How to run a script after connected with ssh

Question

I've heard multiple answers of rights and wrongs and I still don't know if its possible. I ssh to a server then want to run a block of script.

while read server <&3; do   #read server names into the while loop    
serverName=$(uname -n)
 if [[ ! $server =~ [^[:space:]] ]] ; then  #empty line exception
    continue
 fi   
 echo server on list = "$server"
 echo server signed on = "$serverName"
 if [ $serverName == $server ] ; then #makes sure a server doesn't try to ssh to itself
    continue
 fi
    echo "Connecting to - $server"
    ssh "$server"   #SSH login
    echo Connected to "$serverName"
    exec < filelist.txt
    while read updatedfile oldfile; do
    #   echo updatedfile = $updatedfile #use for troubleshooting
    #   echo oldfile = $oldfile   #use for troubleshooting
               if [[ ! $updatedfile =~ [^[:space:]] ]] ; then  #empty line exception
                continue # empty line exception
               fi
               if [[ ! $oldfile =~ [^[:space:]] ]] ; then  #empty line exception
                continue # empty line exception
               fi 
            echo Comparing $updatedfile with $oldfile
            if diff "$updatedfile" "$oldfile" >/dev/null ; then
                echo The files compared are the same. No changes were made.
            else
                echo The files compared are different.
                cp -f -v $oldfile /infanass/dev/admin/backup/`uname -n`_${oldfile##*/}_$(date +%F-%T)
                cp -f -v $updatedfile $oldfile 
            fi          
    done        
 done 3</infanass/dev/admin/servers.txt

I want to run the block of code after sshing to the servers.

Answer 1

The problem you're having currently is that the SSH connection "pauses" the script, and the script resumes with the echo Connected to "$serverName" line only after the SSH session exits.

As I see it, you have two options. (There are probably more, but these are the two I can think of currently.)

Option one is to use expect to start an SSH session you can control through the script, effectively sending commands back and forth from the master script to the SSH session. Option two is to put the block you want to run remotely on the remote server as a different script, and run SSH in a non-interactive way: ssh $server $script-to-run.

Answer 2

If you're absolutely convinced that you want to structure this as a single script you can make use of a HEREDOC when you open your connection to the remote ssh server.

For example:

$ ssh user@server << EOT

...
commands
...

EOT

Answer 3

Alternatively, simple echo to pipe and then execute all from stdin.

echo " \
uname -a; \
whoami; \
uname " \
| ssh -l root localhost 'cat | sh -'