A simple PHP script that uses the Slack API to automatically delete old files and outputs all errors it encounters.

slack-delete-old-files.php

<?php

// https://api.slack.com/methods/files.list
const SLACK_API_FILES_LIST = 'https://slack.com/api/files.list';

// https://api.slack.com/methods/files.delete
const SLACK_API_FILES_DELETE = 'https://slack.com/api/files.delete';

// retrieved from https://api.slack.com/web
// needs to be admin profile token
const API_TOKEN = '';

// this should be a string like "-1 month". Fed directly to strototime()
const OLDEST_ALLOWED_FILE = '-1 month'; 

// set timezone to UTC to prevent warnings and to put request in sync with Slack API
date_default_timezone_set('UTC');

$filesDeleted = 0;

while (true) {
    $files = getFiles();

    try {
        output(sprintf('Found %s files to delete', @count($files['files'])));
        if ($files['files']) {
            foreach ($files['files'] as $file) {
                deleteFile($file['id']);
                $filesDeleted++;
            }
        } else {
            break;
        }
    } catch (\Exception $ex) {
        output($ex->getMessage());
    }
}

output(sprintf('Deleted %s files', $filesDeleted));





function output($message) {
    echo sprintf('[%s] %s %s', date('c'), $message, PHP_EOL);    
}

function getFiles() {
    $curl = curl_init();
    curl_setopt ($curl, CURLOPT_URL, sprintf('%s?token=%s&ts_to=%s', SLACK_API_FILES_LIST, API_TOKEN, strtotime(OLDEST_ALLOWED_FILE)));
    curl_setopt($curl, CURLOPT_RETURNTRANSFER, 1);
    $result = curl_exec ($curl);

    if ($result === false) {
        output(sprintf('Curl error (%s): %s', SLACK_API_FILES_LIST, curl_error($curl)));
        die();
    }

    curl_close ($curl);
    $result =  json_decode($result, true);

    if (@$result['ok'] === false) {
        output(sprintf('[%s] API Error: %s', SLACK_API_FILES_LIST, $result['error']));
        die();
    }

    return $result;
}

function deleteFile($id) {
    $curl = curl_init();
    curl_setopt($curl, CURLOPT_URL, SLACK_API_FILES_DELETE);
    curl_setopt($curl, CURLOPT_POST, 2);
    curl_setopt($curl, CURLOPT_RETURNTRANSFER, 1);
    curl_setopt($curl, CURLOPT_POSTFIELDS, sprintf('token=%s&file=%s', API_TOKEN, $id));
    $result = curl_exec ($curl);

    if ($result === false) {
        output(sprintf('Curl error (%s): %s', SLACK_API_FILES_DELETE, curl_error($curl)));
        die();
    }

    curl_close ($curl);
    $result =  json_decode($result, true);

    if (@$result['ok'] === false) {
        output(sprintf('[%s] API Error: %s', SLACK_API_FILES_DELETE, $result['error']));
        die();
    }

    return $reuslt;
}

Typo on line 92 -> return $reuslt

Thank you for this!