🧠 Linux Redirection & Pipes: The Magic of `>`, `>>`, `|`, and File Descriptors 🎯

Ever wondered how Linux commands talk to each other? Let's dive into the power-packed symbols and streams that drive automation in the terminal.

From STDOUT to 2>&1, this is your one-stop cheat sheet 🧾

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🎬 What Are STDIN, STDOUT & STDERR?

Every process in Linux interacts with 3 default streams:

Stream	Meaning	File Descriptor	Role
STDIN	Standard Input	0	Takes input (usually keyboard)
STDOUT	Standard Output	1	Shows successful command output
STDERR	Standard Error Output	2	Displays error messages

➡️ STDOUT is for successful output, while STDERR is where errors are sent — they are separate!

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🔢 What’s a File Descriptor?

File Descriptors are just numbers assigned to files or streams opened by a process.

They help the shell identify where to read/write.

Standard mapping:

0 - STDIN   (input)
1 - STDOUT  (normal output)
2 - STDERR  (error output)

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🔧 Shell Symbols Cheat Sheet

Symbol	Name	What It Does
;	Command Separator	Runs commands one after another, regardless of success.
|	Pipe	Sends output of one command to input of another.
>	Redirect Output	Sends STDOUT to a file (overwrite).
>>	Redirect Output	Sends STDOUT to a file (append).
2>	Redirect STDERR	Sends errors to a file.
2>&1	Merge Outputs	Merges STDERR into STDOUT.

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🚀 Real-Life Examples

🟩 ; — Run Multiple Commands

echo "Start"; ls; echo "End"

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🟦 | — Pipe Output into Another Command

ps aux | grep apache

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🟥 > — Redirect STDOUT (Overwrite)

echo "Hello World" > file.txt

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🟨 >> — Redirect STDOUT (Append)

echo "New Line" >> file.txt

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🟧 2> — Redirect STDERR

ls notafile 2> error.log

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🟪 2>&1 — Combine STDOUT + STDERR

make > output.log 2>&1

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🧠 Bonus: Redirect STDIN (Input)

sort < names.txt

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💡 Quick Reference Table

Operator	Meaning	Example
>	STDOUT to file (overwrite)	echo hi > file.txt
>>	STDOUT to file (append)	echo again >> file.txt
2>	STDERR to file	cmd 2> errors.txt
&>	STDOUT + STDERR to file	cmd &> alloutput.txt (Bash only)
2>&1	Merge STDERR to STDOUT	cmd > out.txt 2>&1
<	Redirect file as input	sort < names.txt
;	Run commands in sequence	date; cal

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🔥 Bash Scripting Overview

These redirection symbols and streams are heavily used in bash scripting to handle outputs, store logs, and avoid error clutter. For example:

#!/bin/bash
ls /etc > out.txt 2> err.txt

In upcoming posts, we’ll dive deeper into bash scripting, but this gives you a quick taste of what’s possible 🔧.

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📌 Coming Soon: Quotes in Shell Scripts

We’ll soon talk about the differences between single quotes '...', double quotes "...", and backticks ...\ — and how they change how commands behave in shell scripting.

Stay tuned for the next post! 📚

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🏁 Wrap-Up

These symbols may look tiny, but they are mighty! Mastering them helps you script smarter, debug easier, and automate faster.

💬 Got a trick or shortcut you love? Share it in the comments!

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#Linux #Bash #ShellScripting #CommandLine #DevOps #Redirection #CheatSheet