5

I'm trying to test the ssh connection of a set of hosts using a corresponding set of test user accounts.

ie: testuser1 test ssh connection to server1, testuser2 test ssh connection to server2, testuser3 test ssh connection to server3 ect.

Each test user is logging in using a private key: ssh -i ~/keys/testuser1key testuser1@server1

However, I'm running into an issue when putting this information into a variable. Here is what I have for a script so far:

for host in $(cat hosts)
do
   if
      ssh -i $host 'true' exit
   then
      echo "SSH connection for $host ok"
   else
      echo "SSH connection for $host failed"
   fi
done
$SHELL

The host file looks like this:

~/keys/testuser1key testuser1@server1
~/keys/testuser2key testuser2@server2
~/keys/testuser3key testuser3@server3
...

I am getting errors such as could not resolve hostname true

I think the space in the host file are what's breaking the script. I've used a similar script no issue when running my user account and no "-i" ssh flag. (ssh myuseraccount@testserver1)

Any help or suggestions on a better way to do this is appreciated!

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2
  • Could you use Ansible instead of bash? Much easier with Ansible. Commented Jul 16, 2021 at 7:38
  • @AdamJRichardson this is good for learning bash Commented Jul 18, 2021 at 11:07

1 Answer 1

Reset to default
7

I'd suggest using a while read loop so that you can assign whitespace-separated tokens to individual variables, rather than relying on the implicit split+glob behavior of $(cat hosts)

The only tricky bit is that read reads from standard input by default - and so does ssh. So you either need to pass the -n flag to tell ssh to read from /dev/null:

while read -r identityfile host; do
  if ssh -n -i "$identityfile" "$host" true
  then
    echo "SSH connection for $host ok"
  else
    echo "SSH connection for $host failed"
  fi
done < hosts

or tell read to read from a different file descriptor:

while read -u3 -r identityfile host; do
  if ssh -i "$identityfile" "$host" true
  then
    echo "SSH connection for $host ok"
  else
    echo "SSH connection for $host failed"
  fi
done 3< hosts

Note: you've made things somewhat difficult by using ~ rather than $HOME for example to prefix the identity file portion of your hosts file. Quoting "$identityfile" prevents tilde expansion by the shell; however leaving it unquoted (as $identityfile) is dangerous because it permits word splitting and filename generation1. It seems that at least the OpenSSH implementation of ssh expands ~ itself, but if your ssh implementation doesn't, then extra processing would be required to handle it properly.

1 in this context it is filename generation (globbing) that is the primary concern, since if the name contains whitespace the whole approach is flawed.

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3
  • man ssh_config, "for user configurations, shell-like ‘~’ references to user home directories" Commented Jul 15, 2021 at 21:22
  • 1
    @roaima I was thinking of using "${identityfile/#~/$HOME}", but tbh I think I'd do something KISS like replacing < hosts with < <(sed 's/^~/$HOME/' hosts) Commented Jul 15, 2021 at 22:04
  • Even better (and I've learned today that you can anchor to start-of-string with # in a substitution too) Commented Jul 16, 2021 at 6:16

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