UNIX for Advanced & Expert Users

   for i in `cat file1` 
      do 
        for j in `cat file2`
        do
         ssh $i 'systemctl is-enabled "${j}" ';
      done
    done
    
   for i in `cat file1` 
      do 
        for j in `cat file2`
        do
         ssh $i 'systemctl is-enabled "$j" ';
      done
    done
    
   for i in `cat file1` 
      do 
        for j in `cat file2`
        do
         ssh $i 'systemctl is-enabled \$j ';
      done
    done
    
   for i in `cat file1` 
      do 
        for j in `cat file2`
        do
         ssh $i 'systemctl is-enabled \\$j ';
      done
    done
    
   for i in `cat file1` 
      do 
        for j in `cat file2`
        do
         ssh $i 'systemctl is-enabled \\\$j ';
      done
    done
    
   for i in `cat file1` 
      do 
        for j in `cat file2`
        do
         ssh $i 'systemctl is-enabled \\\\$j ';
      done
    done

ssh <<!
remotenode  "$j"
!

echo 'File not found in '"$PWD"', please re-enter'

   for i in `cat file1` 
      do 
        for j in `cat file2`
        do
         ssh $i 'systemctl is-enabled '"$j";
      done
    done

ssh $i "systemctl is-enabled ${j}";               # No quotes around the variable being passed
ssh $i "systemctl is-enabled '${j}'";             # Wraps single quotes around variable being passed, interpreted locally but not interpreted again remotely
ssh $i "systemctl is-enabled \"${j}\"";           # Wraps double quotes around variable being passed, interpreted locally but could then be interpreted again remotely if the variable is a remote variable name or subshell

while read -u11 outer_variable                                            # Read from file descriptor 11
do
   while read -u12 inner_variable                                         # Read from file descriptor 12
   do
      ssh "${user}@${outer_variable}" "foo bar \"${inner_variable}\""
   done 12< "${inner_variable_input_file}"                                # Supply input file on file descriptor 12
done 11< "${outer_variable_input_file}"                                   # Supply input file on file descriptor 11

for i in `cat file1`                            # useless use of cat, may fail on spaces in file1's lines, `...` deprecated
  do 
  for j in `cat file2`                          # same as above; plus: opens, reads, closes file2 linecount1 times
    do
    ssh $i 'systemctl is-enabled "${j}" ';      # creates and deletes a remote network login (linecount1 * linecount2) times
    done
  done

mapfile -t j < file2
while read i
  do    ssh ${i}  <<-EOFSSH
        $(for X in ${!j[@]}
            do echo "systemctl is-enabled ${j[X]}"
            done)
        EOFSSH
   done <  file1

mapfile -t j < file2
IFS=$'\n'
while read i
  do    ssh -T ${i}  <<< "${j[*]/#/systemctl is-enabled }"
  done <  file1