Best timing method? - bash

Question

I'm trying to write an SSH version of ICMP Ping, as follows:
TARGET_IP=""
count=0
time_start=0
time_end=0
time_taken=0
TARGET_IP=$1
while [ $count -lt 5 ]
do
((count=count+1))
time_start=$(date +%s%N)
temp_target_key=$(ssh-keyscan $TARGET_IP) > /dev/null 2>&1
time_end=$(date +%s%N)
time_taken=$((( $time_end - $time_start ) / 1000000))
echo "Time taken=$time_taken ms."
target_key=$(echo $temp_target_key | awk '{print $3}') > /dev/null 2>&1
echo $temp_target_key > target_key.txt
ssh-keygen -l -f target_key.txt > /dev/null 2>&1
test=$?
if [ $test -ne 0 ]
then
echo "Device returned invalid RSA Public Key"
echo -e "\n"
echo -e "\n"
else
echo "Device responding correctly."
echo -e "\n"
fi
done
exit
ICMP Ping reports ping times of 5ms compared to this script reporting 300ms for the same device. I realise that I'm timing the script AND device programming/firmware response times too, but am I doing this the best way please?
Thanks

Answer 1

I can't see a better method to simulate a ssh ping. Nevertheless I've tried to improve your script in a more pure bash style:
#! /bin/bash
if (($# != 1)); then
echo "Usage: ${0##*/} host" >&2
exit 1
fi
TARGET_IP="$1"
target_key_file="target_key.txt"
for ((count=0; count < 5; count++))
do
time_start=$(date +%s%N)
temp_target_key=$(ssh-keyscan "$TARGET_IP") > /dev/null 2>&1
time_end=$(date +%s%N)
time_taken=$(((time_end - time_start ) / 1000000))
echo "Time taken=$time_taken ms."
read _ _ target_key _ <<< "$temp_target_key"
echo "$target_key"
echo "$temp_target_key" >| "$target_key_file"
if ! ssh-keygen -l -f "$target_key_file" > /dev/null 2>&1
then echo -e "Device returned invalid RSA Public Key.\n\n"
else echo -e "Device responding correctly.\n\n"
fi
done