How to use os.spawnv to send email copy using Python?
Question: First let me say that I know it's better to use the subprocess module, but I'm
editing other people's code and I'm trying to make as few changes as possible,
which includes avoiding the importing any new modules. So I'd like to stick to
the currently-imported modules (os, sys, and paths) if at all possible.

The code is currently (in a file called postfix-to-mailman.py that some of you
may be familiar with):

    
    
    if local in ('postmaster', 'abuse', 'mailer-daemon'):
      os.execv("/usr/sbin/sendmail", ("/usr/sbin/sendmail", 'first@place.com'))
      sys.exit(0)
    

This works fine (though I think sys.exit(0) might be never be called and thus
be unnecessary).

I believe this replaces the current process with a call to /usr/sbin/sendmail
passing it the arguments /usr/sbin/sendmail (for argv[0] i.e. itself) and
'someaddress@someplace.com', then passes the environment of the current
process - including the email message in sys.stdin - to the child process.

What I'd like to do is essentially send another copy of the message before
doing this. I can't use execv again because then execution will stop. So I've
tried the following:

    
    
    if local in ('postmaster', 'abuse', 'mailer-daemon'):
      os.spawnv(os.P_WAIT, "/usr/sbin/sendmail", ("/usr/sbin/sendmail", 'other@place.com'))
      os.execv("/usr/sbin/sendmail", ("/usr/sbin/sendmail", 'first@place.com'))
      sys.exit(0)
    

However, while it sends the message to other@place.com, it never sends it to
first@place.com

This surprised me because I thought using spawn would start a child process
and then continue execution in the current process when it returns (or without
waiting, if P_NOWAIT is used).

Incidentally, I tried os.P_NOWAIT first, but the message I got at
other@place.com was empty, so at least when I used P_WAIT the message came
through intact. But it still never got sent to first@place.com which is a
problem.

I'd rather not use os.system if I can avoid it because I'd rather not go out
to a shell environment if it can be avoided (security issues, possible
performance? I admit I'm being paranoid here, but if I can avoid os.system I'd
still like to).

The only thing I can think of is that the call to os.spawnv is somehow
consuming/emptying the contents of sys.stdin, but that doesn't really make
sense either. Ideas?


Answer: While it might not make sense, that does appear to be the case

    
    
    import os
    
    os.spawnv(os.P_WAIT,"/usr/bin/wc", ("/usr/bin/wc",))
    os.execv("/usr/bin/wc", ("/usr/bin/wc",))
    
    $ cat j.py | python j.py 
           4       6     106
           0       0       0
    

In which case you might do something like this

    
    
    import os
    import sys
    
    buf = sys.stdin.read()
    wc = os.popen("usr/sbin/sendmail other@place.com","w")
    wc.write(buf)
    wc.close()
    wc = os.popen("usr/sbin/sendmail first@place.com","w")
    wc.write(buf)
    wc.close()
    sys.exit(0)
    

