Local Port Forwarding​

ssh -L [client_port]:[host_to_forward]:[host_to_forward_port]

Suppose there is a client A, an SSH server B, and a host C, and you want to forward C:8080 to port 80 on A.

ssh -L80:C:8080 B

With this forwarding, accessing http://localhost from A will display the same content as http://C:8080 on B.

In summary, even if C is not visible from A, you can access the home network via SSH if port 22 is open to the outside. If B is visible from A, you can forward C's port to A via B.

Using -g allows access to C:8080 from computers on A's network using A's hostname.

Remote Port Forwarding​

ssh -R [client_port]:[host_to_forward]:[host_to_forward_port]

Unlike local forwarding, it forwards ports visible from the client instead of ports visible from the destination.

Suppose there is a client B, an SSH server A, and a host C, and you want to forward C:8080 to port 80 on A.

ssh -R80:C:8080 A

With this forwarding, accessing http://localhost from A will display the same content as http://C:8080 on B.

Even if B is not accessible from the outside, if a connection between B and A is established, you can forward the content of C to A. It is often used when you cannot directly operate B. When a connection between B and A is broken, tools like auto-ssh are often used to automatically reconnect.

Go Installation​

Install Go to install powerline-go.

brew install go

Powerline-go Installation​

go get -u github.com/justjanne/powerline-go

Configuration

Bashrc​

Open ~/ .bashrc with Vim or nano and add the following.

GOPATH=$HOME/go
function _update_ps1() {
   PS1="$( $GOPATH/bin/powerline-go -newline -error $? )"
}
if [ "$TERM" != "linux" ] && [ -f "$GOPATH/bin/powerline-go" ]; then
   PROMPT_COMMAND="_update_ps1; $PROMPT_COMMAND"
fi

Run source ~/.bashrc to apply the changes.

Font

This should finish it, but there might be character encoding issues. You need to set a font that corresponds to Powerline. On Windows, you can use Cascadia Code PL or Cascadia Mono PL.

We recommend PlemolJP from https://github.com/yuru7/PlemolJP/. Download it from https://github.com/yuru7/PlemolJP/releases, click on PlemolJP_NF_vX.X.X.zip, download, extract, and install the font. Set the font to PlemolJP35 Console NF.

Using delay() in Arduino prevents any other actions from being performed during the waiting time. I created a program that blinks an LED with a 1-second cycle using millis().

1. Get the time using millis() and divide it by the interval, assigning the result to t.
2. Compare the previous t and the new t and execute a function if they are different.

Example

unsigned long t = 0, ot;

void sетуp(){
  pinMode(LED_BUILTIN, OUTPUT);
}

void loop() {
  ot = t;
  t = millis() / 500;
  if(ot != t){
    if(t % 2){
      digitalWrite(LED_BUILTIN, LOW);
    }else{
      digitalWrite(LED_BUILTIN, HIGH);
    }
  }
}

This guide explains how to set up a Raspberry Pi without needing a monitor.

• Requires a Raspberry Pi device that can connect an Ethernet cable for a wired connection.
• A computer is needed to operate the Raspberry Pi.

Install Raspberry Pi Imager, select the OS. Choose the micro SD card to write to, and click WRITE.

Configuration

Enable SSH​

Enabling SSH allows you to operate the Raspberry Pi remotely.

Reinsert the micro SD card and create a text file named ssh directly in the root directory. No extension is needed.

Enable VNC​

Open config.txt and uncomment and save the following lines:

framebuffer_width=1280
framebuffer_height=720

Boot Up​

Insert the micro SD card into the Raspberry Pi, connect the power, and boot it up.

Connect via SSH​

Connect using hostname raspberrypi, username pi, and password raspberry.

Update Packages​

sudo apt update
sudo apt upgrade -y

Enable VNC​

sudo raspi-config

Select 3 Interface Options, then P3 VNC, and select YES. Close with Finish.

Connect via VNC​

Use the same username and password as for SSH.

Enable Wi-Fi​

Enabling Wi-Fi via VNC eliminates the need for a wired connection, allowing you to operate the Raspberry Pi with only power.

When executing CGI in the browser, an error occurs stating: /usr/bin/env: 'ruby': No such file or directory

#!/usr/bin/env ruby

# ...

Cause

The $PATH is not set.

#!/usr/bin/env bash

echo -ne "Content-type: text/html\n\n"
echo $PATH

Running this will display:

/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin

This shows that the directory containing Ruby is not present.

Solution

Set the Ruby path using :CGIPathEnv.

srv = WEBrick::HTTPServer.new({
   :DocumentRoot => "./site/",
   :Port => 8080,
   :CGIPathEnv => ENV["PATH"]
})

Creating a Template​

bundle gem <GEM Name> -t
cd <GEM Name>

Editing the Gemspec​

0. Open <GEM Name>.gemspec.
1. Edit spec.summary, spec.description, spec.homepage,
2. Write the homepage URL to spec.metadata["allowed_push_host"]
3. Write the Gem's page to spec.homepage
4. Write the repository URL to spec.metadata["source_code_uri"]
5. Write the URL of changelog.md to spec.metadata["changelog_uri"]

Set at least this much.

Push to GitHub and Install​

git init
git add .
git commit -m First Commit
git remote add origin [email protected]:<username>/<GEM Name>.git
git push -u origin master

Install​

gem install specific_instal
gem specific_install -l "git://github.com/<username>/<GEM Name>.git"

Gemfile​

gem "<GEM Name>", github: "<username>/<GEM Name>.git", branch: :main

Introducing the tiv command for displaying images in the terminal.

It's convenient when you don't want to open a file explorer.

git clone https://github.com/stefanhaustein/TerminalImageViewer.git
cd TerminalImageViewer/src/main/cpp
make -j
sudo make install

An attempt to apply a bilateral filter using ImageMagick. For installation instructions for ImageMagick, see install-magick.html

magick convert Parrots.jpg -bilateral-blur 10x10 output.png

Results

• Input image

  

• Output image

  

0. Let C be the remainder when A is divided by B.

1. Let D be the remainder when B is divided by C.

2. Let E be the remainder when C is divided by D.

   ...

3. Let Y be the remainder when X is divided by 0.

   Then Y is the greatest common divisor.

Bash Script

#!/usr/bin/env bash

function gcd(){
   test $2 -eq 0 && echo $1 || gcd $2 $(( $1 % $2 ))
}

gcd 1071 1029
# 21

wget https://download.imagemagick.org/ImageMagick/download/ImageMagick-7.0.11-14.tar.xz

Extract

tar xf ImageMagick-7.0.11-14.tar.xz

Make

sudo apt update
cd ImageMagick-7.0.11-14.tar.xz
./configure
make -j
sudo make install
sudo ldconfig /usr/local/lib