Using Bash to search files for - bash

Question

I have two text files, 1 with a unique list of IP addresses and the other with a longer list of an IP address population. I am trying to identify what IP addresses from the unique list appear in the longer population list using bash.
So far I have:
#!/bin/bash
while read line; do
grep -Ff "$line" population.txt
done < $uniqueIP.txt
The script runs but I get no output. I am trying to count the number of occurrences but having issues coming up with the logic. Currently, the script does not output anything.
Sample Input:
uniqueIP.txt
192.168.1.10
192.168.1.11
192.168.1.12
192.168.1.13
192.168.1.14
population.txt
192.168.1.12
192.168.1.14
192.168.1.15
192.168.1.16
192.168.1.17
192.168.1.18
192.168.1.19
192.168.1.22
192.168.1.23
Sample Output:
Found: 192.168.1.12
Found: 192.168.1.14
Total: 2

Answer 1

Here is my suggested bash function count_unique_ips for your problem
#!/bin/bash
function count_unique_ips()
{
local unique_ips_file=$1
local population_file=$2
local unique_ip_list=$(tr ' ' '\n' < ${unique_ips_file} | sort | uniq)
for ip in "${unique_ip_list[#]}"; do
count=$(grep -o -i ${ip} ${population_file} | wc -l)
echo "'${ip}': ${count}"
done
}
count_unique_ips uniqueIP.txt population.txt
You should get the following output based on 2 given input files uniqueIP.txt and population.txt
'192.168.1.10': 0
'192.168.1.11': 0
'192.168.1.12': 1
'192.168.1.13': 0
'192.168.1.14': 1

Answer 2

A short method, using only grep, could be
grep -Fxf uniqueIP.txt population.txt
but this would be slow for large files. A faster way is
sort uniqueIP.txt population.txt | uniq -d
assuming the IPs in population.txt are also unique within this file, and one IP per line without extra characters (including blank characters).