Shell

Introduction to the Shell Utilities

Cement includes a Shell Utility Module with helpers for common tasks related to executing commands, spawning subprocesses/threads, and other tasks.

API References:

• Cement Shell Utility Module

Prompting User Input

Requesting input from the user is straight forward, however we've included the shell.Prompt utility to expand beyond just a simple one-dimensional input response.

Example: User Input Prompts

example.py

from cement import shell

### simple user response prompt

p = shell.Prompt("Press Enter To Continue", default='ENTER')
res = p.prompt()

### provide a numbered list for longer selections

p = shell.Prompt("Where do you live?",
                 options=[
                     'San Antonio, TX',
                     'Austin, TX',
                     'Dallas, TX',
                     'Houston, TX',
                 ],
                 numbered = True)
res = p.prompt()

### Create a more complex prompt, and process the input

class MyPrompt(shell.Prompt):
    class Meta:
        text = "Do you agree to the terms?"
        options = ['Yes', 'no', 'maybe-so']
        options_separator = '|'
        default = 'no'
        clear = True
        max_attempts = 99

    def process_input(self):
        if self.input.lower() == 'yes':
            # do something crazy
            pass
        else:
            # don't do anything... maybe exit?
            print("User doesn't agree! I'm outa here")

p = MyPrompt()

cli

$ python example.py

### simple user response prompt

Press Enter To Continue

### provide a numbered list for longer selections

Where do you live?

1: San Antonio, TX
2: Austin, TX
3: Dallas, TX
4: Houston, TX

Enter the number for your selection: 1

### Create a more complex prompt, and process the input

Do you agree to the terms? [Yes|no|maybe-so] no
User doesn't agree! I'm outa here

Executing Commands

Shell commands can be executed via the shell.cmd() function in two ways; by capturing STDOUT/STDERR and exit code, or just the exit code and letting STDOUT/STDERR print to console normally.

Example: Executing Commands

from cement import shell

### execute command and capture output
out, err, code = shell.cmd('echo helloworld')

### execute command with output to console
code = shell.cmd('echo helloworld', capture=False)

Spawning Processes and Threads

Spawning processes and threads is easy via the shell.spawn() helper.

Example: Spawning Processes and Threads

from cement import shell

def add(a, b):
    print(a + b)

### spawn a process
p = shell.spawn(add, args=(12, 27))
p.join()

### spawn a thread
t = shell.spawn(add, args=(12, 27), thread=True)
t.join()

See the multiprocessing and threading modules in the Python standard library for more information on working with processes and threads.