perl one liner inside python script

Question

I have a perl one liner that appends a string at the end of a particular line and it works when I run the one liner on the host. For instance, I'm looking to append 'boy857sr xxxxxxx' at the end of a line that starts with 'AllowUsers'

perl -pi.bak -e 's/^(AllowUsers.*)/\1 boy857sr xxxxxxx/g;' /etc/ssh/sshd_config

Works perfectly!

AllowUsers boy857bt soladmin svc-Orion_SAM solarw boy857lj boy806nk boy806sk   boy857sr xxxxxxx

But when I run it inside a python script, it wipes out the 'AllowUsers' line and add another line, look below:

#RSAAuthentication yes
^A kn857sr xxxxxxx

Here is the python script.

import pxssh

my_list=[
"server121"
]


for i in my_list:
    s = pxssh.pxssh(timeout=15, maxread=2000000)
    s.SSH_OPTS += "-o StrictHostKeyChecking=no"
    s.SSH_OPTS += "-o UserKnownHostsFile=/dev/null"
    s.login(i,'username','password')
    print (i)

    s.sendline('/usr/local/bin/sudo su -')
    s.expect('Password: ')
    s.sendline('xxxxxxx')

    s.prompt()
    print s.before
    s.sendline('perl -pi.bak -e \'s/^(AllowUsers.*)/\1 boy857sr xxxxxxx/g;\' 
/etc/ssh/sshd_config')
    s.prompt()
    print s.before

    s.sendline('exit')
    s.logout()

Answer 1

Python interprets the \1 in your replacement string as the character 0x01 (which often renders as ^A).

Moreover, using \1, \2 etc. in Perl regexes is reserved to the left hand side of the s/// operator, i.e. to the pattern. On the right hand side (the replacement string) you should use $1, $2 etc. instead.

From the docs

... It is at this step that \1 is begrudgingly converted to $1 in the replacement text of s///, in order to correct the incorrigible sed hackers who haven't picked up the saner idiom yet. A warning is emitted if the use warnings pragma or the -w command-line flag (that is, the $^W variable) was set.

So:

s.sendline('perl -pi.bak -e \'s/^(AllowUsers.*)/$1 boy857sr xxxxxxx/g;\' /etc/ssh/sshd_config')

should do the trick.

---

Update: Eventually I found the reference page for \1 vs. $1 (thanks to this post).