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Carnifex provides an api for executing commands. The processes can be started locally or remotely on another machine with minimal effort for the user.

The Process Inductor

The process inductor classes abstract execution of processes. It lets you induce processes via run, getOutput, getExitCode and the slightly more complex method execute processes.

  • Inductor.run: execute and a command and run the process until completed (or terminated), then return stdout, stderr and exit code of the process
  • Inductor.getOutput: just like run, but only gather output (stdout and/or stderr can be specified)
  • Inductor.getExitCode: like the other two, but only return the exit code of the process
  • Inductor.execute: execute the command and let you bind a Twisted ProcessProtocol to the process to further control how the process is run. You can have the ProcessProtocol interact with the file descriptors of the process and send signals to terminate it.

All of these ways of running processes can be used in the same way both for starting a local sub process, or a remote process on another machine.

Local processes

import carnifex
from twisted.internet import reactor
inductor = carnifex.LocalProcessInductor(reactor)

Remote processes

import carnifex
from twisted.internet import reactor
inductor = carnifex.SSHProcessInductor(reactor, 'localhost', 22)

Building commands

To start a process with carnifex, you need to supply at least one parameter, which is the executable to launch. This is the bare minimum, and does not give you any flexibility to specify arguments to the executable. To do that, you'll need to specify one more argument args, which basically is the argument list that is passed to the process. The argument list consist of the name of the process and subsequent arguments to it. The name is usually the same as the executable

One usual use case is the following

args = ['echo', 'hello world']
inductor.run(args[0], args)

This can be a quite tedious way of specifying the command line to run, so we have the convenience method parseCommandLine to assist us. parseCommandLine will take a command line string - like you would type it in a shell - and parse it to a dictionary, suitable for the keyword arguments to the inductor methods.

Here is a more complex example, to illustrate the usefulness of the parseCommandLine function:

complex_command_line = """\
python -c
"import sys
sys.stdout.write('hello stdout\\n')
sys.stderr.write('whops, we err\\'d'\\n)
exit(1)
"
"""
exec_args = parseCommandLine(complex_command_line)
inductor.run(**exec_args)

Which will launch a python process that outputs hello stdout on standard output, whops, we err'd on standard error, and exits with exitcode 1

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