Introduction to Bash Scripting

Bash (Bourne Again SHell) is a command-line interface and scripting language used in Unix and Unix-like operating systems, including Linux and macOS. Bash scripts are text files containing a series of commands that can be executed by the Bash shell.

1. Creating a Bash Script

To create a Bash script:

Open a text editor
Start the file with a shebang: #!/bin/bash # This line tells the shell what to use as the interpreter. Can be bash, python, etc...
Add your commands
Save the file with a .sh extension (e.g., myscript.sh)
Make the script executable: chmod +x myscript.sh

Here's a simple example:

#!/bin/bash
echo "Hello, World!"

2. Variables

Variables in Bash are created by assigning a value:

name="John"
age=30
echo "Name: $name, Age: $age"

Use $ to reference variables. For command substitution, use $(command):

current_date=$(date +%Y-%m-%d)
echo "Today is $current_date"

Output: Today is 2024-09-07

3. User Input

Use read to get user input:

echo "What's your name?"
read user_name
echo "Hello, $user_name!"

4. Conditional Statements

If-else statements:

if [ "$age" -ge 18 ]; then
    echo "You are an adult"
else
    echo "You are a minor"
fi

Note the spaces around the brackets and comparison operator.

5. Loops

For loop:

for i in {1..5}
do
echo "Iteration $i"
done

While loop:

counter=1
while [ $counter -le 5 ]
do
echo "Counter: $counter"
((counter++))
done

6. Functions

Define and call functions:

greet() {
    echo "Hello, $1!" # $1 takes the first argument passed after the function
}

greet "Alice"
greet "Bob"

7. Command-line Arguments

Access command-line arguments using $1, $2, etc.:

echo "Script name: $0"
echo "First argument: $1"
echo "Second argument: $2"
echo "All arguments: $@"

8. File Operations

Check if a file exists:

if [ -f "myfile.txt" ]; then
echo "myfile.txt exists"
else
echo "myfile.txt does not exist"
fi

Read from a file:

while IFS= read -r line
do
echo "$line"
done < "myfile.txt"

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