PHP script to find duplicates & unique entries among two separate files

get_duplicates.php

<?php

/**
 * PHP script to find duplicates & unique entries among two
 * separate files.
 *
 * The script outputs one file with the matching lines and
 * one with the unique ones.
 *
 * Example:
 *
 * File 1:
 *   banana
 *   apple
 *   pear
 *   pineapple
 *   apple
 *
 * File 2:
 *   pineapple
 *   strawberry
 *   apple
 *   mango
 *   kiwi
 *
 * Output 1 (duplicates):
 *   apple
 *   pineapple
 *
 * Output 2 (unique entries):
 *   banana
 *   apple
 *   pear
 *   pineapple
 *   strawberry
 *   mango
 *   kiwi
 *
 * TODO: Generalize the script to accept N input files. N could also
 * be 1, in which case the script just removes duplicates from the
 * input file.
 *
 * TODO: Verify that newline characters don't mess the match, ex.
 * if the last line does not end with a newline
 */


// ======================================================================================
// =                                   User input                                       =
// ======================================================================================

/* Input files */
$input_file_1 = $argv[1];
$input_file_2 = $argv[2];

/* Output files */
$output_in_common = isset($argv[3]) ? $argv[3] : "DUPLICATES.csv";
$output_unique = isset($argv[4]) ? $argv[4] : "UNIQUES.csv";

/* Should the match take into account case differences? */
$case_insensitive = true;


// ======================================================================================
// =                                Actual script                                       =
// ======================================================================================

/* Extract data from files */
$array_1 = file ($input_file_1);
$array_2 = file ($input_file_2);

if ($case_insensitive) {
  $array_1 = array_map ('strtolower', $array_1);
  $array_2 = array_map ('strtolower', $array_2);
}

/* Extract unique entries in each file */
$unique_1 = array_unique ($array_1);
$unique_2 = array_unique ($array_2);
$n_unique_1 = count (array_unique ($array_1));
$n_unique_2 = count (array_unique ($array_2));

/* Find common lines between the two files */
$merge = array_merge ($array_1, $array_2);
$in_common = array();
$unique = array();
foreach (array_count_values($merge) as $value => $count)
  if ($count > 1)
    $in_common[] = $value;
  else if ($count == 1)
    $unique[] = $value;
$n_in_common = count ($in_common);

/* Print some information to screen */
echo "$input_file_1 has ".count($array_1)." elements ($n_unique_1 unique)" . PHP_EOL;
echo "$input_file_2 has ".count($array_2)." elements ($n_unique_2 unique)" . PHP_EOL;
echo "They have $n_in_common lines in common" . PHP_EOL;

/* Create and fill output files */
file_put_contents ($output_in_common, join ($in_common));
file_put_contents ($output_unique, join ($unique));

?>