I have a bash script like:
#!/bin/bash echo Hello world!
How do I execute this in Terminal?
Firstly you have to make it executable using: chmod +x name_of_your_file_script.
chmod +x name_of_your_file_script
After you made it executable, you can run it using ./same_name_of_your_file_script
./same_name_of_your_file_script