How to append to a file on remote server with pexpect

I'm trying to append public key to authorized keys file on a remote server with pexpect but it's not working. It seems that the redirection of output to file doesn't happen, although there are no errors. Here is my code:

print "DEGUG: ===  append to authorized keys  START ==="
print "DEBUG:  sending echo <local public key> >> /root/.ssh/authorized_keys"
print "        local public key: " + local_public_key
child.sendline('echo ' + local_public_key + ' >> /root/.ssh/authorized_keys')
child.expect(prompt)
child.expect(prompt)
child.sendline('echo $?')
child.expect(prompt)
ec = child.before.strip()
print("exit code: >>>>" + str(ec) + "<<<<")
print "DEGUG: ===  append to authorized keys  END ==="

Here is the output:

DEGUG: ===  append to authorized keys  START ===
DEBUG:  sending echo <local public key> >> /root/.ssh/authorized_keys
    local public key: ssh-rsa 
AAAAB3NzaC1yc2EAAAABIwAAAQEAy408yT80SP2x9rZkR56j4wsbpqUSYOW1uY8Lf4XfJLinbtcpwyyYGJCuNbA30ve1+Lt/AJ2d1VdSAS4Afu1LKucFmj2lN8dqKWsCUBYXXtkUHILVelRTglMGFLTbLJofXYwUXA60UWWilYvWJ2j4HRjHgxUP7i0fYy4ruy5zpspZ8Svr+PMY9UjA3HSnPhFB2ZHkC+9kzexfVCM7nvKw9LekxY0x/BrD5z6D+652sr8A9EOgBsg9A/soL4JMycdWmTBDe16O5f4Db5Qt7oqn3Hbw7lki1XULIvTzyNhUtoiGiQiCbCh7G1ba+IccvfrIaK+kpmugeoaTC4zldXEGbw==

echo ssh-rsa 
AAAAB3NzaC1yc2EAAAABIwAAAQEAy408yT80SP2x9rZkR56j4wsbpqUSYOW1uY8Lf4XfJLinbtcpwyyYGJCuNbA30ve1+Lt/AJ2d1VdSAS4Afu1LKucFmj2lN8dqKWsCUBYXXtkUHILVelRTglMGFLTbLJofXYwUXA60UWWilYvWJ2j4HRjHgxUP7i0fYy4ruy5zpspZ8Svr+PMY9UjA3HSnPhFB2ZHkC+9kzexfVCM7nvKw9LekxY0x/BrD5z6D+652sr8A9EOgBsg9A/soL4JMycdWmTBDe16O5f4Db5Qt7oqn3Hbw7lki1XULIvTzyNhUtoiGiQiCbCh7G1ba+IccvfrIaK+kpmugeoaTC4zldXEGbw==
 >> /root/.ssh/authorized_keys
R56j4wsbpqUSYOW1uY8Lf4XfJLinbtcpwyyYGJCuNbA30ve1+Lt/AJ2d1VdSAS4Afu1LKucFmj2lN8dqKWsCUBYXXtkUHILVelRTglMGFLTbLJofXYwUXA60UWWilYvWJ2j4HRjHgxUP7i0fYy4ruy5zpspZ8Svr+PMY9UjA3HSnPhFB2ZHkC+9kzexfVCM7nvKw9LekxY0x/BrD5z6D+652sr8A9EOgBsg9A/soL4JMycdWmTBDe16O5f4Db5Qt7oqn3Hbw7lki1XULIvTzyNhUtoiGiQiCbCh7G1ba+IccvfrIaK+kpmugeoaTC4zldXEGbw==
ssh-rsa 
AAAAB3NzaC1yc2EAAAABIwAAAQEAy408yT80SP2x9rZkR56j4wsbpqUSYOW1uY8Lf4XfJLinbtcpwyyYGJCuNbA30ve1+Lt/AJ2d1VdSAS4Afu1LKucFmj2lN8dqKWsCUBYXXtkUHILVelRTglMGFLTbLJofXYwUXA60UWWilYvWJ2j4HRjHgxUP7i0fYy4ruy5zpspZ8Svr+PMY9UjA3HSnPhFB2ZHkC+9kzexfVCM7nvKw9LekxY0x/BrD5z6D+652sr8A9EOgBsg9A/soL4JMycdWmTBDe16O5f4Db5Qt7oqn3Hbw7lki1XULIvTzyNhUtoiGiQiCbCh7G1ba+IccvfrIaK+kpmugeoaTC4zldXEGbw==
[root@slccaa01cn01 ~]#  >> /root/.ssh/authorized_keys
[root@slccaa01cn01 ~]# echo $?
echo $?
0
[root@slccaa01cn01 ~]# exit code: >>>>echo $?
0
[root@slccaa01cn01 ~]<<<<
DEGUG: ===  append to authorized keys  END ===

When I check authorized_keys file on remote, the new key is not added. It seems that the key is echoed to stdout instead of written to a file. Not sure how to resolve this.

Solution

Seems like you forgot to remove the trailing \n char in local_public_key. So try like this:

child.sendline('echo ' + local_public_key.strip() + ' >> /root/.ssh/authorized_keys')
#                                        ^^^^^^^^