Command line Parameters in bash shell script in nested ssh

Question

I am trying to use $1, $2 variables which I have passed through command line to a bash shell script. These variables I am using within a ssh call. But its seems the variables within ssh are not getting replaced, the outer ones are getting replaced. Any workaround? Here's the code

#!/bin/bash

ssh -t "StrictHostKeyChecking=no" -i  $1 user@ip<<'EOF1'

ssh -t -i $1 user2@ip2 <<'EOF2'

exit
EOF2

exit
EOF1

Here the first $1 gets replaced but the second one doesn't. Its basically key name for password less authentication

If you want a better answer than what I've provided already, you'll need to ask a better question. Show code to reproduce the issue, perhaps? — Charles Duffy
– Charles Duffy, Commented May 16, 2016 at 20:02

Charles Duffy · Accepted Answer · 2016-05-16 20:39:24Z

6

Use printf %q to generate an eval-safe string version of your argument list:

# generate a string which evals to list of command-line parameters
printf -v cmd_str '%q ' "$@"

# pass that list of parameters on the remote shell's command line
ssh "$host" "bash -s $cmd_str" <<'EOF'
  echo "This is running on the remote host."
  echo "Got arguments:"
  printf '- %q\n' "$@"
EOF

For what you're really doing, the best practice is probably to use a ProxyCommand -- see the relevant documentation -- and to have your private key exposed via agent forwarding, rather than having it sitting on your bounce host on-disk. That said, it's straightforward enough to adopt the answer given above to fit the code in the question:

#!/bin/bash
printf -v args '%q ' "$@"
echo "Arguments on original host are:"
printf '- %q\n' "$@"
ssh -t "StrictHostKeyChecking=no" -i "$1" user@ip "bash -s $args" <<'EOF1'
  printf -v args '%q ' "$@" 
  echo "Arguments on ip1 are:"
  printf '- %q\n' "$@"
  ssh -t -i "$1" user2@ip2 "bash -s $args" <<'EOF2'
    echo "Arguments on ip2 are:"
    printf '- %q\n' "$@"
EOF2
EOF1

edited May 16, 2016 at 20:39

answered May 16, 2016 at 19:58

Charles Duffy

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2 Comments

Charles Duffy Over a year ago

@user3780835, ...expanded accordingly.

Oliver Blue Over a year ago

Thanks Charles for your time. I'd look into ProxyCommand as well.

chepner · Accepted Answer · 2016-05-17 11:44:07Z

1

Much simpler is to let ssh handle the tunneling for you.

ssh -o ProxyCommand="ssh user1@ip1 nc -w 10 %h %p" user2@ip2

(This example found at http://undeadly.org/cgi?action=article&sid=20070925181947).

edited May 17, 2016 at 11:44

answered May 16, 2016 at 20:44

chepner

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3 Comments

Charles Duffy Over a year ago

Definitely true -- being why I mentioned it in my answer [with a link to the OpenSSH Cookbook section on the subject] after the OP extended their question to make what they were doing clear. Being a bit more explicit -- as you're doing here -- doesn't hurt.

Oliver Blue Over a year ago

Hi charles/chepner, is it possible that the key for ip2 is on my main server and not on ip1? (The login to ip2 is possible via ip1 only though)

chepner Over a year ago

It should be, if you run an ssh-agent on your local machine and enable agent forwarding with the -A option (ssh -A -o ProxyCommand...).

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