your configuration file will be called .bash_profile.

Open the configuration file for your shell, either .zshrc or .bash_profile. Next, add the following line to your file:

export PROJDIR=/Users/$USER/Projects

Save the file, quit out of all terminal windows, and then open terminal again. Try executing echo $PROJDIR. You should see the path to your projects directory.

We did one other interesting thing here. Rather than using a hard coded path to the projects directory, we used another environment variable to figure out the correct user name. Try typing echo $USER in your terminal. You should see your user name. The important takeaway here is that an environment variable can be defined using other environment variables. For example, if we had a python folder inside of the Projects directory, we may want a variable for that as well. We could definite it like the following way:

export PYTHON_PROJ=/Users/$USER/Projects/python

Or we could use the PROJDIR environment variable that we already have set:

export PYTHON_DIR=$PROJDIR/python

The only catch is that the line for exporting PROJDIR must come before the line using PROJDIR. Otherwise, PROJDIR will not yet be defined when we use it in the PYTHON_DIR definition.

The `PATH` environment variable

An important environment variable to know and understand is the PATH. Your terminal uses the PATH environment variable to find programs to execute. Try the following in a new terminal window:

export PATH=

Now try using ls in the terminal. It doesn't work! Try a few other commands like man or chgrp. None of them work. That's because commands like ls are just programs stored in a file somewhere in your filesystem. The reason we don't normally need to give the full path to the ls command when we use it is because ls is a file found in one of the folders that are specified on the path.

Open a fresh terminal window. The ls command should be working again. Now use the which command to see where on the path ls is coming from:

which ls

Typically, the ls command is located in the /bin directory (though if you're using oh-my-zsh, the command may be aliased to ls -G). Let's change our PATH environment variable again, but this time, let's assign it to /bin:

export PATH=/bin

Now try to use the ls command. It should still work! That's because ls can now be found in one of the folders of the PATH, specifically in /bin. Other commands still don't work however. The man command still isn't working because it is not found on the PATH. Let's add a few more directories to the PATH in the same terminal window. We want to add /usr/bin, /usr/sbin, and /sbin, but we don't want to rewrite the PATH variable completely. Instead, let's add to the PATH that already exists. In order to do that, we reference the PATH environment variable using the $ and separate multiple paths using a colon:

export PATH=$PATH:/usr/bin:/usr/sbin:/sbin

Now if you do echo $PATH, you should see the following output:

/bin:/usr/bin:/usr/sbin:/sbin

And commands like man should work. Now that you understand the PATH, close the terminal window and open a fresh window, so that your PATH will be set up correctly.

{ Processes. }

Objectives

By the end of this chapter, you should be able to:

Define what a process is
Examine processes that are running on your machine
Kill a process using the kill command

What is a process?

A process is a program on your computer that is being run. For example, when you have Google's chrome browser open, that is a process running on your machine. An email application, a terminal window, and even the ls command are also processes when they are being executed on your machine.

The nice thing about processes is that the operating system ensures that all of the memory for one process cannot be accessed by another process. In other words, if one process crashes, it should not have any effect on the rest of the system.

But how can you tell which processes are running at any given time? And how can you stop a process from the terminal?

`ps`

The ps command is a useful tool for seeing which processes are running on your machine. You can execute the command ps on its own, but more commonly you'll see the command ps aux being used. The a indicates that you're interested in all processes, not just process for your current user; u ensures that the process owner will be displayed; finally, specifying x makes sure that you'll see a list of all active processes, not just those attached to a terminal.

(Note: you may be wondering why the command is ps aux, and not ps -aux. For some history on the command, check out this Stack Overflow question.)

Try typing ps aux in your terminal and see what you get. You should see something similar to this:

USER   PID  %CPU %MEM      VSZ    RSS   TT  STAT STARTED      TIME COMMAND
tim  74874   8.3  1.7  3408348 139912   ??  S     3:34PM   6:39.74 /Applications/Google Chrome.app/Contents/Versions/53.0.2785.116/Google Chrome Helper.app/Contents
tim  74858   6.2  2.8  3224740 233060   ??  S     3:34PM   8:34.62 /Applications/Google Chrome.app/Contents/MacOS/Google Chrome
tim  61431   2.5  0.6  2698840  53728   ??  R     9:46AM   0:59.49 /Applications/Utilities/Terminal.app/Contents/MacOS/Terminal

Some important columns are USER, PID, and COMMAND. The USER column is the username of the user who executed the process. The PID column is a number that uniquely identifies the process. This PID will be useful very soon when we learn how to stop a process.

`kill`

At times you may have a process that for whatever reason is not responsive. In other words, the process continues to execute when you do not want it to. We can stop the process from running by using the kill command.

Let's try it out. First, open any file in terminal using the less command. The process will continue to run as long as you have not pressed q to quit. In a separate terminal window, type the following:

ps aux

Now scroll through the list until you find a process that is running that has been started by your username and whose command's path ends with less. Once you've identified the process, take note of the PID.

Next, to kill the process, type kill and then the PID and hit enter. For example, if your process looks like the following:

tim             10011   0.0  0.0  2434948    900 s000  S+    5:32PM   0:00.00 less readme.md

Then your PID is 10011. So to kill less, your command would be the following:

kill 10011

After killing the process, you should see your terminal window that was running less go back to a normal terminal prompt.

`kill` vs. `kill -9`

Sometimes when you're reading tutorials and a process needs to be killed, you'll see that the command kill -9 is executed, not kill. So what's the difference between these two?

Whenever you try to kill a process, a signal is sent to that process telling it to terminate. By default that signal is the TERM signal. However, if a program has crashed or is frozen for some reason, it's possible that it won't pick up on that signal and the process may not terminate. The -9 flag sends a different signal to the process: according to the manual for kill, -9 represents the KILL signal, which is a "non-catchable, non-ignorable kill." If killing a process doesn't work, try killing with -9 and see if that gets the job done.

For more on kill and the different signals you can send, check out this superuser question.

{ Finding Files and Folders. }

Objectives

By the end of this chapter, you should be able to:

compare and contrast find and grep
use find to search for files and folders
use grep to search for patterns in a string or text
define what a regular expression is

`find`

One of the most useful terminal commands is the find command. When you know how to use it well, you can easily find files on your computer without using Spotlight, Alfred or any other GUI. Let's get started by learning how the syntax works.

To find a specific file in your current directory, you can simply type find and the name of the file. (If you try to find a folder you will find all of the contents inside as well.) For example, if try typing the following command from your home directory:

find Downloads

You should see a list of all your Downloads in the terminal.

To find something with a bit more complexity, use the following pattern

find
a filepath
an expression (this is where you have the most flexibility)

Let's cd into a folder called views and try this pattern to find anything with the name first.txt inside of the views folder:

find . -name "first.txt"

Now this is nice if we know exactly the name of the file we are looking for, but many times we need to use wildcard characters including *, ? and []. The difference between these characters is as follows:

* - any number of characters ? - one character [] - any of the characters inside the brackets

Here are some more examples:

find inside of the views folder (assume we are inside the views folder) anything that ends with .html => find . -name "*.html"
find inside of the views folder (assume we are inside the views folder) anything that ends with a three letter file extension like .txt or .css => find . -name "*.???"
find inside of the views folder (assume we are inside the views folder) anything that starts with the letter f t or s => find . -name "[fts]*"
find inside of the views folder anything that has the text main somewhere in the filename (this could be the beginning as well) find . -name "*main*"

`grep`

Another extremely useful tool for finding information that we've seen before is grep. While find is for files and folders, grep is excellent for searching for specific values in a string or in a text file. If you type grep on its own, it's not that valuable because you need to make sure you pass a filename and text to it. You can also use grep with piping and cat.

We have already seen examples using grep with cat to find words like cat people.txt | grep Elie to find if the word Elie exists in the people.txt file. Let's use the file below which we will call names.txt as an example:

Lisa
Mark
Elie
Beth
Tim
Elizabeth
Tom
Matt
Liza
Janey
Jane
Shana

Let's add a little more onto our knowledge of grep and introduce some flags.

-i for case insensitive search

grep -i "elie" names.txt => Elie

-w for full word search

grep -i "beth" names.txt

Beth
Elizabeth

grep -iw "beth" names.txt => Beth

-A display a certain number of lines after

grep -A 3 "Beth" names.txt

Beth
Tim
Elizabeth
Tom

-B display a certain number of lines lines before

grep -B 3 "Beth" names.txt

Lisa
Mark
Elie
Beth

-C display a certain number of lines lines around

grep -C 3 "Beth" names.txt

Lisa
Mark
Elie
Beth
Tim
Elizabeth
Tom

-v invert pattern (you can think of this as anything NOT what you are searching for)

grep -v "Jane" names.txt

Lisa
Mark
Elie
Beth
Tim
Elizabeth
Tom
Matt
Liza
Shana

-c count matches

grep -c "Jane" names.txt => 2

-n show line number

grep -ni "Jane" names.txt

10:Janey
11:Jane

There are many more flags with grep; you can google around for more or look at man grep.

Wildcards with `grep`

We previously saw wildcards with find, so how can we use them with grep? The key is to use regular expressions. Regular expressions are used to define patterns in a string of characters, which are then used to search a text for potential matches. Regular expressions are common and quite powerful: you can use them to check whether a user has submitted a properly formatted email address or phone number, for instance.

We will not go in depth with regular expressions here. There are a number of great interactive references online. For now, but let's just take a look at a couple examples of the syntax:

. - matches any character

Example: How many names have a full name that is four characters long?

grep -wc "...." names.txt => 7

* - match zero or more of the preceding character or expression.

Example: How many names start with a capital T?

grep -wc "T.*" names.txt => 2

[] - any specific characters

Example: How many names start with a capital L, M, or E?

grep -wc "[LME].*" names.txt => 6

[^] - do not match

Example How many names do not start with a capital T?

grep -wc "[^T].*" names.txt => 10

{ Advanced Terminal - 1 Exercises. }

Part I

Answer the following questions:

Create an environment variable called FIRST_NAME and set it equal to your first name (this does not need to be permanent)
Print the FIRST_NAME variable
Print out the $PATH variable
What is the $PATH variable?
Why would you want to create an environment variable?
How do you permanently save environment variables?
What is a process?
How do you list all processes running on your machine?
What is a PID?
How do you terminate a process?
What is the difference between kill and kill -9?
What grep flag allows for case insensitive search?
What grep flag allows for a certain number of lines before the match?
What grep flag allows for a certain number of lines around the match?
What grep flag allows for a certain number of lines after the match?
What grep flag allows for full word search?
What grep flag shows you the line number of a match?

Part II

Write the following terminal commands to do the following (assume that instructors.txt is an imaginary file):

Find all files inside the Desktop folder that have a name of "learn."
Find all files inside the Desktop folder that start with a "P."
Find all files inside the Desktop folder that end with .txt.
Find all files inside the Desktop/views folder that have the name data somewhere in their filename.
Inside of the instructors.txt file, output the number of times the word "Elie" appears.
Inside of the instructors.txt file, list all matches for any full word that starts with a capital "P."
Inside of the instructors.txt file, list all the line numbers for any full word that starts with a "z" (it should match regardless of upper or lower case).

Advanced Level - 2 { OPTIONAL }

{ SSH. }

Objectives

By the end of this chapter, you should be able to:

set up an EC2 instance on Amazon
use the ssh command to connect securely to a remote server
use the scp command to copy files to a remote server

SSH

SSH, or Secure Shell, provides a secure channel to access other computers. We commonly use SSH to remotely log in and connect securely to other servers. To practice with SSH we will be setting up our own remote servers using Amazon EC2. This setup can be a bit intimidating, but it's a very valuable skill to know with any kind of development. Let's get started!

Setting up an EC2 Instance

As evidenced by the list below, there are a fair number of steps involved in setting up your instance. The links provided also provide a fair amount of context, and help explain the purpose of each of the following steps.

Make sure that you have an Amazon Web Services (AWS) account. You can log in / sign up here and click on the top right.
Create an IAM user here.
Create a key pair here
Create a VPC here
Create a Security Group here
Launch your instance here
Connect to your instance here.

To connect to your instance using SSH you can start here.

Before you try to SSH make sure that your instance is running and that the checks have passed. This should involve typing something along the lines of ssh -i ./me-key-pair-uswest2.pem ec2-user@YOUR_PUBLIC_DNS

Once you've connected via SSH, you can exit out of the shell by typing exit.

Securely copying files to the EC2 Instance with scp

To move files to your EC2 instance, we use the scp command to securely copy information. We will need our pem file that we used before so make sure you know where that is located. The pattern for scp looks like this:

scp -i PATH_TO_YOUR_PEM_FILE FILE_TO_MOVE USERNAME@PUBLIC_DNS

This command would move the file move.txt from my current directory to the home directory on my EC2 instance.

scp -i ./me-key-pair-uswest2.pem move.txt ec2-user@ec2-54-213-7-226.us-west-2.compute.amazonaws.com:/

Terminate your instance

When you are done working on this tutorial - you MUST terminate your instance so that it is not still running. This ensures that you will not be charged for anything as well. You can read more about it here

{ Cut, Sed, Awk, and Xargs. }

Objectives

By the end of this chapter, you should be able to:

Understand what the cut command does and list some use cases for it
Understand what the sed command does and list some use cases for it
Understand what the awk command does and list some use cases for it
Understand what the xargs command does and list some use cases for it

cut

The cut command is very useful for separating or delimiting strings and characters. If you need to split apart text files or find certain characters, cut is the way to go. Let's see how it works with a few examples in a file called languages.txt:

languages.txt

Java,James
Ruby,Matz
Lisp,John
Bash,Brian
Self,David

Here's an example using cut to grab the first 4 characters of each line (the -c flag indicates that the numerical range coming after the flag is referencing characters, not bytes):

cut -c 1-4 languages.txt

Java
Ruby
Lisp
Bash
Self

Now let's grab the last names, but not by the number of characters. Instead, let's do this by delimiting (splitting) on the comma

cut -d, -f2 languages.txt

James
Matz
John
Brian
David

So what is the -f2? -f refers to each portion that has been split by the delimeter (-d) flag. So if we just want the names we can do

cut -d, -f1 languages.txt

Java
Ruby
Lisp
Bash
Self

This is much better because if we had languages of different character lengths, cut -c 1-4 languages.txt would not work!

Next, try to use cut to print out just the authors. Then sort them and then return the first two authors!

Here's one solution:

cut -d, -f2 languages.txt | sort | head -n 2

sed

Sed, or Stream EDitor, is one of the much more complex terminal commands, so we will only be going over some simple uses cases. There are many, many things you can do with sed so try to follow these examples and push yourself to keep learning!

Sed is commonly used for finding and replacing text, editing text in a file, and printing certain parts of a file (though it can to much more). Let's start by finding and replacing each comma in the languages.txt file with a colon.

Here's the command:

sed 's/,/:/g' languages.txt

Let's break this down:

sed - the command s - substitute , - our old value, a comma : - our new value g - globally, do this everywhere not just the first match languages.txt - the file we are working with

Here's what the command should output:

Java:James
Ruby:Matz
Lisp:John
Bash:Brian
Self:David

Notice that if you cat languages.txt after running the above sed command, the original file is unchanged. In order to edit the file, we need to use the i flag to edit in place. But if you try running the command with the -i flag you'll get an error about extra characters. Since we are also specifying additional arguments, we need to use the -e flag as well.

sed -ie 's/,/:/g' languages.txt

If you run this command, and then cat languages.txt, you should see that everything has been replaced!

We are just scratching the surface with sed. If you want to learn more about it you can read this and this

awk

Similar to sed, awk is an incredibly powerful text processing tool. In fact, AWK itself is actually a language that can pretty much do any kind of text manipulation you can think of. We will briefly cover awk and go over a few useful commands you can use with it.

Let's start with the simple command awk '{print}' languages.txt. This will simply print out the languages.txt file. But what happens if we want to just print out a certain part of the file? We can also use awk as a delimiter using the -F flag. Let's set : to be our delimiter and just print out the first portion delimited using $1

awk -F ':' '{print $1}' languages.txt

Let's look at another example, using the history command. If you type this into the terminal, you should see a list of your recent commands. Let's use awk to get a history of just the names of the commands we've used, with no further details. When using awk, if the delimiter is an empty space we do not need the -F flag. So if we want to find the commands we recently used we can type history | awk '{print $2}'.

We can also use awk to print out rows and columns. For example, if you type df -h into the terminal you'll see a table withs some information on your hard drive (df is short for display free desk space). Let's pass the result of this command into awk:

df -h | awk 'FNR == 2 {print $4}'

FNR refers to the record number which is usually a line number. Essentially we're telling awk to grab the item in the 2nd row and 4th column of the table, which in this case should be your available disk space.

If you want to read more about awk, check out this tutorial.

xargs

Sometimes you may want to execute the same command for multiple inputs. For instance, maybe you want to search multiple text files for a certain piece of text. This is a case where the xargs command can be quite handy. Here are some example use cases for xargs; each one runs command for a group of files instead of a single one.

find . -name *.html | xargs grep "elie" - look for the text "elie" inside of every single html file in the current folder

ls | xargs wc -l - counts the total amount of lines for each file in a folder

find . -name "*" | xargs open - opens all of the files in the current folder.

find . -name "*.css" | xargs open - opens all css files in the current folder

find . -name "*.html | xargs rm - removes all files that end with .html

ls | xargs -t -I {} mv {} {}.md - adds a markdown file extension to all files (the -I flag replaces occurrences; the -t flag causes the command that gets run for each input to be logged to the terminal before it is executed, which can be helpful for debugging).

You can read more about xargs here

{ Shell Scripting and Vim. }

Objectives

By the end of this chapter, you should be able to:

write simple shell scripts with arguments
use vi to open and edit files

Shell Scripting

So far we have learned how to use terminal commands, but our commands are not dynamic. We know exactly what the filenames are or what we might be searching for. Our commands are also not reusable easily; if the filename changes, we have to write the whole command again. To reduce duplication and perform far more sophisticated commands in the terminal, we can write shell scripts using a language called bash. To get started, let's create a file called first.sh and inside place the following

echo "Hello World"

Now if we try to run ./first.sh it will tell us permission denied: ./first.sh. So we need to make this program executable! Let's change permissions to 755 so that anyone can run this file: chmod 755 first.sh. Now we can run ./first.sh!

Let's make a second script called second.sh. Inside of this file, type the following:

echo Hello $1

What do you think that $1 represents? Let's first chmod 755 second.sh and then run ./second.sh - we should just see "Hello". Now let's try ./second.sh World and we should see "Hello World"! What we just did was pass an argument to our script. Using arguments which start with $1 and continue upward are how we can make more dynamic scripts.

Your turn

Write a script called sum.sh which accepts two arguments and echoes the sum of the two numbers. You might need to do some research here.

Here's a solution:

echo $(($1+$2))

More complex scripts

There is much more we can do with shell scripting, including conditional logic, if statements, and much more. But for now, let's try to write some handy scripts to help us with daily tasks. Very commonly we are searching for a process using ps aux | grep "Something". Instead of typing that whole thing, we could make a script that does that for us and passes in an argument. Let's try that out with a script called process.sh. It might look something like this.

ps aux | grep $1

Now this is useful if we want to search for a process! If you would like to use the script frequently, you will want to make sure it is somewhere in your $PATH. You can also remove the .sh extension if you are doing this.

Vim

Vim is a terminal based text editor. It can be quite intimidating at first, but if you spend the time to learn how to use it, you can become an extremely efficient developer. To open up something in vi, simply type vi NAME_OF_FILE. Once you are in vim you can exit without saving by pressing escape + : + q. If that is not working press escape + : + q!. If you want to quit and save a file you can either press shift + Z + Z or escape + : + w + q!.

When you first get into vim you will be in what is called visual mode. This means that your keyboard will be set for navigating and not for inserting characters; if you type letters and do not see anything being output, do not worry! To make insertions, press i to enter insert mode. Here you can make changes to files and type as you normally would. Just remember, if you want to quit out of a file you have to be in visual mode!

You can get more practice by using vimtutor - just type vimtutor into your terminal and you can get started. Alternatively, if you want a more visual tutorial you can check out Vim Adventures.

{ Advanced Terminal - 2 Exercises. }

Use the following text file to answer the questions

Elie-Schoppik-sushi
Tim-Garcia-gummybears
Janey-Keig-bagels
Colt-Steele-tacos
Matt-Lane-pizza

Replace all of the - with : using sed
Return a file with just the first name and last name separated by a space (you can do this with cut and sed or just sed)

1>>>>2
2>>>>3
3>>>>4
4>>>>5

Using cut print out just the numbers 2, 3, 4, 5. Use xargs to print them all on 1 line
Using xargs in the ./Desktop directory, find all of the files that include the text Welcome
Write a shell script called access_file.sh which accepts one parameter and changes the permissions to 755
Write a shell script called unaccessible_sh.sh which accepts one parameter and changes the permissions to 300
Using sed write the command to replace all instances of the name "foo" with the string "bar" in a file called baz.txt
Write the command to only print out all of the pids using awk
Type in the df -h command - it will show you much space you have on your hard drive. Using the awk command, print out only the first percentage capacity.

PreviousIntroduction Next2 - Git and Github

Last updated 2 years ago

Table of Content

Operating Systems

Unix

Linux

Ubuntu

The Command Line

How do I use the terminal on my computer?

Commonly used commands

Beginner Level

{ Navigating in Terminal. }

Objectives:

What is Terminal?

What is a shell? Bash/ZSH

How Terminal is Structured

Moving Around

Absolute Paths vs Relative Paths

{ Working with Files and Folders. }

Objectives

Creating Files And Folders

Displaying Contents Of A File

Opening up a file

Moving Files And Folders

Copying Files and Folders

Deleting Files And Folders

{ Listing Files and Flags. }

Objectives

Listing Files

Flags

{ Terminal Basics Exercises. }

Part I

Part II

Intermediate Level

{ Permissions and Links. }

Objectives

Introduction

Users and Groups

Permissions

Changing Permissions

Executable Files and Folders

chown and chgrp

root user and sudo

Links

Hard Links

Symbolic Links

{ Redirection. }

Objectives

Redirection

Redirection with Input

{ Piping. }

Objectives

Piping

grep

{ Permissions, Redirection, and Piping Exercise. }

Part I (Permissions and links)

Part II (Piping and Redirection)

Development Tools

Visual Studio Code

{ OPTIONAL } Visual Studio Code Extensions For Web Development

1: Javascript (ES6) Code Snippets

2: CSS Peek

3: Auto Close Tag

4: ESLint

5: Prettier – Code formatter

6: Path Intellisense

7: GitLens

8: Project Manager

9: Live Server

10: Debugger for Chrome

11: Better Comments

12: Code time

13: Settings Sync

More Resources

Advanced Level - 1 { OPTIONAL }

{ Terminal Environment. }

Objectives:

What is your terminal's environment?

Using environment variables

Creating environment variables

Saving environment variables

The PATH environment variable

`grep`

The `PATH` environment variable

`ps`

`kill`

`kill` vs. `kill -9`

`find`

`grep`

Wildcards with `grep`