Why can only download the first episode video on bilibili with youtube-dl?

I can download the first episode of a series.

 yutube-dl  https://www.bilibili.com/video/av90163846?p=1

Now I want to download all episodes of the series.

for i in $(seq  1  55)
do
    yutube-dl  https://www.bilibili.com/video/av90163846?p=$i
done

All other episodes except the first can't be downloaded ,both of them contains same error info such as below:

[BiliBili] 90163846: Downloading webpage
[BiliBili] 90163846: Downloading video info page
[download] 【合集300集全】地道美音 美国中小学教学 自然科学 社会常识-90163846.flv has already been downloaded

Please have a try and check what happens,how to fix then?
@Christos Lytras,strange thing happen with your code:

for i in $(seq  1  55)
do
    youtube-dl https://www.bilibili.com/video/av90163846?p=$i -o "%(title)s-%(id)s-$i.%(ext)s"
done

It surely can download video on bilibili,but all of downloaded video have different name and same content,all the content are the same as the first episode,have a try and check ,you will find that fact.

Solution

This error occurs because youtube-dl ignores URI parameters after ? for the filename, so the next file it tries to download has the same name with the previous one and it fails because a file already exists with that name. The solution is to use the --output template filesystem option to set a filename which it'll have an index in its name using the variable i.

Filesystem Options
-o, --output TEMPLATE            Output filename template, see the "OUTPUT
                                 TEMPLATE" for all the info
OUTPUT TEMPLATE

The -o option allows users to indicate a template for the output file names.

The basic usage is not to set any template arguments when downloading a single file, like in youtube-dl -o funny_video.flv "https://some/video". However, it may contain special sequences that will be replaced when downloading each video. The special sequences may be formatted according to python string formatting operations. For example, %(NAME)s or %(NAME)05d. To clarify, that is a percent symbol followed by a name in parentheses, followed by formatting operations. Allowed names along with sequence type are:

id (string): Video identifier
title (string): Video title
url (string): Video URL
ext (string): Video filename extension
...

For your case, to use the i in the output filename, you can use something like this:

for i in $(seq  1  55)
do
    youtube-dl https://www.bilibili.com/video/av90163846?p=$i -o "%(title)s-%(id)s-$i.%(ext)s"
done

which will use the title the id the i variable for indexing and the ext for the video extension.

You can check the Output Template variables for more options defining the filename.

UPDATE

Apparently, bilibili.com has some Javascript involved to setup the video player and fetch the video files. There is no way so you can extract the whole playlist using youtube-dl. I suggest you use Lux which supports Bilibili playlists out of the box. It has installers for all major operating systems and you can use it like this to download the whole playlist:

lux -p https://www.bilibili.com/video/av90163846

of if you want to download only until 55 video, you can use -end 55 cli option like this:

lux -end 55 -p https://www.bilibili.com/video/av90163846

You can use the -start, -end or -items option to specify the download range of the list:
-start
      Playlist video to start at (default 1)
-end
      Playlist video to end at
-items
      Playlist video items to download. Separated by commas like: 1,5,6,8-10
For bilibili playlists only:
-eto
      File name of each bilibili episode doesn't include the playlist title

If you want to only get information of a playlist without downloading files, then use the -i command line option like this:

lux -i -p https://www.bilibili.com/video/av90163846

will output something like this:

 Site:      哔哩哔哩 bilibili.com
 Title:     【合集300集全】地道美音 美国中小学教学 自然科学 社会常识 P1 【001】Parts of Plants
 Type:      video
 Streams:   # All available quality
     [64]  -------------------
     Quality:         高清 720P
     Size:            308.24 MiB (323215935 Bytes)
     # download with: lux -f 64 ...

     [32]  -------------------
     Quality:         清晰 480P
     Size:            201.57 MiB (211361230 Bytes)
     # download with: lux -f 32 ...

     [16]  -------------------
     Quality:         流畅 360P
     Size:            124.75 MiB (130809508 Bytes)
     # download with: lux -f 16 ...


 Site:      哔哩哔哩 bilibili.com
 Title:     【合集300集全】地道美音 美国中小学教学 自然科学 社会常识 P2 【002】Life Cycle of a Plant
 Type:      video
 Streams:   # All available quality
     [64]  -------------------
     Quality:         高清 720P
     Size:            227.75 MiB (238809781 Bytes)
     # download with: lux -f 64 ...

     [32]  -------------------
     Quality:         清晰 480P
     Size:            148.96 MiB (156191413 Bytes)
     # download with: lux -f 32 ...

     [16]  -------------------
     Quality:         流畅 360P
     Size:            94.82 MiB (99425641 Bytes)
     # download with: lux  -f 16 ...