Search string pattern in each file and print its line number

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PHP

The filename is files_in_dir.php
In the working directory there is a folder. That name is files_test .
In that folder there are two text file:

file1.txt contains:

AAAAAAAA
BBBBBBBB
CCCCCCCC
DDDDDDDD

file2.txt contains:

AAAAAAAA
BBBBBBBB
DDDDDDDD
CCCCCCCC

We are searching for "CCCCCCCC" pattern and want to know its line number and echo $line_number of each file. That's all!

What I have tried:

<?php
//CURRENT FILE NAME IS: files_in_dir.php
//My working directory: /home/Zoltan/Dokumentumok
$files = array_diff(scandir("files_test"), array('..', '.'));
//Files scanned into $files from files_test folder

echo getcwd()."\n";

echo "THINGS IN WORKING DIRECTORY";
//Files and folder listed in working directory
foreach (scandir('.') as $file)
    echo $file . "\n";
    
echo "\n";

//Now I would like to find which line is in the CCCCCCCC pattern in each file in files_test directory
foreach($files as $file) {
  echo $file."\n";
  $search      = "CCCCCCCC";
//BUT THE NEXT LINE DOES NOT WORK
  $lines       = file($file);
  $line_number = false;
  
  while (list($key, $line) = each($lines) and !$line_number) {
   $line_number = (strpos($line, $search) !== FALSE) ? $key + 1 : $line_number;
  }
//And print the line number
  echo "The line number is: ".$line_number."\n";

}
?>