Bash

🧠 The Developer’s Command Line: Mastering Linux BASH for Network Automation

A complete technical overview of BASH for learners, interviewers, and automation engineers.

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📌 Why BASH Matters in Network Automation

For modern network engineers working with Python, understanding the Linux BASH shell is just as crucial. BASH serves as the interface between the user and the operating system, offering:

• Powerful scripting capabilities
• Efficient environment navigation
• Critical tools for automation and deployment

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🔍 Understanding the BASH Shell

• BASH stands for Bourne Again SHell
• Default shell on most Linux distros since 1989
• Lightweight and powerful compared to a full GUI
• Supports: piping, conditionals, variables, loops

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📚 Core BASH Concepts

📄 Accessing Built-in Documentation

• man <command> – View manual pages for any command
  Example: man ls

🔐 Running Commands with Elevated Privileges

• sudo <command> – Run as superuser
  Example: sudo apt update

🔗 Command Chaining with Pipes

• command1 | command2 – Pipe output of one command into another
  Example: cat file.txt | more

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📁 Navigating the Linux File System

Command	Description
cd	Change directory. cd / (root), cd .. (up), cd ~ (home)
pwd	Print working directory
ls	List directory contents
ls -a	Show all files (including hidden)
ls -l	Long listing with permissions, owners
mkdir <dir>	Create new directory

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📂 File Management Commands

Command	Description
cp <src> <dest>	Copy files or directories. Use -r for folders
mv <src> <dest>	Move or rename files/folders
rm <file>	Remove file. Use -rf to force delete directories
touch <file>	Create empty file or update timestamps
cat <file>	Show file content or pipe to another command

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🌍 Managing Environment Variables

🔎 Viewing Environment Variables

• env – List all environment variables
• env | more – View with pagination

💡 Checking a Specific Variable

• echo $VARIABLE
  Example: echo $PATH

🛠️ Updating a Variable (Temporary)

• export VAR=value
  Example: export PATH=$PATH:/custom/bin

♻️ Making Permanent Changes

• Edit .bashrc or .zshrc
• Add: export PATH=$PATH:/custom/bin
• Reload: source ~/.bashrc or . ~/.bashrc

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🧰 Why Mastering BASH Matters

Mastering BASH enables:

• Efficient file and system management
• Writing automation scripts
• Better debugging and deployment of Python code
• Meeting certification requirements (e.g., Cisco DEVASC 200-901)

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📌 Summary for Revision

• Know how to navigate and manipulate the Linux file system
• Master file operations: copy, move, delete, create
• Learn pipes, redirection, variables, and permissions
• Understand user roles and sudo access
• Be able to modify environment variables (temporarily and permanently)

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🧠 Keep this BASH cheat sheet close as your quick-reference guide in interviews, labs, or while working on network automation scripts.

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