Accessing array elements by index on a remote machine via ssh

On a remote machine, I need to get the values ​​of 2 arrays at the same time. That is, 1 element of 1 and 2 arrays, then 2 element of 1 and 2 arrays, and so on.

When writing a script, I ran into a problem that when I specify the array index using a variable, only the first element of the array is displayed and that's it. I tried escaping and writing like this [$i] but no result. What am I doing wrong? And what is the right way to access array elements by index?

What i want to get:

array1=("1" "2")
array2=("a" "b")

ssh $user_srv@$ip_srv -p $port_srv 'bash -s' << EOF
for i in "${!array1[@]}"
do
    echo '${array1[$i]}'
    echo '${array2[$i]}'
done
EOF

Result:

1
a
2
b

Define the code you want to run as a local function; then use declare -f to serialize that function, and declare -p to serialize the data it uses, to pass them over the wire.

array1=("1" "2")
array2=("a" "b")

rmt_func() {
  for i in "${!array1[@]}"; do
    echo "${array1[$i]}"
    echo "${array2[$i]}"
  done
}

ssh "$user_srv@$ip_srv" -p "$port_srv" 'bash -s' <<EOF
  $(declare -p array1 array2)
  $(declare -f rmt_func)
  rmt_func
EOF

Since the arrays don't exist on the remote machine, this code solves the problem by looping through the arrays on the local machine and generating printf commands to send to the remote machine to print the elements:

array1=("1" "2")
array2=("a" "b")

for i in "${!array1[@]}"; do
    printf 'printf "%%s\\\\n" %q\n' "${array1[i]}"
    printf 'printf "%%s\\\\n" %q\n' "${array2[i]}"
done | ssh "$user_srv@$ip_srv" -p "$port_srv" 'bash -s'

• The %q format with printf causes the corresponding argument (in this case an array element) to be output in a format that can be reused as shell input. That ensures that the code works for array elements that contain whitespace or shell metacharacters.
• echo is not safe for printing arbitrary string values so I used printf instead. See the accepted, and excellent, answer to Why is printf better than echo?.