Bash Scripting

Bash scripting allows you to automate tasks by writing sequences of commands in a file (a script) and then executing that file. This is incredibly powerful for repetitive tasks, system administration, and creating custom tools.

Creating and Running a Bash Script

Create a new file: Use a text editor (like nano or vim) to create a new file. It’s common to use the .sh extension for shell scripts, but it’s not strictly required.
```
nano my_script.sh
```
Add the “shebang” line: At the very top of the file, add the following line:
```
#!/bin/bash
```
This line (called the “shebang”) tells the operating system which interpreter to use to execute the script (in this case, bash).

Write your script: Add the commands you want to execute, one per line.

#!/bin/bash
echo "Hello, world!"
echo "The current date is: $(date)"

Save the file: In nano, press Ctrl+O, then Enter, then Ctrl+X.
Make the script executable: Use the chmod command to give the script execute permissions:
```
chmod +x my_script.sh
```

Run the script: Execute the script using ./:

./my_script.sh

Sample Output:

Hello, world!
The current date is: Tue Oct 29 10:30:00 UTC 2024

Variables

Variables store data (text or numbers) that you can use in your script.

Assigning Values:
```
my_variable="Hello"
number=123
```
Note: There must be no spaces around the = sign.

Accessing Values: Use a $ before the variable name:

echo $my_variable
echo "The number is: $number"

User Input: Use the read command:

#!/bin/bash
echo "Enter your name:"
read user_name
echo "Hello, $user_name!"

Comments

Comments are lines that are ignored by the interpreter. They are used to explain your code.

# This is a single-line comment

# This is another comment.
# This script displays a greeting.
echo "Hello"  # This comment is at the end of a line