Using Bash to search files for

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).