Navigate Linux and read file content

In this reading, you’ll review how to navigate the file system using Linux commands in Bash. You’ll further explore the organization of the Linux Filesystem Hierarchy Standard, review several common Linux commands for navigation and reading file content, and learn a couple of new commands.

Filesystem Hierarchy Standard (FHS)

Previously, you learned that the Filesystem Hierarchy Standard (FHS) is the component of Linux that organizes data. The FHS is important because it defines how directories, directory contents, and other storage is organized in the operating system.

This diagram illustrates the hierarchy of relationships under the FHS:

Under the FHS, a file’s location can be described by a file path. A file path is the location of a file or directory. In the file path, the different levels of the hierarchy are separated by a forward slash (/).

Root directory

The root directory is the highest-level directory in Linux, and it’s always represented with a forward slash (/).  All subdirectories branch off the root directory. Subdirectories can continue branching out to as many levels as necessary.

Standard FHS directories

Directly below the root directory, you’ll find standard FHS directories. In the diagram, home, bin, and etc are standard FHS directories. Here are a few examples of what standard directories contain:

Pro Tip: You can use the man hier command to learn more about the FHS and its standard directories.

User-specific subdirectories

Under home are subdirectories for specific users. In the diagram, these users are  analyst and analyst2. Each user has their own personal subdirectories, such as projects, logs, or reports.

Note: When the path leads to a subdirectory below the user’s home directory, the user’s home directory can be represented as the tilde (~). For example, /home/analyst/logs can also be represented as ~/logs.

You can navigate to specific subdirectories using their absolute or relative file paths. The absolute file path is the full file path, which starts from the root. For example, /home/analyst/projects is an absolute file path. The relative file path is the file path that starts from a user's current directory.

Note: Relative file paths can use a dot (.) to represent the current directory, or two dots (..) to represent the parent of the current directory. An example of a relative file path could be ../projects.

Key commands for navigating the file system

The following Linux commands can be used to navigate the file system: pwd, ls, and cd.

pwd

The pwd command prints the working directory to the screen. Or in other words, it returns the directory that you’re currently in. 

The output gives you the absolute path to this directory. For example, if you’re in your home directory and your username is analyst, entering pwd returns /home/analyst. 

Pro Tip: To learn what your username is, use the whoami command. The whoami command returns the username of the current user. For example, if your username is analyst, entering whoami returns analyst.

ls

The ls command displays the names of the files and directories in the current working directory. For example, in the video, ls returned directories such as logs, and a file called updates.txt. 

Note: If you want to return the contents of a directory that’s not your current working directory, you can add an argument after ls with the absolute or relative file path to the desired directory. For example, if you’re in the /home/analyst directory but want to list the contents of its projects subdirectory, you can enter ls /home/analyst/projects or just ls projects.

cd

The cd command navigates between directories. When you need to change directories, you should use this command.

To navigate to a subdirectory of the current directory, you can add an argument after cd with the subdirectory name. For example, if you’re in the /home/analyst directory and want to navigate to its projects subdirectory, you can enter cd projects.

You can also navigate to any specific directory by entering the absolute file path. For example, if you’re in /home/analyst/projects, entering cd /home/analyst/logs changes your current directory to /home/analyst/logs.

Pro Tip: You can use the relative file path and enter cd .. to go up one level in the file structure. For example, if the current directory is /home/analyst/projects, entering cd .. would change your working directory to /home/analyst. 

Common commands for reading file content

The following Linux commands are useful for reading file content: cat, head, tail, and less.

cat

The cat command displays the content of a file. For example, entering cat updates.txt returns everything in the updates.txt file.

p.s.

The cat command in Linux is short for "concatenate", which means to link things together in a series or chain. The cat command is one of the most commonly used commands in Unix-like operating systems like Linux. It reads data from files and outputs their contents. It can also concatenate and display the contents of more than one file.

The cat command was part of the early versions of Unix, dating back to the 1970s, and has been a standard part of Unix-like operating systems ever since. The name "cat" for the command comes from its functionality to concatenate files.

head

The head command displays just the beginning of a file, by default 10 lines. The head command can be useful when you want to know the basic contents of a file but don’t need the full contents. Entering head updates.txt returns only the first 10 lines of the updates.txt file.

Pro Tip: If you want to change the number of lines returned by head, you can specify the number of lines by including -n. For example, if you only want to display the first five lines of the updates.txt file, enter head -n 5 updates.txt.

tail

The tail command does the opposite of head. This command can be used to display just the end of a file, by default 10 lines. Entering tail updates.txt returns only the last 10 lines of the updates.txt file.

Pro Tip: You can use tail to read the most recent information in a log file.

less

The less command returns the content of a file one page at a time. For example, entering less updates.txt changes the terminal window to display the contents of updates.txt one page at a time. This allows you to easily move forward and backward through the content. 

Once you’ve accessed your content with the less command, you can use several keyboard controls to move through the file:

Key takeaways

It’s important for security analysts to be able to navigate Linux and the file system of the FHS. Some key commands for navigating the file system include pwd, ls, and cd. Reading file content is also an important skill in the security profession. This can be done with commands such as cat, head, tail, and less.