You are probably wondering about that first line. The second (or third, if you count the empty line) should be clear, but that first one is new. It is called the shebang, but is sometimes also referred to as a sha-bang, hashbang, pound-bang, and/or hash-pling. Its function is pretty simple: it tells the system which binary to use to execute the script. It is always in the format of #!<binary path>. For our purposes, we will always use the #!/bin/bash shebang, but for Perl or Python scripts it would be #!/usr/bin/perl and #!/usr/bin/python3 respectively. It might seem unnecessary at first sight. We create the script named hello-world.sh, whereas a Perl or Python script would use hello-world.pl and hello-world.py. Why, then, do we need the shebang?

For Python, it allows us to easily distinguish between Python 2 and Python 3. You would normally expect people to switch to a newer version of a programming language as soon as it's there, but for Python this seems to require a lot more effort, which is why you see both Python 2 and Python 3 in use today.

Bash scripts do not end in .bash, but in .sh, the general acronym for shell. So, unless we specify the shebang for Bash, we will end up in a normal shell execution. While this is fine for some scripts (the hello-world.sh script would work fine), when we use the advanced functions of Bash, we will run into issues.