1. Core Purpose & Concepts

• Core Purpose: To write a series of Linux commands that need to be executed in order into a text file, creating a “script”. By running this single script file, a multi-step task can be automated without manually entering each command.
• Core Terminology:
• Bash Script: A plain text file containing a series of Linux commands. The <span>.sh</span> extension is a conventional naming method to help humans recognize it, but it is not required by the system.
• Interpreter: A program that can read and execute the commands in the script file. For Bash scripts, the interpreter is the Bash Shell itself.
• Shebang (<span>#!</span>):Must be located on the first line of the script file, starting with a special sequence of <span>#!</span>. It tells the operating system which interpreter to use to execute this file. For Bash scripts, it is always <span>#!/bin/bash</span>.
• Executable Permission: A permission attribute of a file that marks it as runnable as a program. This permission must be granted using the <span>chmod +x</span> command.
• <span>$PATH</span> Environment Variable: A list of directory paths where all executable programs are located. When you enter a command in the terminal, the Shell looks for the corresponding program in the directories listed in this variable.
• <span>~/.bashrc</span>: An important configuration file for the Bash Shell. Commands in this file are executed every time a new terminal is opened. It is the best place to modify the <span>$PATH</span> variable.
• <span>~/bin</span> Directory: A conventional directory under the user’s home directory, specifically for storing the user’s own executable scripts. By adding this directory to <span>$PATH</span>, scripts stored here can be called directly by name like system commands from any path.

2. Key Steps & Commands

To create a script that can be run anytime and anywhere, the following steps are usually followed:

Step 1: Create and Write the Script

1. Create File: Use <span>nano</span> or another text editor to create a new file.

   Bash

   nano my_backup.sh

• ounter(line

#!/bin/bash

• ounter(line

# This is an example script for creating backups# tar -czf ~/Desktop/my_backup.tar.gz ~/Documents ~/Pictures

• ounter(line
• ounter(line

Step 2: Grant Execute Permission

To allow the script to be run directly, rather than only through <span>bash my_script.sh</span>, it must be granted execute permission.

Bash

chmod +x my_backup.sh

Step 3: Make the Script Globally Available (Recommended)

1. Create <span>bin</span> Directory: Create a <span>bin</span> directory in your home directory (if it does not already exist).

   Bash

   mkdir -p ~/bin

• ounter(line

mv my_backup.sh ~/bin/my_backup

• ounter(line

# Open the configuration file with nano
ano ~/.bashrc
# Add the following line at the endexport PATH="$HOME/bin:$PATH"

Script vs. Alias

3. Practical Use Cases

• Automated Backup: Create a script that uses the <span>tar</span> command to periodically package and compress important directories (like <span>~/Documents</span>, <span>~/Pictures</span>) into a backup file.
• Project Initialization: Write a script to create a standard directory structure for a new project (like <span>src</span>, <span>dist</span>, <span>tests</span>) with commands like <span>git init</span> executed for initialization.
• System Status Report: Create a script that automatically collects system information (like disk space <span>df</span>, memory usage <span>free</span>) and outputs the report to a log file.

4. Common Pitfalls

• Forgetting or Miswriting Shebang: If there is no <span>#!/bin/bash</span>, or it is not on the first line, the system may not know which interpreter to use when running the script directly with <span>./script.sh</span>, leading to failure.
• Forgetting to Grant Execute Permission:<span>chmod +x</span> is a very easy step to forget but is crucial. If forgotten, trying to run with <span>./script.sh</span> will prompt “Permission denied”.
• <span>$PATH</span> Not Taking Effect Immediately: After modifying the <span>.bashrc</span> file, you must restart the terminal session for the new <span>$PATH</span> variable to take effect. It will not be effective in the current terminal.
• Permission Issues in Scripts: Scripts are executed with the identity of the user running them. If a command in the script requires administrative privileges (for example, modifying files in the <span>/etc</span> directory), the script must be run with <span>sudo ./my_script.sh</span>, otherwise that command will fail.