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📁 Head, Tail, Grep — The Deadly Trio of Linux Text Processing 🔥 (Bonus: sed sneak peek)

#linux #cli #devops #grep

Welcome back to another command-line deep dive, fellow terminal warriors ⚔️! Today, we’re slicing and dicing files using three legendary Linux commands:

head, tail, and grep — your data ninjas for filtering, scanning, and previewing files with surgical precision. 🧠🔍

And hey — there's a sneaky bonus at the end 👀 (sed makes a guest appearance). Let’s dig in!

🔹 head – The Top Gun 🛫

👉 Syntax: 

head [options] [file_name]
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📌 Default Behavior:

Shows the first 10 lines of a file.

🧪 Examples: 

head /etc/passwd
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Outputs the first 10 lines of the /etc/passwd file.

head -n 5 myfile.txt
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Shows first 5 lines. -n lets you define how many lines.

head -c 20 myfile.txt
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Prints the first 20 characters, not lines! ✂️

🔹 tail – The Underdog with Superpowers 🐕

👉 Syntax: 

tail [options] [file_name]
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📌 Default Behavior:

Shows the last 10 lines of a file.

🧪 Examples: 

tail /var/log/syslog
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See the last 10 lines of system logs — often where the juicy errors live 😈.

tail -n 3 notes.txt
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Just give me the last 3 lines, thanks.

tail -f /var/log/apache2/access.log
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Follow log output in real-time — this is ✨🔥 GOLD 🔥✨ when debugging live services. we will talk about this in the end.

🔹 grep – The Search King 👑

👉 Syntax: 

grep [options] pattern [file_name]
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📌 What it does:

Searches for patterns (strings/regex) in a file or input. It's your CLI Ctrl+F on steroids.

🧪 Examples: 

grep root /etc/passwd
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Show lines with the word root in /etc/passwd.

grep -i hello greetings.txt
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Case-insensitive search for hello (will match Hello, HELLO, etc.)

grep -v admin users.txt
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Show lines that don’t contain the word admin. -v = invert match.

ps aux | grep apache
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Find all processes with the name apache in them. Super useful when debugging services.

🔍 More Grep Options – Master the Match 💥

Let’s go beyond the basics and unlock the real power of grep.

🧪 Useful Options: 

grep -i pattern file.txt
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Ignore case (so Error, error, and ERROR are all matched).

grep -v pattern file.txt
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Invert match — show lines that do not contain the pattern.

grep -n pattern file.txt
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Show matched lines with line numbers.

grep -r pattern /path/to/dir
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Recursively search through all files and folders under the path — powerful for project-wide scans! 📁📂

grep -c pattern file.txt
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Count the number of matches (number of lines that contain the pattern).

grep -A 2 -B 2 "error" logfile.txt
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Show 2 lines after (-A) and 2 lines before (-B) each match — useful for contextual debugging.

grep -E 'foo|bar' file.txt
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Extended regex — match either foo or bar (acts like egrep).

🎯 Combine Powers – 🥷 Ninja Moves 

head -n 15 data.txt | grep "error"
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From the first 15 lines, only show those with error — quick scan!

tail -f /var/log/syslog | grep "disk"
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Watch for disk-related logs in real time — this is DevOps magic right here 🧙‍♂️.

🔸 Bonus: sed – The Silent Slicer 🍰

sed is like that cool silent ninja in the background — not flashy but lethal when used right.

🧪 Very Basic Example (line slicing): 

sed -n '5,10p' file.txt
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Print only lines 5 to 10 from the file. Think of this as a more surgical version of head | tail.

Want to delete lines? Replace text? sed's got you. But that's for another spicy article 🌶️.

✅ TL;DR Cheatsheet

Command Action
head -n 5 First 5 lines
tail -f Follow file in real-time
grep pattern Search lines with pattern
grep -v pattern Show lines without pattern
sed -n 'x,yp' Show only lines from x to y

🐾 Deep Dive into tail -f

The tail -f command isn’t just for reading — it’s for live monitoring.

✅ What it does:

  • Starts by printing the last 10 lines of a file.
  • Then, it keeps the file open and streams any new lines that are added.

Perfect for watching log files or real-time updates!

🧪 Examples: 

tail -f /var/log/syslog
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You'll see new logs appear as they’re written — ideal for monitoring services.

tail -f app.log | grep "ERROR"
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Only show real-time error logs. Great for live bug hunting 🔎💥

🧠 Pro Tip:

Use Ctrl + C to stop a tail -f process running in the terminal.

🚀 Final Thoughts

These three tools are the holy trinity of text processing in the Linux world 🧙‍♀️. Once you’re comfy with head, tail, and grep, you’re already way ahead of the pack.

💡 Pro Tip: Start combining these with awk, cut, and sed and you’ll become unstoppable in logs, data crunching, and automation.

🔔 Want a full post just on sed or awk next? Drop a comment and let me know 👇

Thanks for reading! 💻⚙️

Written by Sahil Sharma – aspiring DevOps ninja 🥷 | Linux fanatic 🐧 | Learning in public 🚀

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