Prerequisites

• A Linux terminal or Windows Subsystem for Linux (WSL)
• Basic familiarity with using a terminal

Linux file system

A Linux file system is the way Linux organizes and stores files and folders on a computer.

• Everything starts from one root directory: /
• No C: or D: drives — all files, folders, and devices live somewhere under /
• It's a tree structure: / → subdirectories → files
• In Linux, devices and directories are also treated as files — everything is considered a file in the system.
• Paths matter: # Absolute path → starts with / # Relative path → starts from current folder.
• Case-sensitive: file.txt ≠ File.txt
• Permissions exist: Every file has read, write, execute permissions

Important directories

/home → user files
/etc → configuration files
/bin → basic commands
/dev → device files
/var → logs, dynamic data

Basic navigation commands

Viewing Your Current Directory

Command

pwd     # where am I? (print working directory)

Explanation: The pwd command (Print Working Directory) displays the full path of your current location in the file system. For example, it might output something like /home/<username>/


Listing Directory Contents

Command

ls     # list files and folders in the current directory

Example o/p:

Documents  Downloads  my_folder  notes.txt

Explanation: The lscommand shows all files and directories inside your current location. It helps you quickly see what’s available in that directory.

Command

ls -la     # list all files (including hidden) with detailed information

Example o/p:

drwxr-xr-x  5 user user 4096 Apr 27 10:00 .
drwxr-xr-x  3 user user 4096 Apr 26 09:00 ..
-rw-r--r--  1 user user   45 Apr 25 14:20 notes.txt
drwxr-xr-x  2 user user 4096 Apr 27 09:50 my_folder
-rw-r--r--  1 user user  220 Apr 20 08:00 .bashrc

Explanation: The ls -la command lists all files and directories, including hidden ones (those starting with .), in a detailed format. It shows permissions, owner, size, and last modified time for each item.

Creating Directory

Command

mkdir my_folder     # create a new directory named "my_folder"

Example o/p:

# (no output if successful)

ls
my_folder

Explanation: The mkdir(make directory) command is used to create a new folder in the current location. If the command runs successfully, it usually doesn’t show any output—you’ll see the new directory when you list files using ls.

Command

# Create main directory structure
mkdir -p ~/code/lab/projects/website
mkdir -p ~/code/lab/documents/reports
mkdir -p ~/code/lab/documents/notes

Example o/p:

# (no output if successful)

ls ~/code/lab
documents  projects

Explanation: The mkdir -p command creates directories, including any parent folders that do not already exist. Here, it creates a nested folder structure in one go.

The ~ symbol means your home directory. For example, if your username is bond007, then ~ represents /home/bond007 . So ~/code means /home/bond007/code .

The -p flag means create parent directories as needed, so even if code, lab, or documents do not exist yet, Linux will create them automatically.

Command

# Create some sample files

echo "Hello World" > ~/code/lab/projects/website/index.html
echo "Project Plan" > ~/code/lab/documents/reports/plan.txt
echo "Meeting Notes" > ~/code/lab/documents/notes/meeting.txt
echo "Todo List" > ~/code/lab/documents/notes/todo.txt

Example o/p:

Explanation: The echo command prints text, and the > symbol redirects that text into a file, creating it if it doesn’t exist (or overwriting it if it already exists).

For example, echo "Hello World" > index.html creates a file named index.html and writes "Hello World" inside it.

Command

ls ~/code/lab/projects     # list files and folders inside the projects directory

Example o/p:

website

Explanation: The ls ~/code/lab/projects command shows the contents of the projects directory without needing to navigate into it. The ~ represents your home directory (e.g., /home/bond007), so this command lists everything inside /home/bond007/code/lab/projects.

Navigating to directories

Command

cd my_folder     # move into the "my_folder" directory

Example o/p:

pwd
/home/user/my_folder

Explanation: The cd (change directory) command is used to navigate between directories in the file system. It changes your current location to the specified folder.

Command

cd ..     # move one level up (to the parent directory)

Example o/p:

pwd
/home/user

Explanation: The cd .. command moves you one level up from your current directory to its parent. The .. represents the parent directory in the file system.

Finding Files with find

The find command is used to search files and directories in Linux based on different conditions like name, type, size, time, etc.

Find by name and Find by type are two most important types of find commands

Find by name

find . -name "file.txt"
find . -name "*.txt"

Find by type

find . -type f     # files only
find . -type d     # directories only

Command

find . -name "*.txt"     # find all .txt files in current directory and subdirectories

Example o/p:

./documents/notes/meeting.txt
./documents/notes/todo.txt
./documents/reports/plan.txt

Command

find ./documents/notes -type f     # find only files inside notes directory

Example o/p:

./documents/notes/meeting.txt
./documents/notes/todo.txt

Explanation: The find command is used to search for files and directories. find . -name "*.txt" searches from the current directory (.) and finds all files ending with .txt. find ./documents/notes -type f searches only inside the notes folder and returns only files (-type f), ignoring directories. The -name option specifies a pattern, and -type f limits the search to files.

Searching File Contents with grep

Command

# Search for "Meeting" in all files under documents
grep -r "Meeting" ~/code/lab/documents

Example o/p:

~/code/lab/documents/notes/meeting.txt:Meeting Notes

Explanation: The grep command is used to search for specific text inside files. The -r flag means recursive search, so it will go through all folders and subfolders inside the given path.

Here, it searches for the word "Meeting" inside ~/code/lab/documents and shows the file name and the matching line where the text is found.

Command

# Search for "Plan" in all .txt files
grep "Plan" ~/code/lab/documents/*/*.txt

Example o/p:

~/code/lab/documents/reports/plan.txt:Project Plan

Explanation: The grep command is used to search for text inside files. Here, it looks for the word "Plan" only inside .txt files located in subfolders of documents.

The pattern */*.txt means:
First * → any subdirectory inside documents (like reports, notes)
Second *.txt → all text files inside those subdirectories

Common Issues and Troubleshooting

Permission Denied: Use ls -la to check permissions. Modify permissions with chmodif necessary.

No such file or directory: Verify the path you entered. Use tab completion to avoid typos.

Command not found: Ensure the command syntax is correct and the required tools are installed.

What I Learned Today

• Navigating directories using cd
• Viewing my current location with pwd
• Listing directory contents with ls
• Finding files using find
• Searching file contents with grep