Shebang and Interpreter Directive

In a Unix-like system, shebang precedes the interpreter directive which specifies the interpreter program to be run. The following examples are based on Python 3, including the Anaconda 3 interpreter. If the Anaconda3 Python interpreter is installed, when the user enters:

which python3

The terminal emulator returns:

/root/anaconda3/bin/python3

The example above helps the user hard code a local interpreter directive, which is less flexible than a global directory path. At the very first line of the script file, simply add a Unix shebang before appending the path:

#!/root/anaconda3/bin/python3

env Shell Command

The following demonstrates a more flexible global example:

#!/usr/bin/env python3

One purpose of the env shell command is to execute a program in a modified environment. In this case, python3. env searches the PATH environmental variable for Python’s directory path in a Unix-like operating system—OS X, Linux, etc.

Unix Dot Slash

As an example, in a unix-like terminal emulator, if the Python script is based on Python 3.5, and the interpreter directive is:

#!/usr/bin/python3.5

Then the following will allow that shell script to self execute in MacOS or Linux:

./foo.py

To self execute a shell script, the user will likely need to configure executable permission, e.g. chmod a+x foo.py. Also, the ./ prefix specifies current directory.

Your Turn

In the terminal emulator of a Unix-like system, try entering:

which python2