🧭 What is a Path in Linux?

A path is the location of a file or directory in the Linux file system.

There are two types:

1️ Absolute Path

It starts from the root directory / and shows the complete location of a file or folder, no matter where you are
currently.

📌 Format:

/parent_folder/sub_folder/filename

✅ Example:

cd /home/koushik/projects/devops/

 This path starts from / (root).

 It will always go to the exact location, no matter where you are.

2️ Relative Path 🧭

It is relative to your current working directory.

You don’t start from /, you just give the path based on where you are now.

📌 Format:

folder_name/

✅ Examples:

 cd logs/ → Go into logs directory inside your current directory

 cd ../ → Go one level up

 cd ../../configs → Go up 2 levels, then into configs

🔍 Key Differences:

Feature Absolute Path Relative Path

Starts from Root / Current directory (. or no symbol)

Always valid ✅ Yes ❌ Depends on where you are

Begins with / ✅ Yes ❌ No

Used in scripts Preferred for accuracy Used for short paths inside same folder

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Feature Absolute Path Relative Path

Example /home/koushik/devops/file.txt ../devops/file.txt

🧑‍💼 🎯 Interview-Ready Answer:

"An absolute path is the full path that starts from the root /, like /home/user/file.txt. A relative path is based on
the current location, like ../folder/. DevOps engineers use both depending on whether the script needs a fixed
or dynamic path."

👤 1. Normal User (Regular User)

A normal user is a non-administrative user created to perform limited tasks like reading files, running apps, or
editing their own files.

✅ Characteristics:

 Limited permissions (cannot modify system files or configurations).

 Has a home directory (e.g., /home/koushik).

 Cannot install packages or restart services without sudo.

 Safer to use for daily tasks (avoids accidental system changes).

🔍 Example:

koushik@ubuntu:~$ whoami

koushik

👑 2. Root User (Superuser)

The root user is the administrator of the system.
They have full control over everything — they can install, delete, modify any file, user, or service.

✅ Characteristics:

 Full read/write/execute permissions.

 Can run all commands without restrictions.

 Home directory is usually /root

 Dangerous if misused — a wrong command can crash the system.

🔍 Example:

root@ubuntu:~# whoami

root

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🔐 Switching Between Users:

Command Description

su Switch user (to root if no username)

sudo Run a command with root privileges

sudo su Become root temporarily

exit Go back to normal user from root

🧑‍💼 🎯 Interview-Ready Answer:

"In Linux, a normal user has limited access and can only work in their own space. The root user, or superuser,
has full control of the system and can make administrative changes. We use sudo to safely perform root tasks
without logging in as root directly."

What is sudo in Linux?

sudo stands for “Superuser Do”.

It allows a normal user to run commands with root (superuser) privileges without logging in as the root user.

📋 Syntax:

sudo [command]

🧪 Examples:

Command Meaning

sudo apt update Update package list (requires root)

sudo reboot Restart the system

sudo mkdir /var/log/test Create a folder where only root has permission

sudo useradd devuser Add a new user (admin task)

sudo rm -rf /foldername Force delete system folder (be careful ⚠️)

⚠️Best Practices:

 Only use sudo when needed — it prevents accidental damage.

 Always double-check commands before running with sudo.

 Use sudo -k to clear the sudo timestamp (forces password next time).
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Great! Let’s understand sudo su clearly:

🔄 What does sudo su mean?

✅ It combines two powerful commands:

 sudo – Run a command with superuser privileges

 su (substitute user) – Switch to another user (default is root)

💡 So, sudo su means:

👉 “Run the su command as root using sudo permissions,”

which effectively switches you to the root user shell.

📌 When do you use it?

 When you need to become the root user to perform multiple admin tasks

 Useful for interactive sessions where you're running several commands as root

⚠️Example:

sudo su

🧑‍💻 Output: Your prompt changes to # instead of $, indicating you are now root.

Now you can run any command without typing sudo again for each one.

🚪 To Exit Root:

exit

🔐 Tip for DevOps/Best Practice:

Using sudo su gives full root access, which is not always recommended.
It's safer to use sudo for individual commands unless absolutely needed.

🔍 What does sudo su - do?

sudo su - means:

"Use sudo to run su as root, and start a login shell for the root user."

So, it:

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  Switches to the root user (su)

 Loads the root user's environment variables, path, and settings (-)

✅ Difference between sudo su and sudo su -:

Command What it does

sudo su Switches to root without loading root's environment

sudo su - Switches to root and loads root’s full login environment

🧪 Example:

sudo su -

You'll now be:

 In root’s home directory (/root)

 Using root’s environment and PATH

 Seeing # in your shell prompt

🔐 Why use sudo su -?

✅ Best when:

 You’re doing administrative tasks that rely on root's environment

 You want to simulate logging in directly as root

🚪 To exit:

exit

📁 What is ls Command?
ls stands for “list”.
It is used to list files and directories in the current directory or a specified path.

📌 Basic Syntax:

ls [options] [directory or file path]

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🔍 Basic Examples:

Command Description

ls Lists files/folders in current directory

ls /home/koushik Lists contents of that path

ls Documents Lists files inside Documents folder

✅ Most Commonly Used ls Options:

Option Meaning

-l Long listing format (permissions, owner, date, size)

-a Shows all files including hidden (. files)

-h Human readable size (used with -l) like KB, MB

-R Recursively lists subdirectories too

-t Sort by modification time (latest first)

-r Reverse order of sorting

-S Sort by file size

-i Show inode number of files

-d List only the directory name, not contents

🧪 Examples of Combined Options:

ls -l # Detailed info with size, date, owner, etc.

ls -la # Includes hidden files

ls -lh # Human-readable sizes

ls -ltr # Sorted by time (oldest first)

ls -lhS # Sort by size (largest to smallest)

📦 Real-Time DevOps Usage:

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Use Case Command

Check logs folder size/info ls -lh /var/log

View hidden config files ls -a ~

Explore recursive app folders ls -R /opt/tomcat

See file modified recently ls -lt /etc/nginx/

📌 What is touch Command?

touch is used to create empty files or update the timestamp (access and modification time) of existing files.

🧠 Basic Syntax:

touch [options] filename

✅ Common Use Cases:

Command Description

touch file.txt Creates a new empty file named file.txt

touch a.txt b.txt Creates multiple files at once

touch log.txt If file exists, updates its timestamp

🧪 Real-Time Examples:

touch hello.txt # Creates 'hello.txt'

touch devops1.txt devops2.txt # Creates two files

touch /tmp/mylog.txt # Creates file in another folder

🔁 Timestamp Update:

If the file already exists, touch updates:

 Access time (atime) – last read time

 Modification time (mtime) – last content change

⚙️Useful Options:

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Option Description

-c Do not create a file if it doesn’t exist

-t Set a specific timestamp (YYYYMMDDhhmm)

-r file1 Use timestamp of another file

-a Update only access time

-m Update only modification time

🔧 Examples:

touch -c test.txt # Only update if exists, else do nothing

touch -t 202504290915 my.txt # Set specific date/time

touch -r old.txt new.txt # Set new.txt's time same as old.txt

🔐 Real-time DevOps Use Cases:

Scenario Command

Creating test or log files touch /var/log/test.log

Timestamp syncing for deployment touch -r lastbuild.txt app.js

Script creating temp files touch tempfile.txt

🐱 What is cat Command?

cat stands for “concatenate”.

It is used to display the contents of a file, create a file, or combine multiple files into one.

📌 Basic Syntax:

cat [options] [filename]

✅ Common Use Cases:

Command Description

cat file.txt Shows contents of file.txt

cat > newfile.txt Creates a new file, takes input from user

cat file1 file2 Displays contents of both files

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Command Description

cat file1 > file2 Copies content from file1 to file2

cat file1 >> file2 Appends content of file1 to file2

✍️Example: Create a file

cat > demo.txt

Then type your content and press Ctrl + D to save.

👓 Example: View a file

cat demo.txt

➕ Example: Append to an existing file

cat >> demo.txt

🔍 Useful Options:

Option Description

-n Show line numbers

-b Show line numbers (skip blank lines)

-E Show $ at end of each line

-s Remove extra blank lines

-T Show tab characters as ^I

💡 Examples with Options:

cat -n file.txt # Show contents with line numbers

cat -b file.txt # Skip blank lines while numbering

cat -E file.txt # See line ends with $

💼 Real-Time DevOps Usage:

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Task Command

View logs quickly cat /var/log/syslog

Combine two config files cat a.conf b.conf > final.conf

Check file created by script cat output.txt

📁 What is mkdir?

mkdir stands for "make directory".

It is used to create new directories (folders) in Linux.

📌 Basic Syntax:

mkdir [options] directory_name

✅ Common Use Cases:

Command Description

mkdir devops Creates a directory named devops

mkdir test1 test2 Creates multiple folders at once

mkdir /tmp/logs Creates logs folder in /tmp

⚙️Useful Options:

Option Description

-p Create parent directories if they don't exist

-v Show message for each directory created (verbose)

-m Set permissions while creating directory (mode)

🧪 Real-Time Examples:

mkdir projects # Creates 'projects' folder

mkdir dev logs backups # Creates 3 folders

mkdir -p app/logs/error # Creates full path, even if intermediate folders missing

mkdir -v newfolder # Shows message: mkdir: created directory 'newfolder'

mkdir -m 755 newdir # Creates directory with permission 755

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💼 Real-Time DevOps Usage:

Task Command

Create log folders for app mkdir -p /var/logs/myapp/errors

Organize backups or deployments mkdir /backup/2025-April

Script-based directory creation mkdir -p $HOME/scripts/output

🔐 Notes:

 If the folder already exists without -p, it shows an error.

 mkdir needs write permissions in the parent directory.

What is rmdir?

rmdir stands for "remove directory".

It is used to delete empty directories only in Linux.

📌 Basic Syntax:

rmdir [options] directory_name

⚠️Important Note:

 rmdir only removes empty folders.

 If the directory has files or subfolders, it won’t delete it.

✅ Common Use Cases:

Command Description

rmdir demo Deletes the folder demo if it's empty

rmdir test1 test2 Deletes multiple empty folders

rmdir -p a/b/c Removes directory c, then b, then a if all are empty

🧪 Examples:

mkdir testdir

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rmdir testdir # Works as it's empty

mkdir -p project/code

rmdir -p project/code # Removes 'code', then 'project' if both are empty

🔥 Real-Time DevOps Usage:

Use Case Command

Remove temp empty folders rmdir /tmp/oldbuild/emptyfolder

Clean up unused empty dirs rmdir -p /opt/tools/old/utils

What is rm?
rm stands for “remove”.
It is used to delete files and directories in Linux.

📌 Basic Syntax:

rm [options] file_or_directory

✅ Common Use Cases:

Command Description

rm file.txt Deletes the file named file.txt

rm -r folder Deletes a folder and its contents

rm -f file.txt Force delete without confirmation

rm -rf folder/ Forcefully deletes folder + all inside

⚠️Be Careful!

 rm deletes permanently — no Recycle Bin!

 Especially with -rf, there is no warning.

🔧 Useful Options:

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Option Description

-f Force delete (no prompt)

-i Ask before every delete (interactive mode)

-r Recursively delete directories and contents

-v Verbose mode (shows what is being deleted)

🧪 Examples:

rm report.txt # Deletes a file

rm -i config.json # Asks before deleting

rm -r logs/ # Deletes directory and all inside

rm -rf /tmp/project # Deletes without any prompt (DANGEROUS!)

rm -rv myfolder/ # Verbose recursive delete

💼 Real-Time DevOps Usage:

Scenario Command

Remove old logs rm -rf /var/log/myapp/old/

Delete temporary build folders rm -rf /tmp/build/

Clean unused config files rm -i *.conf

🧠 Bonus Tip: Safe Alternative

Use trash-cli tool in Linux if you want a Recycle Bin-like feature (trash-put, trash-list).

🧾 What is CRUD?
CRUD stands for:
Create, Read, Update, and Delete.

It refers to the four basic operations you can do on data in a database or any storage system (like files, APIs, or
cloud services).

🔠 CRUD Operations Explained:

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Operation Action Example in Real Life

Create Add new data Add a new user to a website

Read View existing data View a user's profile

Update Change existing data Change a user's email address

Delete Remove existing data Delete a user from the system

📂 What is cp?
cp stands for “copy”.
It is used to copy files or directories from one location to another in Linux.

📌 Basic Syntax:

cp [options] source destination

✅ Common Use Cases:

Command Description

cp file1.txt /tmp/ Copy file1.txt to /tmp/ directory

cp file1.txt file2.txt Copy file1.txt and rename it as file2.txt

cp -r folder1 /home/user/ Copy an entire directory (folder1)

⚙️Useful Options:

Option Description

-r Copy directories recursively

-i Prompt before overwriting a file

-u Copy only if the source file is newer than the destination file

-v Verbose mode: show the files being copied

-f Force copy (overwrites files without confirmation)

-a Archive mode: preserves all attributes (recursive, symbolic links, timestamps)

🧪 Examples:

cp file1.txt /tmp/ # Copy file1.txt to /tmp/ directory

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cp -r folder1 /home/user/ # Copy folder1 recursively

cp -i file1.txt backup.txt # Prompt before overwriting

cp -v file1.txt /tmp/ # Copy file with verbose output

cp -u file1.txt /tmp/ # Copy file only if it's newer

cp -a folder1/ /home/user/backup/ # Archive copy (preserves attributes)

💼 Real-Time DevOps Usage:

Scenario Command

Copy logs to backup directory cp -r /var/logs/ /backup/logs/

Backup configuration files before changes cp -i /etc/nginx/nginx.conf /backup/

Deploy updated code files to the server cp -r /local/code/ /var/www/html/

🚨 Caution: Overwriting Files

 Be careful when using cp with files. Without -i, it will overwrite files in the destination without warning.

🌐 What is wget?
wget is a command-line utility used to download files from the web using HTTP, HTTPS, or FTP protocols.

It is widely used for downloading files, webpages, and even entire websites.

📌 Basic Syntax:

wget [options] [URL]

✅ Common Use Cases:

Command Description

wget https://example.com/file.zip Download file.zip from the given URL

wget -O newfile.txt https://example.com/file.txt Download and save as newfile.txt

wget -r https://example.com/ Recursively download an entire website

⚙️Useful Options:

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Option Description

-O Save the downloaded file with a specific name

-r Download files recursively (e.g., an entire website)

-c Continue downloading a file from where it was last stopped (resume)

-q Quiet mode — suppress output (useful in scripts)

-np No parent — avoid downloading files from the parent directory

-P Specify a download directory

--limit-rate=200k Limit download speed to a specific rate (e.g., 200 KB/s)

🧪 Examples:

wget https://example.com/file.zip # Download a single file

wget -O downloaded_file.zip https://example.com/file.zip # Download and rename file

wget -r https://example.com/ # Download the whole website

wget -c https://example.com/largefile.zip # Resume downloading a file

wget -q https://example.com/file.txt # Silent mode, no output

wget -P /tmp/ https://example.com/file.txt # Download to /tmp/ directory

💼 Real-Time DevOps Usage:

Scenario Command

Downloading application source code wget https://example.com/app.tar.gz

Downloading logs from remote servers wget -r https://example.com/logs/

Backup website files wget -r -np https://example.com/backup/

Fetching updates for servers wget -q https://updates.example.com/patches/

🧑‍💼 Interview-Ready Answer:

"wget is a Linux command-line utility used to download files from the web via HTTP, HTTPS, or FTP. It supports
various options like -r for recursive downloading, -O to specify a filename, and -c to resume downloads. It's
commonly used in DevOps for downloading software packages, website files, or backup data."

🌐 What is curl?

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curl stands for Client URL.
It is a command-line tool used for transferring data to or from a server using various protocols like HTTP, HTTPS,
FTP, SCP, SFTP, and more.

curl is more versatile than wget and can be used for interacting with APIs, sending HTTP requests, downloading
files, and more.

📌 Basic Syntax:

curl [options] [URL]

✅ Common Use Cases:

Command Description

curl https://example.com Fetch the content of a URL using HTTP(S)

curl -O https://example.com/file.zip Download a file and save it with the original filename

curl -I https://example.com Get the headers of the HTTP response

curl -X POST https://example.com/api Send a POST request to an API

curl -d "key=value" https://example.com Send data to a server using the POST method

⚙️Useful Options:

Option Description

-O Save the downloaded file with the same name as the remote file

-o Save the downloaded content with a custom filename

-X Specify the HTTP request method (GET, POST, PUT, DELETE, etc.)

-d Send data in a POST request (usually used for API interactions)

-I Fetch only the HTTP headers (no content)

-L Follow redirects (e.g., if the URL is redirected to another URL)

-v Verbose mode, show detailed information about the connection and request

-u Use basic authentication (username:password)

-H Send a custom header in the request

🧪 Examples:

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curl https://example.com # Get content from a website

curl -O https://example.com/file.zip # Download file and save it with the original name

curl -o newfile.zip https://example.com/file.zip # Download and save as 'newfile.zip'

curl -I https://example.com # Fetch only headers from the website

curl -X POST https://example.com/api -d "name=Koushik&email=koushik@example.com" # Send POST request

with data

curl -u username:password https://example.com # Send request with authentication

curl -L https://example.com/redirected-url # Follow redirects until the final URL

💼 Real-Time DevOps Usage:

Scenario Command

Testing an API endpoint curl -X GET https://api.example.com/users/123

Downloading a configuration file curl -O https://example.com/config.json

Sending form data to a server curl -X POST https://example.com/form -d "key=val"

Debugging HTTP response headers curl -I https://example.com

Uploading a file via FTP curl -T file.zip ftp://example.com/upload/

🧑‍💼 Interview-Ready Answer:

"curl is a command-line tool used to transfer data between a client and a server using a variety of protocols
(HTTP, HTTPS, FTP, etc.). It's widely used for interacting with web APIs, downloading files, sending data via POST
requests, and even debugging HTTP responses. It offers numerous options for customizing requests, including
sending headers, following redirects, and authenticating."

🌐 Bonus: curl vs wget

Feature curl wget

Protocols HTTP, HTTPS, FTP, SCP, SFTP, and more HTTP, HTTPS, FTP

Use Case Primarily for APIs and data transfer Primarily for downloading files

Redirects Follows redirects with -L Follows redirects by default

Verbosity Detailed with -v (verbose) Simple, uses -v for verbosity

POST/PUT Supports sending data with -d and -X No native support for POST/PUT

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📌 What is Piping?
Piping (|) allows you to combine commands by connecting the output of one command to the input of another.
This is done using the pipe operator (|).

📌 Basic Syntax:

command1 | command2

 command1 generates output (stdout).

 command2 takes the output of command1 as its input (stdin).

✅ Common Use Cases:

Command Description

`ls less`

`ps aux grep process_name`

`cat file.txt wc -l`

`dmesg tail -n 10`

`echo "Hello" tee file.txt`

⚙️Common Commands Used with Piping:

Command Description

cat Concatenate files and display their content.

grep Search for a specific pattern in the input.

awk A powerful text processing tool.

sort Sort input based on certain criteria.

uniq Remove duplicate lines from the input.

head Display the first few lines of input.

tail Display the last few lines of input.

tee Split output to both a file and the terminal.

wc Word count: Count lines, words, or characters.

🧪 Examples of Piping:
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1. Viewing file content in a paginated manner:

ls | less

 ls lists all files in the directory.

 less allows you to scroll through the output one page at a time.

2. Counting the number of lines in a file:

cat file.txt | wc -l

 cat file.txt displays the contents of file.txt.

 wc -l counts the number of lines.

3. Searching for a process:

ps aux | grep apache

 ps aux lists all running processes.

 grep apache filters and shows processes related to apache.

4. Getting the last 10 system messages:

dmesg | tail -n 10

 dmesg shows system messages.

 tail -n 10 shows the last 10 lines of output.

5. Saving output to a file and displaying it:

echo "Hello, World!" | tee output.txt

 echo "Hello, World!" prints "Hello, World!" to the screen.

 tee output.txt saves the output to output.txt and also displays it on the terminal.

6. Sorting and removing duplicates:

cat file.txt | sort | uniq

 cat file.txt reads the contents of file.txt.

 sort sorts the content.

 uniq removes any duplicate lines.

🧑‍💼 Interview-Ready Answer:

"Piping (|) in Linux allows us to pass the output of one command as the input to another. It’s used to chain
multiple commands together, enhancing the power of command-line operations. For example, you can use ps
aux | grep apache to find Apache processes or ls | less to view directory contents in a scrollable manner."

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🌐 Bonus: Combining Multiple Pipes

You can chain multiple commands together with pipes. For example:

ps aux | grep apache | awk '{print $1, $3, $11}' | sort

This command:

1. Lists processes with ps aux.

2. Filters for apache using grep.

3. Prints specific columns ($1, $3, $11) with awk.

4. Sorts the output.

🔍 What is grep?
grep stands for Global Regular Expression Print.
It is used to search for specific patterns or words inside files or output of other commands .

📌 Basic Syntax:

grep [options] "pattern" filename

 "pattern" → the text or word you are searching for.

 filename → the file where you want to search.

✅ Common Use Cases:

Command Description

grep "apple" fruits.txt Search for the word "apple" in fruits.txt file.

grep -i "apple" fruits.txt Case-insensitive search for "apple".

grep -r "main()" /home/user/code Recursively search for main() in files under the directory.

grep -v "error" logs.txt Show all lines that do NOT contain the word "error".

`ps aux grep apache`

grep "^a" names.txt Show lines starting with the letter "a".

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🛠 Useful Options:

Option Description

-i Ignore case (uppercase/lowercase doesn’t matter).

-v Invert match – shows lines that do not match the pattern.

-r or -R Recursive search in all files and directories.

-n Show line numbers where the pattern matches.

-c Count how many lines match the pattern.

-l List file names with matching lines (not the actual lines).

-w Match the whole word only.

-A N Show N lines After the matching line.

-B N Show N lines Before the matching line.

-C N Show N lines Before and After the match (Context).

🧪 Examples:

1. 🔍 Simple Search

grep "hello" file.txt

Shows all lines in file.txt that contain the word "hello".

2. 🔠 Case-insensitive Search

grep -i "Hello" file.txt

Matches "hello", "Hello", "HELLO", etc.

3. ❌ Invert Match

grep -v "error" logs.txt

Shows all lines that don’t contain "error".

4. 🔢 Line Numbers with Match

grep -n "root" /etc/passwd

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Shows line numbers where "root" appears in /etc/passwd.

5. 🔁 Recursive Search in a Directory

grep -r "def" /home/koushik/python_scripts/

Search for the word def in all files inside the given directory.

6. 📂 Show only File Names with Match

grep -l "database" *.txt

Shows the names of .txt files that contain "database".

🧑‍💼 Interview-Ready Answer:

"grep is a Linux command-line tool used to search for specific words or patterns in a file or output. It’s useful for
quickly finding relevant information, debugging logs, or filtering output. Options like -i, -v, -n, and -r give it
powerful capabilities."

🔊 What is echo?
The echo command in Linux is used to display a line of text or string on the terminal.
It's one of the most commonly used commands in shell scripting and for printing messages.

📌 Basic Syntax:

echo [options] [string or text]

✅ Common Use Cases:

Command Description

echo Hello World Prints "Hello World" to the terminal.

echo $USER Displays the value of the variable $USER.

echo "My name is Koushik" Displays a sentence inside quotes.

echo -n "Hello" Prints "Hello" without a new line at the end.

echo -e "Line1\nLine2" Enables interpretation of escape characters.

echo -e "Name\tKoushik" Adds a tab between "Name" and "Koushik".

echo "This is a test" > file.txt Writes "This is a test" to a file.

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Command Description

🔧 Useful Options:

Option Description

-n Do not print a new line after the output.

-e Enable interpretation of escape sequences like \n, \t, \\, etc.

-E (default) Disable interpretation of escape characters (used to cancel -e).

🔤 Escape Sequences (used with -e):

Sequence Meaning

\n New line

\t Horizontal tab

\\ Backslash

\" Double quote

\a Alert (beep)

🧪 Examples: 1. Basic Text:

echo "Welcome to Linux"

Output:

Welcome to Linux

2. No New Line:

echo -n "Hello"

echo "World"

Output:
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HelloWorld

3. With Newline and Tabs:

echo -e "Name:\tKoushik\nRole:\tDevOps Engineer"

Output:

Name: Koushik

Role: DevOps Engineer

4. Printing Variable:

name="Koushik"

echo "My name is $name"

Output:

My name is Koushik

5. Writing to File:

echo "This is Linux training" > notes.txt

This command writes the message into the file notes.txt. (It will overwrite existing content)

🧑‍💼 Interview-Ready Answer:

"echo is a Linux command used to print text or variables to the terminal. It's widely used in scripting to display
messages or write content to files. With options like -e and -n, you can control formatting like newlines and
tabs."

✂️What is cut?

The cut command in Linux is used to extract specific sections or fields (columns or characters) from each line of
a file or output.

It’s helpful when working with data files like CSV, log files, or command outputs.

📌 Syntax:

bash

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CopyEdit

cut [OPTION]... [FILE]

You can also use cut with output from other commands using pipes (|).

✅ Common Use Cases:

Command Description

cut -c1-5 file.txt Cuts the first 5 characters of each line.

cut -d "," -f2 file.csv Cuts the 2nd column (field) from a comma-separated file.

`cat file.txt cut -d ":" -f1`

cut -f1 file.txt Cuts the first tab-separated field by default.

🟩 Using cut

CopyEdit

cut -d ":" -f1 /etc/passwd

👉 Gets the first field (username) from colon-separated lines.

🟨 Using awk (same result as above)

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awk -F: '{print $1}' /etc/passwd

 -F: → Set delimiter to colon :

 $1 → Print the first field

✅ More powerful than cut because you can use conditions, format, and calculate.

🟦 Using grep (Different Purpose)

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grep "root" /etc/passwd

👉 grep is for searching/filtering lines.

It does not cut or extract fields. It shows full lines that match "root".

🎯 Summary with Examples

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1. 🔍 Extract 2nd Column from CSV

 Using cut:

cut -d "," -f2 students.csv

 Using awk:

awk -F, '{print $2}' students.csv

2. Filter lines with a name:

 Using grep:

grep "Koushik" students.csv

🧑‍💼 Interview Tip:

"cut is used to extract specific fields or characters, while awk is more powerful for extracting, formatting, and
even processing data. grep is used to search lines matching a pattern."

🧠 What is awk?

awk is a powerful command-line tool used for text processing, especially for working with structured data (like
CSV, tab-separated files, logs, etc.).

You can use awk to extract fields, filter rows, and perform calculations.

📌 Basic Syntax:

awk 'pattern { action }' filename

Or with delimiter:

awk -F '<delimiter>' '{ action }' filename

✅ Common Use Cases:

Purpose Example Command What It Does

Print 1st column awk '{print $1}' file.txt Prints first word/field of each line

Print specific column (CSV) awk -F, '{print $2}' data.csv Prints 2nd column (comma-separated)

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Purpose Example Command What It Does

Match pattern and print awk '/Koushik/ {print $0}' file.txt Prints lines containing "Koushik"

Conditional print awk '$3 > 50 {print $1, $3}' marks.txt Print name & marks if marks > 50

Calculate column total awk '{sum += $2} END {print sum}' data.txt Adds up 2nd column values

🎯 Summary with Examples

1. 🔍 Extract 2nd Column from CSV

 Using cut:

cut -d "," -f2 students.csv

 Using awk:

awk -F, '{print $2}' students.csv

2. Filter lines with a name:

 Using grep:

grep "Koushik" students.csv

🧠 What is head?

head command is used to display the first few lines of a file.

✅ Syntax:

head [options] filename

📌 Default:

 By default, it shows the first 10 lines of the file.

📘 Examples:

head file.txt

👉 Shows the first 10 lines.

head -n 5 file.txt

👉 Shows the first 5 lines.

head -n 15 /var/log/syslog

👉 Useful in DevOps to check the beginning of large log files.

🧠 What is tail?

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tail command is used to display the last few lines of a file.

✅ Syntax:

tail [options] filename

📌 Default:

 By default, it shows the last 10 lines.

📘 Examples:

tail file.txt

👉 Shows the last 10 lines.

tail -n 5 file.txt

👉 Shows the last 5 lines.

tail -f /var/log/syslog

👉 -f means follow the file live, used for monitoring live logs (very useful in DevOps).

🔁 Summary Table:

Command Description

head file.txt Show first 10 lines

head -n 20 Show first 20 lines

tail file.txt Show last 10 lines

tail -n 5 Show last 5 lines

tail -f file Live monitor the file (real-time updates)

🧑‍💼 Interview Answer:

"head shows the top lines and tail shows the bottom lines of a file. These are useful for viewing the beginning or
end of logs and files. The tail -f option helps monitor logs in real time, which is commonly used by DevOps
engineers."

Would you like to see a real-time log monitoring example with tail -f?

🧠 What is the find command?

find is a command-line tool used to search for files and directories in a directory hierarchy based on name, size,
type, date, permission, etc.

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It’s very powerful and widely used in real-time DevOps and Linux administration.

✅ Basic Syntax:

find [path] [options] [expression]

📘 Common Examples:

1. 🔍 Find a file by name:

find /home/koushik -name "file.txt"

➡️Searches for a file named file.txt inside /home/koushik

2. 🔍 Case-insensitive name:

find /home/koushik -iname "File.txt"

➡️Same as above, but ignores uppercase/lowercase.

3. 📂 Find all .txt files:

find . -name "*.txt"

➡️Finds all .txt files under current directory.

4. 📁 Find directories only:

find . -type d

➡️Lists all directories.

5. 📄 Find files only:

find . -type f

➡️Lists all files.

6. 🧭 Find files modified in last 1 day:

find . -mtime -1

➡️Shows files modified within the last 24 hours.

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7. 🔒 Find files by permissions:

find . -perm 644

➡️Finds files with permission 644.

8. Find and delete .log files:

⚠️Be careful with -delete

find . -name "*.log" -delete

➡️Deletes all .log files in current and sub-directories.

9. 🧹 Find large files (size > 100MB):

find . -size +100M

➡️Finds files bigger than 100MB.

10. 🔧 Run a command on each file:

find . -name "*.sh" -exec chmod +x {} \;

➡️Makes all .sh files executable.

🧑‍💼 Interview Tip:

"find is a powerful Linux command used to locate files and directories based on name, type, size, date,
permissions, and more. It's commonly used in automation and server maintenance to search and perform
actions on specific files."

🧠 Summary Table:

Option Purpose

-name Match file name

-iname Match name (case-insensitive)

-type f/d File or directory

-size Match file size

-mtime Modified time

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Option Purpose

-perm Match permission

-delete Delete matched files

-exec Run command on each result

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