Creating Your First Shell Script and Understanding PATH

Let’s dive into hands-on Bash scripting by creating your very first script! This practical guide will walk you through the entire process from creation to execution, plus the crucial concept of the PATH variable.

Setting Up Your Workspace

Creating a Scripts Directory

First, create a dedicated directory for your scripts in your home directory:

mkdir ~/scripts

Alternative naming: Many users prefer ~/bin for their personal scripts, which is also a common convention.

Navigate to Your Scripts Directory

cd ~/scripts

Creating Your First Script

Using a Text Editor

Create your script file using any text editor (vim, nano, gedit, etc.):

vim first_script.sh

Important Notes on Filenames:

Avoid spaces in filenames - use underscores instead
Extension convention: .sh extension is common but optional
Linux tradition: Extensions aren’t strictly necessary for executables

Writing the Script Content

Enter these commands exactly as you would type them in the terminal:

#!/bin/bash

# Create a new directory
mkdir -p drun

# Create a file with content
echo "hello bash world" > drun/file.txt

# List current directory contents
ls -la .

# Display the file contents
cat drun/file.txt

Explanation:

mkdir -p drun: Creates directory drun (with -p to avoid errors if it exists)
echo "hello bash world" > drun/file.txt: Writes text to a file
ls -la .: Lists current directory details
cat drun/file.txt: Displays file contents

Making Your Script Executable

Before you can run your script, you need to give it execute permissions:

Option 1: Owner Only (Recommended for personal scripts)

chmod 700 first_script.sh

Option 2: All Users

chmod +x first_script.sh

Running Your Script

Method 1: Using Relative Path (Current Directory)

./first_script.sh

The ./ tells the shell to look in the current directory.

Method 2: Using Absolute Path (From Any Directory)

/home/student/scripts/first_script.sh

Method 3: Just the Script Name (After PATH Configuration)

Once you configure your PATH (explained below), you can simply run:

first_script.sh

Understanding the PATH Variable

What is PATH?

The PATH variable is an environment variable that tells the shell where to look for executable files. When you type a command, the shell searches through directories listed in PATH in order.

Viewing Your Current PATH

echo $PATH

You’ll see something like:

/usr/local/bin:/usr/bin:/bin:/usr/local/games:/usr/games

Why Running Just the Script Name Fails Initially

When you type first_script.sh, the shell searches for it in the PATH directories. Since your ~/scripts directory isn’t in PATH, you get “command not found.”

Adding Your Scripts Directory to PATH

Temporary Addition (Current Session Only)

export PATH=$PATH:~/scripts

Permanent Addition (Persists After Reboot)

Open your .bashrc file:
```
nano ~/.bashrc
```
Add this line at the end:
```
export PATH="$PATH:~/scripts"
```
Save and exit (Ctrl+X, then Y, then Enter in nano)
Reload the configuration:
```
source ~/.bashrc
```
Or simply open a new terminal.

Verify the Change

echo $PATH

You should now see ~/scripts at the end of the PATH.

Important Security Consideration

PATH Order Matters

The shell searches directories in the order they appear in PATH. If you have a script named ls in your scripts directory, it won’t override the system’s ls command because /bin appears before ~/scripts in the PATH.

Best Practice: Avoid naming your scripts the same as common system commands to prevent confusion.

Troubleshooting Common Issues

”Command Not Found” Errors

Check if script is executable: ls -la first_script.sh
Verify PATH includes script directory: echo $PATH
Reload .bashrc: source ~/.bashrc

Permission Denied

Add execute permission: chmod +x first_script.sh

Script Runs But Commands Fail

Check command syntax: Ensure commands work when typed directly in terminal
Verify file paths: Use absolute paths or relative paths correctly

Key Takeaways

Scripts are just text files containing commands you’d normally type
Permissions are required: Scripts need execute permission (chmod +x)
PATH determines accessibility: The shell only finds commands in PATH directories
Two execution methods: Relative path (./script.sh) or absolute path (/full/path/script.sh)
PATH modifications: Can be temporary (current session) or permanent (via .bashrc)
Security matters: Be mindful of PATH order and script naming

Next Steps

Now that you’ve created your first script, you can:

Add more complex logic (conditionals, loops, functions)
Create aliases for your most-used scripts
Schedule scripts to run automatically with cron
Share scripts with other users

Your journey into Bash automation has officially begun!