Regex to match all lines except duplicate

Question

I have this text:

156.48.459.20 - - [11/Aug/2019
156.48.459.20 - - [11/Aug/2019
235.145.41.12 - - [11/Aug/2019
235.145.41.12 - - [11/Aug/2019
66.23.114.251 - - [11/Aug/2019

I want to match all lines that is from the current day so i made this simple regex '/.*11\/Aug\/2019.*'.

As you can see there's two duplicated IPs in the text, i don't want to match the duplicated lines, so i searched a bit and i found this regex: (.).*\1 DEMO although this regex is kinda weird i tried to apply it in my current regex, so i did: (.*11\/Aug\/2019.*)\1, it did not worked. Could someone help?

This is my desired result:

156.48.459.20 - - [11/Aug/2019
235.145.41.12 - - [11/Aug/2019
66.23.114.251 - - [11/Aug/2019

NOTE: i'm using the function preg_match_all():

preg_match_all('/(.*11\/Aug\/2019.*)\1/', $input_lines, $output_array);

Answer 1

Is pure regex a requirement?

You can use PHP to get uniques:

<?php
$input_lines = '156.48.459.20 - - [11/Aug/2019
156.48.459.20 - - [11/Aug/2019
235.145.41.12 - - [11/Aug/2019
235.145.41.12 - - [11/Aug/2019
66.23.114.251 - - [11/Aug/2019';

preg_match_all( '/.*11\/Aug\/2019/m', $input_lines, $output_array );

// PHP associative array abuse incoming
// Flip the array so that the values become keys and flip it back
// This guarantees that only uniques survive
$output_array[ 0 ] = array_keys( array_flip( $output_array[ 0 ] ) );

var_dump( $output_array );

Outputs:

array(1) {
  [0]=>
  array(3) {
    [1]=>
    string(30) "156.48.459.20 - - [11/Aug/2019"
    [3]=>
    string(30) "235.145.41.12 - - [11/Aug/2019"
    [4]=>
    string(30) "66.23.114.251 - - [11/Aug/2019"
  }
}