return isset($_ENV['VAPOR_ARTIFACT_NAME']) ? 's3' : 'public'; が分からない。

前提・実現したいこと

laravel8　jetstreamを利用しています。
jetstreamのprofileを更新するときの、HasProfilePhoto.phpの中の79行目について、構文を教えていただきたいです。

return isset($_ENV['VAPOR_ARTIFACT_NAME']) ? 's3' : 'public';
という文の意味について教えていただきたいです。

該当のソースコード

php
1<?php
2
3namespace Laravel\Jetstream;
4
5use Illuminate\Http\UploadedFile;
6use Illuminate\Support\Facades\Storage;
7use Laravel\Jetstream\Features;
8
9trait HasProfilePhoto
10{
11    /**
12     * Update the user's profile photo.
13     *
14     * @param  \Illuminate\Http\UploadedFile  $photo
15     * @return void
16     */
17    public function updateProfilePhoto(UploadedFile $photo)
18    {
19        tap($this->profile_photo_path, function ($previous) use ($photo) {
20            $this->forceFill([
21                'profile_photo_path' => $photo->storePublicly(
22                    'profile-photos', ['disk' => $this->profilePhotoDisk()]
23                ),
24            ])->save();
25
26            if ($previous) {
27                Storage::disk($this->profilePhotoDisk())->delete($previous);
28            }
29        });
30    }
31
32    /**
33     * Delete the user's profile photo.
34     *
35     * @return void
36     */
37    public function deleteProfilePhoto()
38    {
39        if (! Features::managesProfilePhotos()) {
40            return;
41        }
42
43        Storage::disk($this->profilePhotoDisk())->delete($this->profile_photo_path);
44
45        $this->forceFill([
46            'profile_photo_path' => null,
47        ])->save();
48    }
49
50    /**
51     * Get the URL to the user's profile photo.
52     *
53     * @return string
54     */
55    public function getProfilePhotoUrlAttribute()
56    {
57        return $this->profile_photo_path
58                    ? Storage::disk($this->profilePhotoDisk())->url($this->profile_photo_path)
59                    : $this->defaultProfilePhotoUrl();
60    }
61
62    /**
63     * Get the default profile photo URL if no profile photo has been uploaded.
64     *
65     * @return string
66     */
67    protected function defaultProfilePhotoUrl()
68    {
69        return 'https://ui-avatars.com/api/?name='.urlencode($this->name).'&color=7F9CF5&background=EBF4FF';
70    }
71
72    /**
73     * Get the disk that profile photos should be stored on.
74     *
75     * @return string
76     */
77    protected function profilePhotoDisk()
78    {
79        return isset($_ENV['VAPOR_ARTIFACT_NAME']) ? 's3' : config('jetstream.profile_photo_disk', 'public');
80    }
81}