What is the Usage of writing #!/usr/bin/env on the first line of a Python script? It is the first statement you write while writing the Python script. This line is called “shebang” or “hashbang”, it is used to tell the system which interpreter to use for running the script.
Many beginners might not know what it means and why it is used. In this article, we will see the importance and usage of this shebang with examples.
1. What is “#!/usr/bin/env” in the First Line of Python?
Write “#!/usr/bin/env” as the first line in the Python program/script that is used to tell the system which interpreter to use, this special line is called “shebang” or “hashbang”.
This first line sounds strange in the python script as this looks like a comment in python. Let’s take a look at the examples.
This is the code from the first file “file_1.py” without this special line.
# This is comment in the first line
print(‘hello world’)
This is the code from the second file “file_2.py” with special line.
#!/usr/bin/env python
# This is comment after the shebang
print(‘hello world’)
If you run these two files from the editor or terminal both will yield the same result. So what is the catch? Let me explain it to you.
The code in the first file file_1.py is what we normally do. To execute this program you have to run it like the below. It gives us the proper result. However, we can’t run this program from all operation system versions.
# Execute python script
python file_1.py
To write code for different users for distribution or for the different versions of python, we need to be clear. We have to tell the operating system what interpreter should our code be interpreted in.
The first line on the file_2.py is called the “shebang” or “hashbang” line, it is used to tell the system which interpreter to use for running the script. For example, a python script with this special line can be run with the below line.
# Execute the python script
./file_2.py
If you include the shebang line at the beginning of the script, you can run it directly from the command line by using the below command:
2. Running Scripts with Different Versions of Python
Let’s say you are having multiple versions of python installed on your system. You write the python code for a specific version of python. You will need to specify the python version each time during the execution otherwise you will get errors. This is where the main usage of !/usr/bin/env comes.
This means that it will make your script less portable, since the user running the script will need to know the path to the Python interpreter on their system. This can also lead to errors if you are using a virtual environment.
Let’s say your script is specifically designed to be run on python version 3.4 the first line of your python code should be like this:
#!/usr/bin/python3.4
# Your code Below
print(‘Hello World’)
This is specifically useful when you are using python version 3 and python version 2. For the code to be run on python version 3, you have to write it as follows:
#!/usr/bin/env python3
# Your code below
And for the default version of python, which in most systems is python version 2, you can write it like this.
#!/usr/bin/env python
# Your code Here
Remember, if the default version of python is 3, then it will run on that specific version.
3. Setting Script Execution Permissions
The shebang can also be used to set the execute permissions for a Python script. By including the shebang line at the beginning of the script and then using the chmod command to set the file permissions to the executable, you can run the script directly from the command line.
#!/usr/bin/env python
# Code Here
This shebang line is used in combination with the chmod command to set the file permissions to executable. For example, if your script is called app.py, you can run the following command to set the permissions and make the script executable:
chmod +x app.py
4. #!python vs #!/usr/bin/env
In many cases both #!python and #!/usr/bin/env python are used to specify the path to the Python interpreter that should be used to run a Python script.
Windows has a default behavior of using a default Python interpreter when no shebang is present. In this case, #!python could be used to explicitly specify the version of Python to use.
However, if you are running your script on a bash, then it is a good idea to use the #!/usr/bin/env instead of #!python.
5. Summary and Conclusion
In the article, you have learned what is the usage of writing #!/usr/bin/env on the first line of a Python script, we have seen the usage and importance of using #!python , #!/usr/bin/env and other alternatives of this shebang. I hope this article was helpful. If you have any questions, please leave them in the comment section.
Happy Coding!
What is the Usage of writing #!/usr/bin/env on the first line of a Python script? It is the first statement you write while writing the Python script. This line is called “shebang” or “hashbang”, it is used to tell the system which interpreter to use for running the script. Many beginners might not know what Read More Python, Python Tutorial, Python Environment