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:

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: 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
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
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.