Question

I wonder if anyone has any insights into this. I have a bash script that should put my ssh key onto a remote machine. Adopted from here, the script reads,

#!/usr/bin/sh
REMOTEHOST=user@remote
KEY="$HOME/.ssh/id_rsa.pub"
KEYCODE=`cat $KEY`
ssh -q $REMOTEHOST "mkdir ~/.ssh 2>/dev/null; chmod 700 ~/.ssh; echo "$KEYCODE" >> ~/.ssh/authorized_keys; chmod 644 ~/.ssh/authorized_keys"

This works. The equivalent python script should be

#!/usr/bin/python
import os
os.system('ssh -q %(REMOTEHOST)s "mkdir ~/.ssh 2>/dev/null; chmod 700 ~/.ssh; echo "%(KEYCODE)s" >> ~/.ssh/authorized_keys; chmod 644 ~/.ssh/authorized_keys"' %
          {'REMOTEHOST':'user@remote',
           'KEYCODE':open(os.path.join(os.environ['HOME'],
                                       '.ssh/id_rsa.pub'),'r').read()})

But in this case, I get that

sh: line 1:  >> ~/.ssh/authorized_keys; chmod 644 ~/.ssh/authorized_keys: No
such file or directory

What am I doing wrong? I tried escaping the inner-most quotes but same error message… Thank you in advance for your responses.

Answer 1

You have a serious question — in that os.system isn’t behaving the way you expect it to — but also, you should seriously rethink the approach as a whole.

You’re launching a Python interpreter — but then, via os.system, telling that Python interpreter to launch a shell! os.system shouldn’t be used at all in modern Python (subprocess is a complete replacement)… but using any Python call which starts a shell instance is exceptionally silly in this kind of use case.

Now, in terms of the actual, immediate problem — look at how your quotation marks are nesting. You’ll see that the quote you’re starting before mkdir is being closed in the echo, allowing your command to be split in a spot you don’t intend.

The following fixes this immediate issue, but is still awful and evil (starts a subshell unnecessarily, doesn’t properly check output status, and should be converted to use subprocess.Popen()):

os.system('''ssh -q %(REMOTEHOST)s "mkdir ~/.ssh 2>/dev/null; chmod 700 ~/.ssh; echo '%(KEYCODE)s' >> ~/.ssh/authorized_keys; chmod 644 ~/.ssh/authorized_keys"''' % {
  'REMOTEHOST':'user@remote',
  'KEYCODE':open(os.path.join(os.environ['HOME'], '.ssh/id_rsa.pub'),'r').read()
})