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stable/3.0

Cement Developer Guide

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
cli
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()
$ 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.

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Outline

Introduction to the Shell Utilities

Prompting User Input

Executing Commands

Spawning Processes and Threads