MinasMazar's blog ~ dev stuff

Inspiration (and code stolen 🤪) from this Medium article (errr… Freedium 😎)

This is useful when you try to download a web page that does not display some contents if the browser agent you're using does not exec any js code (i.e EWW).

1. setup a new nodejs project mkdir html-fetch && node init --yes
2. add node-fetch dependency into the package.json and npm install
3. create the index.js source file with the content as follow:

const fetch = require("node-fetch");
const fs = require("fs");
// you can update this to any website you want to download
const site = "https://www.youtube.com/@BorderNightsOfficial";
// you can update this if you want to save
const filename = "index.html";
// fetch url
fetch(site, {
  headers: {
    // some sites require a user-agent header to return the webpage
    "User-Agent":
    "Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:97.0) Gecko/20100"},
}).then((res) => {
  // get text from Response stream
  return res.text();
}).then((text) => {
  // write html from response to index.html
  fs.writeFile(filename, text, () => {});
});

Run it via node index.js. This will fetch the page into the index.html file.

Bind to

docker run --rm --name postgres --volume ~/postgres-data:/var/lib/postgresql/data postgres:latest

Backup volume with

tar cf postgres-data_$(format-time-string "%N").tar postgres-data

docker image prune -a

docker system prune will delete all dangling data (containers, networks, and images)

More info in this StackOverflow thread.

# Add Docker's official GPG key:
sudo apt-get update
sudo apt-get install ca-certificates curl
sudo install -m 0755 -d /etc/apt/keyrings
sudo curl -fsSL https://download.docker.com/linux/ubuntu/gpg -o /etc/apt/keyrings/docker.asc
sudo chmod a+r /etc/apt/keyrings/docker.asc

# Add the repository to Apt sources:
echo \
  "deb [arch=$(dpkg --print-architecture) signed-by=/etc/apt/keyrings/docker.asc] https://download.docker.com/linux/ubuntu \
  $(. /etc/os-release && echo "${UBUNTU_CODENAME:-$VERSION_CODENAME}") stable" | \
  sudo tee /etc/apt/sources.list.d/docker.list > /dev/null
sudo apt-get update

sudo apt-get install docker-ce docker-ce-cli containerd.io docker-buildx-plugin docker-compose-plugin

Verify that the installation is successful by running the hello-world image:

sudo docker run hello-world

Follow the instructions in the Docker documentation. Before you can install Docker Engine, you need to uninstall any conflicting packages. Distro maintainers provide an unofficial distributions of Docker packages in APT. You must uninstall these packages before you can install the official version of Docker Engine.

#!/bin/bash

# Uninstall unofficial distributions of Docker packages in APT

sudo apt-get purge docker-ce docker-ce-cli containerd.io docker-buildx-plugin docker-compose-plugin docker-ce-rootless-extras

# Remove images, containers, volumes, or custom configuration files 

sudo rm -rf /var/lib/docker
sudo rm -rf /var/lib/containerd

# Add Docker's official GPG key:
sudo apt-get update
sudo apt-get install ca-certificates curl
sudo install -m 0755 -d /etc/apt/keyrings
sudo curl -fsSL https://download.docker.com/linux/raspbian/gpg -o /etc/apt/keyrings/docker.asc
sudo chmod a+r /etc/apt/keyrings/docker.asc

# Set up Docker's APT repository:
echo \
  "deb [arch=$(dpkg --print-architecture) signed-by=/etc/apt/keyrings/docker.asc] https://download.docker.com/linux/raspbian \
  $(. /etc/os-release && echo "$VERSION_CODENAME") stable" | \
  sudo tee /etc/apt/sources.list.d/docker.list > /dev/null
sudo apt-get update

# Install Docker packages
sudo apt-get install docker-ce docker-ce-cli containerd.io docker-buildx-plugin docker-compose-plugin

# Verify that the installation is successful by running the hello-world image:
sudo docker run hello-world

Remember to keep the Build and App images in sync (see here)

When building an image, you can see an error like cannot find the image for the platform…. Consider to add --platform arm64 flag to the docker build command. Here's the official Docker documentation for this flag. Also keep an eye to this file to get a list of platforms. Remember you can detect the platform of the current machine via uname -a.

If you're using Docker to run Elixir, you can face an error like this during the dependencies compilation:

could not compile dependency :ssl_verify_fun, "mix compile" failed. Errors may have been logged above. You can recompile this dependency with "mix deps.compile ssl_verify_fun", update it with "mix deps.update ssl_verify_fun" or clean it with "mix deps.clean ssl_verify_fun"

In this case, install the erlang-public-key package should solve the issue.

The Raspbian issue: another error that can occur while building a docker image on Raspbian that uses apt-get commands is

ERROR: failed to solve: process "/bin/sh -c apt-get update -y &&   apt-get install -y libstdc++6 openssl libncurses5 locales ca-certificates &&   apt-get clean && rm -f /var/lib/apt/lists/*_*" did not complete successfully: exit code: 159

It seems there's a problem with libseccomp; according to this SO thread the solution is to upgrade libseccomp manually on the host system: download here and sudo dpkg -i libseccomp2_2.4.3-1+b1_armhf.deb.

• https://github.com/teslamate-org/teslamate/issues/3691

source: https://stackoverflow.com/questions/40136606/how-to-expose-audio-from-docker-container-to-a-mac

You need to install PulseAudio

brew install pulseaudio

Start the server

pulseaudio --load=module-native-protocol-tcp --exit-idle-time=-1 --daemon

In your Docker container:

• install PulseAudio, e.g., apt-get install pulseaudio.
• set the following environment variable: ENV PULSE_SERVER\=host.docker.internal

You can run a test to see if it's working like this:

docker run -it -e PULSE_SERVER=host.docker.internal --mount type=bind,source=/Users/YOURUSERNAME/.config/pulse,target=/home/pulseaudio/.config/pulse --entrypoint speaker-test --rm jess/pulseaudio -c 2 -l 1 -t wav

• Toolbox
• Metaprogramming: The Elixir AST
• Mix dependencies
• Learn Elixir (learn-elixir.dev/#hiring)

• https://betterprogramming.pub/notes-on-clustering-elixir-applications-49707ed53910
• https://hexdocs.pm/libcluster/readme.html

Good readings about this topic:

• https://medium.com/hackernoon/running-distributed-erlang-elixir-applications-on-docker-b211d95affbe
• https://www.erlang-solutions.com/blog/erlang-and-elixir-distribution-without-epmd/

Here's a talk I still have to watch https://www.youtube.com/watch?v=F_YUyd_Qdjs

Follow this link to Elixir forum post.

It will probably faster and for sure will cope a lot more under load, due to the BEAM, that is well exemplified here by @sasajuric.

We already have several projects in Elixir fore ecommerce:

• Crimsom repo and article.
• Shopix repo and aritcle.
• Freshcom repos. They have separated it in several repos.
• Many more here.

I don’t really know if any of them is being/continued to be used in production. I think Freshcom was being used in prod at some point or was about to launch. The author is here in the forum @rbao.

If you search the forum you have more questions like yours:

• Resources for building an e-commerce store in Phoenix?
• Presenting Aviacommerce, open source e-commerce in Elixir

• https://learn-elixir.dev/blogs/avoiding-data-loss-with-elixir-dets

defmodule Mixer.Persist do
  use GenServer

  @table_name :mixer_persist

  def start_link(table_name) do
    GenServer.start_link(__MODULE__, table_name, name: __MODULE__)
  end

  def init(table_name) do
    {:ok, _} = :dets.open_file(table_name || @table_name, [])
  end

  def get(table_name \\ @table_name, key) do
    case :dets.lookup(table_name, key) do
      [{^key, value}] -> value
      [] -> nil
    end
  end

  def set(table_name \\ @table_name, key, value) do
    :dets.insert(table_name, {key, value}) && value
  end

  def get_or_set(table_name \\ @table_name, key, fun) when is_function(fun) do
    get(table_name, key) || set(table_name, key, fun.())
  end
end

Example Makefile for a thin elixir app.

app := next

default: s
b:
        mix do deps.get, deps.compile, compile
s:
        iex -S mix
t:
        mix test
tl:
        mix test --listen-on-stdin
u:
        cat Makefile
r:
        MIX_ENV=prod mix release --path=~/${app}/

Example Makefile for an Elixir/Phoenix webapp

port := 4030
prod-env := DATABASE_URL=ecto://postgres:postgres@localhost:5432/my-app MIX_ENV=prod SECRET_KEY_BASE=8X3vyc0qkLs38OFTa4C+ZTx6Q9h0KXyfh8Ug/Yt4IUnSv8WQSzuDDe7OiR5iGwDK PHX_SERVER=true PHX_HOST=localhost PORT=${port}
cmd := $$MAKE_CMD

default: start-prod
cmd:
        echo ${cmd}
# Example usage
#
# MAKE_CMD="mix ecto.create" make -s prod-exec
#

# Start in production env
prod-exec:
        ${prod-env} ${cmd}

start-prod:
        ${prod-env} iex -S mix phx.server

# Development
build:
        mix do deps.get, deps.compile, compile
start: build
        iex -S mix phx.server
assets:
        mix assets.setup
release:
        mix deps.get --only prod
        MIX_ENV=prod mix compile
        MIX_ENV=prod mix assets.deploy
        MIX_ENV=prod PHX_SERVER=true mix release --path ~/my-app --overwrite 
release-start:
        ${prod-env} ~/my-app/bin/my-app start

How to use IO.inspect on a long list without trimming it? See Inspect.Opts for a description of the available options, but in short:

IO.inspect(list, limit: :infinity)

• Discover Livebook notebooks (Elixir)
• https://github.com/aslakjohansen/livebook-demos
• https://github.com/Arp-G/async-elixir
• https://github.com/whatyouhide/guide_async_processing_in_elixir

ffmpeg -i infile.mp4 -vn -acodec copy outfile.ogg

Extract a single frame at time 10s (also consider using accurate_seek argument).

ffmpeg -i vid.mp4 -ss 10 -frames:v 1 thumb.png

Extract a frame each minute.

ffmpeg -i vid.mp4 -vf fps=1/60 thumb%03d.png

Extract list of specific frames using ffmpeg. More details in this StackOverflow thread.

ffmpeg -i in.mp4 -vf select='eq(n\,100)+eq(n\,184)+eq(n\,213)' -vsync 0 frames%d.jpg

FFmpeg is primarily a processor of timed video i.e. media with a cycle rate such as framerate or sample rate. It assumes that the output should be at the same rate as the source. If inadequate frames are supplied, it duplicates unless told not to. -vsync 0 is added which, in this case, tells it to suppress duplication.

Using FFMPEG's scene detection to generate a visual shot summary of Television News.

time ./ffmpeg -i ./VIDEO.mp4 -vf "select=gt(scene\,0.4),scale=160:-1,tile=6x80" -frames:v 1 -qscale:v 3 preview.jpg  

ffmpeg -ss 10 -t 20 -i infile.wav outfule.wav

Another example using timing

ffmpeg -ss 00:00:15.00 -i in.mp4 -t 00:00:10.00 -c copy out.mp4

If we want our volume to be half of the input volume:

ffmpeg -i input.wav -filter:a "volume=0.5" output.wav

150% of current volume:

ffmpeg -i input.wav -filter:a "volume=1.5" output.wav

You can also use decibel measures. To increase the volume by 10dB:

ffmpeg -i input.wav -filter:a "volume=10dB" output.wav

For more details refer this StackOverlow thread.

Fade in from second 0 to 5.

ffmpeg -i input.mp4 -af afade=in:0:d=5 output.mp4

The filter works by changing the presentation timestamp (PTS) of each video frame. For example, if there are two succesive frames shown at timestamps 1 and 2, and you want to speed up the video, those timestamps need to become 0.5 and 1, respectively. Thus, we have to multiply them by 0.5.

To double the speed of the video, you can use:

ffmpeg -i input.mkv -filter:v "setpts=0.5*PTS" output.mkv

To slow down your video, you have to use a multiplier greater than 1:

ffmpeg -i input.mkv -filter:v "setpts=2.0*PTS" output.mkv

For audio I found this

ffmpeg -i input.wav -filter:a "atempo=0.75" output.mp3 

ffmpeg -f concat -i list-of-files.txt -c copy outfile.wav

The list-of-files.txt should be something like this:

file './infile.wav'
file './infile.wav'
file './infile.wav'
file './infile.wav'
file './infile.wav'
file './infile.wav'

N.B. you could see the error 'Unsafe filename..Operation not permitted'; as reported in this SO thread you could solve this issue by using single quotes in the list of filenames, avoiding any ~ or other "strange" chars.

Basic ffmpeg scene detection:

ffmpeg -i input.flv -filter:v "select='gt(scene,0.4)',showinfo" -f null -
# or
ffmpeg -i in.mp4 -vf "select='gte(scene,0.4)',metadata=print:file=scenescores.txt" -an -f null -

scene (video only) value between 0 and 1 to indicate a new scene; a low value reflects a low probability for the current frame to introduce a new scene, while a higher value means the current frame is more likely to be one (see the example below) https://ffmpeg.org/ffmpeg-filters.html#select_002c-aselect. Set the scene change detection threshold as a percentage of maximum change on the luma plane. Good values are in the [8.0, 14.0] range. Scene change detection is only relevant in case combmatch=sc. The range for scthresh is [0.0, 100.0]. https://ffmpeg.org/ffmpeg-filters.html

• Scenecut Extractor (python)
• PySceneDetect
• FFMPEG Ticket
• SCENE CHANGE DETECTION FOR H.264 USING DYNAMIC THRESHOLD TECHNIQUES

Converts a.wav to MPEG audio at 22050 Hz sample rate.

ffmpeg -i /tmp/a.wav -ar 22050 /tmp/a.mp2

You can follow this gist.

ffmpeg -i file.mp3 -metadata title="Track Title" -metadata artist="The artist" -metadata album="Album name" out.mp3

Taken from FFMPEG doc

Ref. https://docs.github.com/en/authentication/managing-commit-signature-verification/generating-a-new-gpg-key

Remember to execute in a terminal capable of reading password via ncurses-like input method.

gpg --full-generate-key

Ref. https://docs.github.com/en/authentication/managing-commit-signature-verification/adding-a-new-gpg-key-to-your-github-account

From the list of GPG keys, copy the long form of the GPG key ID you'd like to use. In this example, the GPG key ID is 3AA5C34371567BD2:

$ gpg --list-secret-keys --keyid-format=long

This will output something like

/Users/hubot/.gnupg/secring.gpg
------------------------------------
sec   4096R/3AA5C34371567BD2 2016-03-10 [expires: 2017-03-10]
uid                          Hubot
ssb   4096R/42B317FD4BA89E7A 2016-03-10

Paste the text below, substituting in the GPG key ID you'd like to use. In this example, the GPG key ID is 3AA5C34371567BD2:

$ gpg --armor --export 3AA5C34371567BD2

Copy your GPG key, beginning with –—BEGIN PGP PUBLIC KEY BLOCK–— and ending with –—END PGP PUBLIC KEY BLOCK–—.

Ref. https://docs.github.com/en/authentication/managing-commit-signature-verification/telling-git-about-your-signing-key

Use the gpg --list-secret-keys --keyid-format=long command to list the long form of the GPG keys for which you have both a public and private key. A private key is required for signing commits or tags (same ID as for Upload to Github). Then:

git config --global user.signingkey 3AA5C34371567BD2

Ref. https://unix.stackexchange.com/questions/481939/how-to-export-a-gpg-private-key-and-public-key-to-a-file

Interesting resources if you encounter problems:

• https://gist.github.com/paolocarrasco/18ca8fe6e63490ae1be23e84a7039374

If every gpg command goes timeout with a message like gpg: Nota: database_open 134217901 waiting for lock (held by 31477) you could try to solve via:

rm -rf ~/.gnupg/*.lock
rm -rf ~/.gnupg/public-keys.d/*.lock

From GitHub docs:

ssh-keygen -t ed25519 -C "your_email@example.com"

Most of info taken from this page.

If you want to add a text stripe under the image

convert original-image.jpg -background Khaki -font Arial -pointsize 27 label:'Sfilatini Buitoni' -gravity Center -append out-image.jpg 

You can also use a remote image, like

display -size 1920x1080 -window root /path/to/image.jpg

Retrive information of device through

udevadm info --attribute-walk --name /dev/input/mouse0

Then add a rule in etc/udev/rules.d

SUBSYSTEM=="input", KERNEL=="mouse0", OWNER="myusername"

Configuring The VNC Server

As it turns out, the pcDuino comes with the x11vnc server already installed and all that’s necessary is to configure SSH on the pcDuino and local machine to support it. (Note: while working on putting together a bootable SD card I found out this is not necessarily the case. If you find the x11vnc server is not installed, you can do so by executing the command from the pcDuino command line.)

sudo apt-get install x11vnc

On the local machine and change to the /etc/ssh directory as root:

sudo su
cd /etc/ssh

Open the file ssh_config file in your editor of choice and find the ForwardX11 option. Uncomment it if necessary, change its value to YES, and save the file.

Now log into the pcDuino via the SSH link and gain root access in the same manner:

sudo su
cd /etc/ssh

Open the file sshd_config file in your editor of choice, find the X11Forwarding option, change its value to YES, and save the file.

Install and Connect Via a VNC Client

The final step is to install a VNC client on your local computer. There are a number of them to choose from. Of these, I chose xtightvncviewer for no other reason than it was there, installing it as:

sudo apt-get install xtightvncviewer

Putting It All Together

At this point if you SSH into the pcDuino and try to start the VNC server, you’ll get an error indicating you cannot connect to the display (XOpenDisplay failed) along with hints on how to fix it. The cause of this error is that the account used for SSH does not have sufficient permissions to connect to the X display.

To fix this, execute the command ps -fe | grep usr/bin/X | grep -v grep from the pcDuino command line. The returned process will have have an -auth flag. Take note of the associated file. On my machine, it was /var/run/lightdm/root:0.

Exit from the SSH session and reconnect to the pcDuino using the command

ssh -L 5900:localhost:5900 <user>@<pcDuino_ip_address> ‘sudo x11vnc -auth <path_to_authority_file>’ -display :0

where <path_{toauthorityfile}> is the file associated with the -auth flag noted above. This will log you into the pcDuino via SSH and start an instance of the X server. You can then start the VNC viewer from the local machine command line with the command:

vncviewer localhost:5900 &

To see all the files the package installed onto your system, do this:

dpkg-query -L <package_name>

To see the files a .deb file will install

dpkg-deb -c <package_name.deb>

Add a file in /usr/share/xsessions/ with something like this (example for i3)

[Desktop Entry]
Name=i3
Comment=improved dynamic tiling window manager
Exec=i3
TryExec=i3
Type=Application
X-LightDM-DesktopName=i3
DesktopNames=i3
Keywords=tiling;wm;windowmanager;window;manager;

In ~/.local/share/applications/ or ~/.config/autostart to start at login.

[Desktop Entry]
Type=Application
Name=Clock
Exec=/usr/bin/python3 /home/pi/clock.py

xset s off (turns off the screen saver) xset s noblank (turns off blanking) xset -dpms (disable the power management)

Here's a StackOverlow thread: from Linux 4.20 cat /sys/class/power_supply/BAT1/status; check the link for old methods.

Iptables rules used to configure a router on linux

WAN='wlp7s0'
LAN='enp7s0'

iptables -F
iptables -P INPUT DROP
iptables -P OUTPUT ACCEPT
iptables -P FORWARD ACCEPT

iptables -A INPUT -m state --state=RELATED,ESTABLISHED -j ACCEPT
iptables -A INPUT -i $LAN -j ACCEPT

# iptables -A FORWARD -m state --state=RELATED,ESTABLISHED -j ACCEPT

iptables -t nat -F
# iptables -t nat -A POSTROUTING -s 172.16.0.0/20 -o $WAN -j MASQUERADE
iptables -t nat -A POSTROUTING -o $WAN -j MASQUERADE

Here's a good blogpost specific for Raspberry PI.

If you're using the LightDM and you want to set monitor resolutions and layout at the startup, edit the display-setup-script option in /etc/lightdm/lightdm.conf.

You can use feh

feh --bg-fill ~/path/to/image.png

Or you can use the xsetroot utility (usually packaged into xdotool). Consider xsetroot accepts a particular format of file called bitmap (xsetroot -bitmap bitmap-file.xbm); to convert a file into this format you can use Imagemagick. N.B. the bitmap is not the well-known Windows bitmap format (.bmp) but is the X11 bitmap format (.xbm):

convert wallpaper.png wallpaper.xbm

If the app as been built as GTK+ app it accepts --screen, --name, --class options. It can be used, for instance, by i3 rules configuration.

To get the window ID use xdotool (ex. xdotool search -class mpv)

There are many options.

• You can use the Emacs for Mac OS X bundle, but it is not always up to date to newer versions.
• You can install via homebrew
• You can install the Emacs plus via homebrew

brew tap d12frosted/emacs-plus
brew install emacs-plus
# or
brew install emacs-plus@29 

Taken from this article.

sudo dscacheutil -flushcache
sudo killall -HUP mDNSResponder

Taken from this Osx Daily post. ⚠️ it seems not working on my Mac 🤔

defaults write com.apple.QuickTimePlayerX MGPlayMovieOnOpen 1

For wireless: Use ipconfig getifaddr en1. For ethernet: Useipconfig ipconfig getifaddr en0. For public IP address: dig -4 TXT +short o-o.myaddr.l.google.com @ns1.google.com.

• https://pi3g.com/enabling-and-checking-i2c-on-the-raspberry-pi-using-the-command-line-for-your-own-scripts/

• https://forums.raspberrypi.com/viewtopic.php?t=116174
• https://github.com/bsteinsbo/rpi_touch_driver

sudo apt-get update && sudo apt-get install erlang erlang-dev elixir

or if you want to automate via Makefile

raspi-setup:
        sudo apt update
        sudo apt install tmux emacs
        sudo apt install erlang erlang-dev elixir

• https://www.freva.com/connecting-a-fan-to-a-raspberry-pi/?srsltid=AfmBOorgZc90NP9RgfctZKWpl-V6XJtozQjo7NU8pU_Lr1S_9rTWGVJv

Use motion app; Here's a detailed article: How to Make Raspberry Pi Webcam Server and Stream.

I want to use the mic of the Raspberry to stream on the audio over the network. I've achieved by following the instructions in this blogpost: Stream audio over the network using VLC. To detect the alsa card for recording use arecord -l

card 3: Device [USB PnP Sound Device], device 0: USB Audio [USB Audio]
  Subdevices: 1/1
  Subdevice #0: subdevice #0

then stream using VLC

cvlc -vvv alsa://plughw:3 --sout '#transcode{acodec=mp3,ab=64,channels=1}:standard{access=http,dst=0.0.0.0:8888/out.mp3}'

Connect to the raspberry: if the IP address is, for instance, 192.168.1.44, go to http://192.168.1.44:8888/out.mp3.

If you're not interested in streaming but just record the audio onto a file start recording using arecord for 4 seconds in dat format (16bit; see man for more options):

arecord -d 4 -f dat spy.wav

Other resources:

• https://community.element14.com/challenges-projects/project14/spynerd/b/blog/posts/pi-spy-audio-recorder---part-1

https://raspberrytips.com/access-point-setup-raspberry-pi/

Add a service to systemd (more info here, while here's an article on how to create and manage user’s services With systemd).

Create /lib/systemd/system/blink.service (or /lib/systemd/user/blink.service in case of user-space app) with

[Unit]
Description=Blink my LED
After=multi-user.target

[Service]
Environment="MY_SHELL_ENV_VAR=value"
ExecStart=/usr/bin/python3 /home/pi/blink.py

[Install]
WantedBy=multi-user.target

Then start with systemctl [--user] (enable|restart|start|stop) blink

To start a service after a specific timeout (ex. 30 seconds) add:

[Service]
ExecStartPre=/bin/sleep 30

Clear journalctl: the self maintenance method is to vacuum the logs by size or time. Retain only the past two days:

journalctl --vacuum-time=2d

or retain only the past 500 MB

journalctl --vacuum-size=500M

To print last 40 entries for a particular service (i.e. unit) and keeps following the logs:

journalctl -n 40 -u my-service -f

Sometimes you end up by having some services to start and immediately stop (for instance my-daemon.service Deactivated successfully). I've found the solution to in this StackOverlow thread: you have to specify the Type!

Use dockage/tor-privoxy:latest image or dperson/torproxy

sudo docker run -it -p 8118:8118 -p 9050:9050 -d dperson/torproxy

then verify you're using the tor proxy connecting to https://check.torproject.org/

curl -Lx http://localhost:8118 https://check.torproject.org/ | grep "Congratulations"

More details in this StackOverflow thread showing different approaches, here I'm reporting just one.

// @grant        GM_download

function saveData(data, filename) {
    const blob = new Blob([data], { type: "text/plain" });
    const url = URL.createObjectURL(blob);
    GM_download({
	  url: url,
	  name: filename,
	  saveAs: false,
    });
}

saveData("hello world", "hello.txt");

Go the "Manage subscription" page, open the Web Inspector of the browser and execute the snippet below in the JS console; N.B. ensure you've loaded all the entries by scrolling down to the very end of the page.

var channelList = [];
[...document.querySelectorAll('a#main-link.channel-link')].forEach(el => {
  const channelId = el.getAttribute("href");
  channelList.push((`https://www.youtube.com${channelId}`));
});
console.log(channelList.join("\n"));

Get the Channel ID of a Youtube channel (manual approach): here a video explaining how to do that. You can ease the process using by copy/pasting this snippet into the Dev console (if the browser allows you that)

alert(document.querySelector("link[itemprop='url']").href);

then construct as follow:

https://youtube.com/watch?v=CHANNEL-ID to https://www.youtube.com/feeds/videos.xml?channel_id=CHANNEL-ID

I made some experiments to automate this process:

• a sample NodeJS project (see this section)
• using ad-hoc Emacs function