pwd stands for Print Working Directory.

Some examples of directories in the Linux OS are /root, /boot, /bin, /opt, /run, /usr and /home.

The pwd command tells you the current folder where you are.
The default directory that you start out with is the home directory of the user who is logged in.
If you are the root user, your first directory would be /.
If you are a user named duke, then your home directory would be /home/duke

Type pwd and press enter.

You will find that you are in the / directory as shown below. Note:The hostname (The value after the word [email protected] may be different than what is shown below.) [email protected]:/# pwd /

ls stands for list directory contents.

The ls command displays the names of files contained within a directory, as well as any requested, associated information.

Type ls and hit enter.

You should see several directories. One directory that is of interest that we will use for our learning is the cybershaolin directory.

[email protected]:/# ls bin cybershaolin etc lib media opt root sbin sys usr boot dev home lib64 mnt proc run srv tmp var

cd stands for Change Directory.

Type cd cybershaolin and press enter.

What you just did was you changed your directory to the cybershaolin directory.

You can check by typing pwd and pressing enter.

You will now be in the /cybershaolin directory.

Now type ls and press enter. You will see that there are some files related to superheroes comic companies (e.g., dc and marvel) as well as a villains file that is compressed as a tape archive (.tar file) as shown below.

[email protected]:/cybershaolin# ls superheroes_dc1.txt superheroes_dc2.txt superheroes_dc3.txt superheroes_marvel.txt villains.tar

cd and ../(DotDotSlash))
In order to go to the previous folder, you can use the shortform ../ (DotDotSlash) along with the cd command.
Since you are in the cybershaolin directory now, you can go to the previous directory using the cd ../ command.

mkdir stands for Make Directory.
It is used to create a folder or directory so that you can be organized.

You can think of directories like a bookshelf. In the top shelf you may have your school books, the middle shelf may have some fiction books and the bottom shelf may contain some activity books. So also in a computer system, you can organize your files in directories.

You notice that there are some files in there, but no folders (or directories) to organize them. So let us create two directories to organize these files. The two directories you are going to create are a directory called dc and another one called marvel.

Type mkdir dc and press enter.
What happened? It may seem like nothing happened if your command ran successfully.

To see if your directory was created successfully, you can use the ls command which will list all the contents of the current directory where you are.

Type ls and press enter.

You should see aa directory/folder called dc.

Now type mkdir marvel and press enter.

And is &&
NOTE: You could have also created both the directories in a single command using the && operand. The command in that case would have been mkdir dc && mkdir marvel.

diff or diff3 stands for Difference.

The diff command compares two files line by line. The diff3 command compares three files line by line.

Type ls and press enter.

You see that there are the a few text (.txt) files and the folders that you created.

We need to move the files into the respective directories, meaning the superheroes_dc file need to be moved into the dc folder and the superheroes_marvel file need to be moved into the marvel folder.

But wait, there are three superheroes_dc text files. So which of these files is the correct file that we need to move into the dc directory.

One way we can find out about each of these files is look into the files using the cat command, but that would take time. So we can use the diff or diff3 command.

Type diff3 superheroes_dc1.txt superheroes_dc2.txt superheroes_dc3.txt and press enter.

You will see the contents of the three files that are different from each other line by line.
The first file has the word 'Flash' misspelled as 'F|ash' (note the second letter is a pipe character and not a lowercase 'L').
The third files has the word 'Batmans' and not 'Batman'.
The second file is the only file that has the names of the DC superheroes, correctly spelled.

So we will move the superheroes_dc2.txt into the dc folder and the superheroes_marvel.txt into the marvel folder, but first let us remove the two incorrect files.

rm stands Remove.

To remove the superheroes_dc1.txt file and the superheroes_dc3.txt file, type rm superheroes_dc1.txt && rm superheroes_dc3.txt and press enter.

NOTE: To remove a directory, you will use the rmdir command. If there are files in the directory that you are trying to delete, then your rmdir command will fail and you will see something like
rmdir: failed to remove 'myGames/': Directory not empty

To delete a directory that has content inside it, you can use the rm command along with the operands called -rf which will do a forcefully (-f) remove (rm) the listed directories and their contents recursively.

The DeathStars of the rm Commands Never ever, never ever, never ever run the following command
rm -rf *.*
unless you absolutely know that you are in the directory from which you want to delete ALL folders and files.
The *.* here is a wildcard syntax to mean any files of any type.

mv stands for Move

Now let us organize the files.

Type mv superheroes_dc2.txt dc and press enter.

This command which will move the superheroes_dc2.txt file into the dc folder.

Type mv superheroes_marvel.txt marvel and press enter.

Now type ls and you will find that the text files don't exist as they did before. They have been deleted and moved into the respective directories.

tar stands for Tape Archive

The tar command saves many files together into a single tape or disk archive, and can restore individual files from the archive.

The -x operand is used to extract files from an archive. The -v operand is used to verbosely list the files that are processed. The -z operand is used to filter the archive through gzip, a compression utility. The -f operand is used to use the archive file.

Type ls and press enter.

You will find notice that there is a compression tar file called villains.tar that we would like to untar (uncompress).

Type tar -xzvf villains.tar and press enter.

You will see that the files in the villains.tar archive got extracted into a directory called villains and the name of the file that got extracted into that folder is README.txt (as shown below)
[email protected]:/cybershaolin# tar -xzvf villains.tar villains/ villains/README.txt

cat stands for Concatenate

It is the command that is used to concatenate (read and adds) and print the contents of a file.

The cat utility reads files sequentially, writing them to the standard output (terminal).

To read what the README.txt contents in the villains directory, you can first navigate into the villains directory using the cd command and then use the cat command to read the contents of the README.txt file.

Type cd villains and press enter.

Then Type cat README.txt and press enter.
You will see the following text print on the screen.
The villians list that you are looking for is not here. It must be hiding somewhere. Pay careful attention as you search... for even a dot can mean a lot. Can you try to 'locate' the villains file?

Note: The cat command is used extensively in managing files in Linux.

locate stands for Locate

The message in the README.txt file suggested that the file may be hidden. It also stated that a dot means a lot so let us try to search for the villains fill with a dot in front.

You can use the locate command if you know the name of the file or directory that you are trying to find (locate).

You can try to type locate .villains and press enter to find the hidden villains list.

You should see that a file called .villains.txt is hidden in the /cybershaolin directory as shown below.
[email protected]:/cybershaolin/villains# locate villains /cybershaolin/.villains.txt /cybershaolin/villains.tar

Hidden Files (using ls -a) Files that are named with a dot (.) are hidden and not shown when you run the ls command.
To see hidden files, we need to modify the ls command with some additional information. This additional information that is added to a Linux command is called an operand.

Type ls -a and press enter. The -a operands will list directory entries whose names begin with a dot (.) and are hidden.

file stands for File (Determination)

The file command helps to determine the type of Files.

Because we know that the villains file is in the cybershaolin directory. You have to run cd ../ to go back to the cybershaolin folder since you are inside the villains folder.

Now we learned earlier that in order to read the contents of a file, we can use the cat command.

Type cat .villains.txt and press enter, once you are in the cybershaolin folder.

You will notice that some text is displayed on the screen but it is not humanly readable (kinda looks garbled).

Aha, the villains have not only hidden the file, but also tried to hide (obfuscate) the contents of the file by changing the type of the file.

A .txt file should be able to be opened by the cat command, but since this did not work as expected for us, let us determine the type of the file using the file command.

Type file .villains.txt and press enter.

You will notice that the file type is a zip (compressed) file, with a .txt file extension.

Next we will need to unzip this file to see what the file contains, but before we can do that, we need to rename the file from the .txt extension to the .zip extension.

Rename using Move (mv) To rename the file we will interestingly use the mv command. The mv command that you learned earlier can be used for two reasons.

• Move source(s) to directory and
• Rename the Source to Destination

Type mv .villains.txt villains.zip and press enter to rename the file from .villains.txt to .villains.zip.

Technically what the mv command did in this case was it renamed the villains.txt file to village.zip file.

While we are renaming the villains.txt file we might as well move it to the villains folder.

Type mv villains.zip villains/ and press enter.

unzip stands for Unzip

The unzip command is used to extract all contents of a zipped file.

Since we have a zip file renamed villains.zip in the villains directory, we will navigate into the villiains directory and unzip the villains.zip file.

Type cd villains and press enter.
Type unzip villains.zip and press enter.

You will see this text appear on the screen.

Archive: villains.zip inflating: villains.txt

This is saying that the folder (archive) villains.zip is decompressing (inflating) to reveal villains.txt.

Type ls to see if the villains.txt file is there.

file
Why don't we use the file villains.txt to make sure and guarantee that this is really a text file. You should see villains.txt: ASCII text to show that this truly is a text file.

grep stands for Global Regular Expression Print

We can use the grep command to search specifically for a word or phrase in a text file. If you want to search for one word in a extremely huge document you can use the grep command.

Since we know that this list contains villain names we can search for a villain using the grep command.

Type grep 'Joker' villains.txt to see if the Joker is a part of the villains list.

To see a list of all the villains in the villains.txt file, which of the Linux commands that you have learned can you use?

If you answered cat, you are correct.

Type cat villains.txt and press enter.

In this course, you have learned to use some common linux commands.

The end result of this training kwoon should have all the superhero and villain text files organized in their respective folders as shown below. . .. dc marvel villains villains.tar

Hope you had fun learning! :-)