Welcome back to Day 3 of the #90DaysOfDevOps challenge. In today's session, I will continue exploring basic Linux commands that are essential for any DevOps engineer. These commands will help you navigate and manage your Linux system efficiently. So, let's dive in!

1. Viewing the content of a file

To view the content of a file, you can use the cat command followed by the filename. For example:

cat filename

This will display the entire contents of the file on your terminal. It's a simple and effective way to quickly check the contents of a file.

2. Changing the access permissions of files

The chmod command is used to change the access permissions of files on Linux. It allows you to modify the read, write, and execute permissions for the owner, group, and others.

chmod [options] filename

You can specify different options with the chmod command to set specific permissions. Some common options include:

• u (user/owner): Changes the permissions for the file owner.

• g (group): Changes the permissions for the group associated with the file.

• o (others): Changes the permissions for users who are neither the owner nor in the group.

• + (add): Adds the specified permission.

• - (remove): Removes the specified permission.

• = (assign): Assigns the specified permission.

For example, to give the owner read and write permissions on a file, you can use:

chmod u+rw filename

3. Checking command history

To check the commands you have previously run in your terminal session, you can use the history command. Simply type history in your terminal, and it will display a list of commands along with their respective line numbers.

history

This command is especially useful when you want to recall and reuse previously executed commands.

4. Removing a directory/folder

To remove a directory on Linux, you can use the rmdir command followed by the directory name.

rmdir directory

However, please note that the rmdir command can only be used to remove empty directories. If you want to remove a non-empty directory, you should use the rm command with the -r option, which stands for recursive.

The main differences between rmdir and rm are:

• rmdir can only remove empty directories, whereas rm -r can remove both empty and non-empty directories.

• rmdir is a safer option, as it prevents accidental removal of non-empty directories.

• rm -r is more powerful, but should be used with caution to avoid unintended data loss.

5. Creating a fruits.txt file and viewing the content.

To create a new file on Linux, you can use the touch command followed by the desired filename. For example:

touch fruits.txt

This command will create an empty file with the specified name. To view the content of a file, you can use the cat command we discussed earlier.

6. Adding content in fruits.txt (One in each line) - Apple, Mango, Banana, Cherry, Kiwi, Orange, Guava.

To add content to a file, you can use a text editor like vi or nano. However, if you want to append content from the command line, you can use the echo command and redirect the output to the file.

For example, to add the following fruits to a file named fruits.txt, one fruit per line:

Apple
Mango
Banana
Cherry
Kiwi
Orange
Guava

You can use the following command:

echo -e "Apple\nMango\nBanana\nCherry\nKiwi\nOrange\nGuava" > fruits.txt

• echo: The echo command is used to display text or variables on the terminal.

• -e: This option enables the interpretation of backslash escapes. It allows us to include special characters, such as newline (\n), in the output.

• "Apple\nMango\nBanana\nCherry\nKiwi\nOrange\nGuava": This part of the command represents the text or content that will be added to the fruits.txt file. Each fruit name is separated by the newline character (\n), ensuring that each fruit appears on a new line in the file.

• >: This symbol is a redirection operator that directs the output of the echo command to a file.

• fruits.txt: This is the filename of the file where the echoed content will be saved. In this case, it's fruits.txt.

7. Showing the top three items from a file

To display the top three items from a file, you can use the head command. By default, it shows the first ten lines of a file, but you can specify the number of lines using the -n option.

head -n 3 filename

The head command is particularly useful when you want to get a quick preview of the contents of a large file.

8. Showing the bottom three items from a file

To display the bottom three items from a file, you can use the tail command. Similar to head, the tail command also displays the last ten lines of a file by default. You can use the -n option to specify the number of lines to display.

tail -n 3 filename

The tail command is often used to monitor log files or track real-time changes in files.

9. Creating another file names Colors.txt and viewing the content.

To create a new file and view its content, you can use the touch command to create the file, and then use the cat command to view the contents. For example:

touch Colors.txt
cat Colors.txt

This will create an empty file named Colors.txt and display its content, which, in this case, will be empty.

10. Add content in Colors.txt (One in each line) - Red, Pink, White, Black, Blue, Orange, Purple, Grey.

Similar to adding content to fruits.txt, you can use the echo command to append content to the Colors.txt file.

echo -e "Red\nPink\nWhite\nBlack\nBlue\nOrange\nPurple\nGrey" > Colors.txt

This command will add the listed colors to the Colors.txt file, with each color on a new line.

11. Finding the difference between fruits.txt and colors.txt files

To find the difference between two files, you can use the diff command followed by the filenames. For example:

diff fruits.txt Colors.txt

The diff command will show the lines that are different between the two files, highlighting any changes made.

These are some basic Linux commands that will prove helpful throughout your DevOps journey. Understanding and practising these commands will enable you to navigate and manage your Linux system with ease.

That's all for Day 3 of the #90DaysOfDevOps challenge. Stay tuned for Day 4 of the #90DaysOfDevOps challenge, where I'll explore basic Linux Shell scripting for DevOps Engineers.