Building Command Line Applications using the click-shell Library

The click-shell is a Python library that’s built on top of the standard cmd library. It is an extension of the click library that’s used for building command-line applications. These command-line applications are programs that use a command-line interface(CLI) for receiving commands from users. These commands are in the form of text, and they are for instructing the computer to do a specific task. One thing that’s notable about command-line applications is that they do not have a graphical user interface(GUI), it’s just the console with some background and the user is prompted to enter commands. Have you ever wondered how a popular command line application like Git works? if you are curious and want to know how it works and you fancy the idea of building your own command line application then this tutorial is for you.

These is what we will cover:

• Installing the click-shell Library
• Creating the Shell
• Adding a Command to the Shell
• Getting Advanced
• Conclusion

Installing the click-shell Library

To use the click-shell library you need to install it on your machine, enter this command in your terminal:
$ pip install click-shell

Creating the Shell

Now that we have installed click-shell, let us create a new Python file and call it automation_shell.py. Make it look like this:

from click_shell import shell

message = """
Welcome to Ninja Shell!!!Please enter a command below.
"""
# creating the shell
@shell(prompt='ninjashell/>', intro=message)
def my_shell():
    pass

# executing the shell 
if __name__ == '__main__':
    my_shell()

In the code, we are importing the shell from click_shell, then we are creating a string that will be the shell’s welcoming message.

To create the shell, use the @shell() decorator which takes prompt and intro as arguments, both these arguments are strings.

After the shell’s definition, create its function with a pass statement inside, and finally, we are executing the function inside the if block.

Adding a Command to the Shell

Let’s add the first command to the shell, this command will just print a hello word text. To do that, below the shell paste this code:

# adding a command to print hello world message
@my_shell.command() # adds a shell’s command
def hello_world():
    print("Hello World!")

To add a command to the shell, use the command() method. Create the command which is a Python function, then inside this function define what you want the command to do when executed. Note, the command that we will enter is the hello-world.

To run the program, use:
$ python automation_shell.py

Make sure you get this output:

Enter the hello-world command and the output will be this:

The click-shell library handles so much under the hood, like exception handling and keeping the shell running even when an error occurs and it has some inbuilt commands like the exit command.

Try to enter a command that does not exist, you will get this:

And to break out of the shell, just enter the exit command.

Getting Advanced

We will now modify the shell to do meaningful tasks like listing the available shell commands, printing the current date and time, and creating a file. Open the file and replace the current code with this code:

from click_shell import shell
from datetime import datetime

message = """
Welcome to Ninja Shell!!!Please enter a command below. If you want to
see a list of all the available commands, enter "help".
"""

# creating the shell
@shell(prompt='ninjashell/>', intro=message)
def my_shell():
    pass

# adding command to the shell to list available commands
@my_shell.command()
def help(): # the command will be help
    print(
        """Here is a list of all commands:
*******************************
help: List all the available commands
date-time: Prints current date and time
create-file: Creates a new file and write to it
exit: Exits the shell
        """
        )

@my_shell.command()
def date_time(): # the command will be date-time
    now = datetime.now().strftime("%d/%m/%Y %H:%M:%S") # getting the formatted current date and time
    print(f"The current date&time is: {now}")

@my_shell.command()
def create_file(): # the command will be create-file
    filename = input("Enter the file name and extension:") # getting the filename from user
    content = input("Enter the file content:") # getting the file contents from user
    # creating the new file, opening it in write mode
    with open(filename, "w") as f:
        f.write(content) # writing content to the file

# executing the shell 
if __name__ == '__main__':
    my_shell()

To be on the same page, let’s do some code breakdown. This code is not different from the previous code, here we have a few additions.

We have imported the datetime library, extended the message string, and added 3 commands, help, date-time, and create-file.

The help command will list all the available commands for the shell, the date-time command will print the current date and time and lastly, the create-file command will assist the user in creating a basic file.

Run the program and enter the help command to get this output:

If you enter the date-time command, you get this:

To create a file, enter the create-file command:

You will find the file in your current working directory:

With this content:

Conclusion

That’s it, geeks!!! I hope you have learned so much from this piece. Remember there is so much that you could do with click-shell. I have only shown you a few things you could do with the library in this piece. But you can go the extra mile by building advanced commandline applications. Thanks for reading!!!! and do let me know in the comment section how you have benefitted from this piece.