mailx does not work with subprocess

Question

I can send email by typing this command manually into the command line:

 echo "test email" | mailx -s "test email" someone@somewhere.net

I get the email in my inbox, works.

It does not work with subprocess though:

import subprocess
recipients = ['someone@somewhere.net']
args = [
    'echo', '"%s"' % 'test email', '|',
    'mailx',
    '-s', '"%s"' % 'test email',
] + recipients
LOG.info(' '.join(args))
subprocess.Popen(args=args, stdout=subprocess.PIPE).communicate()[0]

No errors, but I never receive the email in my inbox.

Any ideas?

score 1 · Accepted Answer · answered Nov 27 '14 at 18:33

The | character has to be interpreted by the shell, not by the program. What you currently do looks like the following command :

echo "test email" \| mailx -s "test email" someone@somewhere.net

That is do not have the shell process the | and pass it as a string to echo.

You have two ways to fix that :

explicitely start 2 commands from python with subprocess (echo and mailx) and pipe the output from echo to the input of mailx
use shell=True parameter in subprocess

The second solution is simpler and would result in :

import subprocess
recipients = 'someone@somewhere.net'
cmd = ('echo "%s" | mailx -s "%s"' % ('test email', 'test email')) + recipients
LOG.info(cmd)
subprocess.Popen(cmd, stdout=subprocess.PIPE, shell=True).communicate()[0]

But you should use full path in commands to avoid PATH environment problems that can result in security problems (you end in executing unwanted commands)

mailx does not work with subprocess

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