Hit StackOverflow's API and save to a file.

fetchTags.php

<?php
/**
 * This script hits StackOverflow's API and prints the results out to a file in JSON format.
 *
 * This script is specifically targeted at tags, but you could manipulate it target other things.
 */

$file = fopen('/mnt/projects/tags.txt', 'a');

/**
 * Create a filter an pick a site here: https://api.stackexchange.com/docs/create-filter
 * This example uses a filter created here: https://api.stackexchange.com/docs/tags
 * This filter will fetch tags.
 *
 * This script requires that your filter include the following variables:
 * - has_more
 * - quota_remaining
 */
$filter = '!*MPoAKy)55yzL2y';
$site = 'stackoverflow';
$pageSize = 100; // limit is 100
$pages = 999; // You will probably run out of results or hit your quota before a high number like 999 is reached

// Just keeping track of how many we've processed:
$count = 0;

// If we want to rate limit by time, in seconds:
$timeBetweenCurls = 0.5;

$curl = curl_init();

$items = [];
$reponse = null;

$forcedExit = false;

$processedCount = 0;

print("Pages processed:\n");

for ($i = 1; $i <= $pages; $i++) {
    print('.');
    $url = 'https://api.stackexchange.com/2.2/tags?page=' . $i . '&pagesize=' . $pageSize . '&order=asc&sort=name&site=' . $site . '&filter=' . $filter;

    curl_setopt($curl, CURLOPT_URL, $url);
    curl_setopt($curl, CURLOPT_ENCODING, 'gzip'); // StackOverflow's API encodes its responses
    curl_setopt($curl, CURLOPT_RETURNTRANSFER, 1);

    $response = json_decode(curl_exec($curl), true);

    foreach ($response['items'] as $item) {
        array_push($items, $item);
        $processedCount++;
    }

    if (!$response['has_more']) {
        $forcedExit = true;
        print("\nNo results left.");
        break;
    } else if ($response['quota_remaining'] == 0) {
        $forcedExit = true;
        print("\nQuota exceeded.");
        break;
    }

    sleep($timeBetweenCurls);
}

print("\nPrinting to file...");

fwrite($file, json_encode($items));
curl_close($curl);
fclose($file);

if (!$forcedExit) {
    print("\nFinished without error.");
}

print("\nRemaining quota is " . $response['quota_remaining'] . ".");

print("\nProcessed " . $processedCount . " items.");

print("\nExiting...\n");