Manage directories and files

Previously, you explored how to manage the file system using Linux commands. The following commands were introduced: mkdir, rmdir, touch, rm, mv, and cp. In this reading, you’ll review these commands, the nano text editor, and learn another way to write to files.

Creating and modifying directories

mkdir

The mkdir command creates a new directory. Like all of the commands presented in this reading, you can either provide the new directory as the absolute file path, which starts from the root, or as a relative file path, which starts from your current directory.

For example, if you want to create a new directory called network in your /home/analyst/logs directory, you can enter mkdir /home/analyst/logs/network to create this new directory. If you’re already in the /home/analyst/logs directory, you can also create this new directory by entering mkdir network.

Pro Tip: You can use the ls command to confirm the new directory was added.

rmdir

The rmdir command removes, or deletes, a directory. For example, entering rmdir /home/analyst/logs/network would remove this empty directory from the file system.

Note: The rmdir command cannot delete directories with files or subdirectories inside. For example, entering rmdir /home/analyst returns an error message. 

Creating and modifying files

touch and rm

The touch command creates a new file. This file won’t have any content inside. If your current directory is /home/analyst/reports, entering touch permissions.txt creates a new file in the reports subdirectory called permissions.txt.

The rm command removes, or deletes, a file. This command should be used carefully because it’s not easy to recover files deleted with rm. To remove the permissions file you just created, enter rm permissions.txt. 

Pro Tip: You can verify that permissions.txt was successfully created or removed by entering ls.

mv and cp

You can also use mv and cp when working with files. The mv command moves a file or directory to a new location, and the cp command copies a file or directory into a new location. The first argument after mv or cp is the file or directory you want to move or copy, and the second argument is the location you want to move or copy it to.

To move permissions.txt into the logs subdirectory, enter mv permissions.txt /home/analyst/logs. Moving a file removes the file from its original location. However, copying a file doesn’t remove it from its original location. To copy permissions.txt into the logs subdirectory while also keeping it in its original location, enter cp permissions.txt /home/analyst/logs.

Note: The mv command can also be used to rename files. To rename a file, pass the new name in as the second argument instead of the new location. For example, entering mv permissions.txt perm.txt renames the permissions.txt file to perm.txt.

nano text editor

nano is a command-line file editor that is available by default in many Linux distributions. Many beginners find it easy to use, and it’s widely used in the security profession. You can perform multiple basic tasks in nano, such as creating new files and modifying file contents. 

To open an existing file in nano from the directory that contains it, enter nano followed by the file name. For example, entering nano permissions.txt from the /home/analyst/reports directory opens a new nano editing window with the permissions.txt file open for editing. You can also provide the absolute file path to the file if you’re not in the directory that contains it.

You can also create a new file in nano by entering nano followed by a new file name. For example, entering nano authorized_users.txt from the /home/analyst/reports directory creates the authorized_users.txt file within that directory and opens it in a new nano editing window.

Since there isn't an auto-saving feature in nano, it’s important to save your work before exiting. To save a file in nano, use the keyboard shortcut Ctrl + O. You’ll be prompted to confirm the file name before saving. To exit out of nano, use the keyboard shortcut Ctrl + X.

Note: Vim and Emacs are also popular command-line text editors.

Standard output redirection

There’s an additional way you can write to files. Previously, you learned about standard input and standard output. Standard input is information received by the OS via the command line, and standard output is information returned by the OS through the shell.

You’ve also learned about piping. Piping sends the standard output of one command as standard input to another command for further processing. It uses the pipe character (|). 

In addition to the pipe (|), you can also use the right angle bracket (>) and double right angle bracket (>>) operators to redirect standard output.

When used with echo, the > and >> operators can be used to send the output of echo to a specified file rather than the screen. The difference between the two is that > overwrites your existing file, and >> adds your content to the end of the existing file instead of overwriting it. The > operator should be used carefully, because it’s not easy to recover overwritten files.

When you’re inside the directory containing the permissions.txt file, entering echo "last updated date" >> permissions.txt adds the string “last updated date” to the file contents. Entering echo "time" > permissions.txt after this command overwrites the entire file contents of permissions.txt with the string “time”.

Note: Both the > and >> operators will create a new file if one doesn’t already exist with your specified name.

Key takeaways

Knowing how to manage the file system in Linux is an important skill for security analysts. Useful commands for this include: mkdir, rmdir, touch, rm, mv, and cp. When security analysts need to write to files, they can use the nano text editor, or the > and >> operators.