Why we write #!/usr/bin/env python on the first line of a Python script?

The shebang line or hashbang line is recognized as the line #!/usr/bin/env python. This helps to point out the location of the interpreter intended for executing a script, especially in Unix-like operating systems. For example, Linux and macOS are Unix-like operating systems whose executable files normally start with a shebang followed by a path to an interpreter program that should execute a script.

• Shebang Line: This is the line that starts with #! (hashbang). It instructs the system on which interpreter to use to execute the script.
• /usr/bin/env: This is a standard Unix path to the env command responsible for finding and executing commands. Often it’s used in shebang lines so that it can find the specified interpreter.
• Python: This is the name of the interpreter we want to use. In this case, it's Python.

Why We Write #!/usr/bin/env Python On the First Line of a Python Script?

Below, are the reasons Why we write #!/usr/bin/env python on the first line of a Python Script.

• Specify the Interpreter: The purpose of a shebang line is to define which interpreter will execute a script. For this reason, python refers specifically to Python.
• Flexibility with /usr/bin/env: When /usr/bin/env is put before an interpreter command, it makes scripts more portable. It helps find Python regardless of its location in the filesystem precisely.

Example :

Let's consider a simple Python script named test.py

#!/usr/bin/env python
print("Hello, world!")

Hello, world!

The thing that happens when you run ./test.py in a Unix-like shell is as follows:

• On reading the shebang line #!/usr/bin/env Python, the operating system does so.
• It locates the Python command using /usr/bin/env.
• Then it runs the script using Python interpreter found at that location.

This method ensures that any user can execute this script regardless of where they have installed Python on their machine. Simply we can say that the shebang line #!/usr/bin/env python guarantees that the Python script will be executed with an appropriate interpreter, which in turn enables many development environment to use it.