Remote server array args in for loop - bash

Question

I need to pass values from an array to the script on remote host.
The remote script creates files locally on each array value.
Yes, i can do it by:
for i in ${LIST[#]}
do ssh root#${servers} bash "/home/test.sh" "$i"
done
but this action is rather slow and it makes ssh session on every array value
ssh root#${servers} bash "/home/test.sh" "${LIST[#]}"
by this code i get an error:
bash: line 1338: command not found
How can i do it?

Answer 1

Use the connection-sharing feature of ssh so that you only have a single, preauthenticated connection that is used by each ssh process in your loop.
# This is the socket all of the following ssh processes will use
# to establish a connection to the remote host.
socket=~/.ssh/ssh_mux
# This starts a background process that does nothing except keep the
# authenticated connection open on the specified socket file.
ssh -N -M -o ControlPath="$socket" root#${servers} &
# Each ssh process should start much more quickly, as it doesn't have to
# go through the authentication protocol each time.
for i in "${LIST[#]}"; do
# This uses the existing connection to avoid having to authenticate again
ssh -o ControlPath="$socket" root#${servers} "bash /home/test.sh '$i'"
# The above command is still a little fragile, as it assumes that $i
# doesn't have a single quote in its name.
done
# This closes the connection master
ssh -o ControlPath="$socket" -O exit root#{servers}
The alternative is to try to move your loop into the remote command, but this is fragile as the array isn't defined on the remote host, and there is no good way to transfer each element in a way that protects each element. If you weren't concerned about word-splitting, you could use
ssh root#${servers} "for i in ${LIST[*]}; do bash /home/test.sh \$i; done"
but then you probably wouldn't be using an array in the first place.