Slack delete all your files (rewrite of https://gist.github.com/jamescmartinez/909401b19c0f779fc9c1)

run.php

<?php
<<<CONFIG
packages:
    - "kriswallsmith/buzz: ^0.15.0"
    - "symfony/console: ^3.2@dev"
CONFIG;

// Find you token on https://api.slack.com/docs/oauth-test-tokens

use Buzz\Message\Response;
use Symfony\Component\Console\Application;
use Symfony\Component\Console\Helper\ProgressBar;
use Symfony\Component\Console\Input\InputArgument;
use Symfony\Component\Console\Input\InputInterface;
use Symfony\Component\Console\Output\OutputInterface;
use Symfony\Component\Console\Question\ConfirmationQuestion;

(new Application())
    ->register('delete-files')
        ->addArgument('token', InputArgument::REQUIRED)
        ->setCode(function(InputInterface $input, OutputInterface $output) {
            $token = $input->getArgument('token');
            $validateResponse = function( $response) {
                $responseDecoded = json_decode($response->getContent(), true);

                if (!$responseDecoded) {
                    throw new \Exception('Something goes wrong. Unable to decode the response.');
                }

                if (!$responseDecoded['ok']) {
                    throw new \Exception('Something goes wrong. Error: '.$responseDecoded['error']);
                }

                return $responseDecoded;
            };
            $client = new Buzz\Browser();

            // get "all" files
            $response = $client->get('https://slack.com/api/files.list?'.http_build_query([
                'token' => $token,
                'count' => 1000,
                'ts_to' => (new \DateTime('-5 months'))->format('U'),
            ]));
            $responseDecoded = $validateResponse($response);

            $total = $responseDecoded['paging']['total'];

            // Validate
            $q = new ConfirmationQuestion(sprintf('You are going to delete %d files, are you sure? [Y/n]', $total));
            if (!$this->getHelper('question')->ask($input, $output, $q)) {
                $output->writeln('Abort the mission');

                return;
            }

            // delete
            $bar = new ProgressBar($output, $total);
            foreach ($responseDecoded['files'] as $file) {
                $response = $client->get('https://slack.com/api/files.delete?'.http_build_query([
                    'token' => $token,
                    'file' => $file['id'],
                ]));
                $validateResponse($response);
                $bar->advance();
            }

            $output->writeln('Done');
        })
    ->getApplication()
    ->setDefaultCommand('delete-files', true)
    ->run()
;