Sound Approach for Running a Shell Command?

[matt_the_hall]

This is my attempt at using the HEREDOC method:

import os

heredoc = """zulip-send --stream test --subject at_test --'message this is a test'END"""

os.system("at 8:55 <<END%s" % heredoc)
print "test"

The simpler version using the pwd command works fine, but with the above situation, 'at' yells at me about trying to use parameters that don't (for it) exist. Why would it be seeing --stream as a parameter for 'at' rather than as a parameter for 'zulip-send'?

import os

heredoc = """pwdEND"""

os.system("at 8:55 <<END%s" % heredoc)
print "test"