Essential Bash Scripting: Basic Syntax and Examples for Beginners

Welcome to the world of Bash scripting! This powerful tool automates tasks, manages systems, and unlocks the full potential of your Linux/macOS terminal. Let’s break down core concepts with practical examples:

1. The Shebang Line

Always start scripts with this “magic line” to specify the interpreter:

#!/bin/bash

2. Variables

Declare variables and access them with $:

name="Alice"
echo "Hello, $name!"  # Output: Hello, Alice!

3. User Input

Use read for interactive scripts:

echo "What's your age?"
read age
echo "You're $age years old."

4. Conditionals (if Statements)

Compare values with -eq (equal), -lt (less than), etc.:

count=10
if [ $count -eq 10 ]; then
  echo "Count is 10"
elif [ $count -lt 5 ]; then
  echo "Too low"
else
  echo "Invalid"
fi

File Checks:

if [ -f "myfile.txt" ]; then
  echo "File exists"
fi

5. Loops

a) for Loop:

for fruit in apple banana cherry; do
  echo "I like $fruit"
done

b) while Loop:

counter=1
while [ $counter -le 3 ]; do
  echo "Count: $counter"
  ((counter++))
done

6. Command Arguments

Access arguments with $1, $2, etc.:

#!/bin/bash
echo "First argument: $1"
echo "All arguments: $@"

Run with: ./script.sh arg1 arg2

7. Exit Codes

Check success/failure of previous command with $?:

grep "search" file.txt
if [ $? -eq 0 ]; then
  echo "Text found!"
else
  echo "Text not found."
fi

8. Functions

Reusable code blocks with parameters:

greet() {
  echo "Hello, $1!"
}
greet "Bob"  # Output: Hello, Bob!

Practical Example: Backup Script

#!/bin/bash

# Backup directory creator
backup_dir="/tmp/backup_$(date +%Y%m%d)"
mkdir -p $backup_dir

# Copy files
cp -r ~/documents $backup_dir && \
echo "Backup completed in $backup_dir"

Running Your Script

1. Make it executable:
   chmod +x script.sh
2. Execute:
   ./script.sh

Key Tips:

• Case Sensitivity: VAR ≠ var
• Spacing: Use spaces in [ conditions ]
• Debugging: Add set -x at the start to trace execution
• Extensions: Use .sh (e.g., myscript.sh) for clarity

Master these fundamentals to automate file management, system monitoring, and complex workflows. Bash turns repetitive tasks into one-click solutions! Practice by modifying examples and explore advanced topics like arrays (${my_array[@]}) and regular expressions next. Happy scripting! 🐚