Jekyll2026-07-05T14:32:42+00:00https://linda-jansson.com/feed.xmllinjan2 Sysadmin NotebookTechnical notes, cheat sheets, and occasional web experimentsLinda JanssonJekyll site setup2026-04-06T00:00:00+00:002026-04-06T00:00:00+00:00https://linda-jansson.com/jekyll-site-setupJekyll site setup

Setup a Jekyll static site generator with the Minima theme for blog posts.

Jekyll installation

See Jekyll installation instructions for other Linux.

# install ruby with dependencies
sudo dnf install --setopt install_weak_deps=0 \
  ruby ruby-devel openssl-devel redhat-rpm-config gcc-c++ @development-tools \
  libffi-devel libyaml-devel
  # NOTE: these ruby packages install gems into `/usr/share/gems`

# configure gem to install binaries into a proper user folder
echo 'gem: --no-document --bindir ~/.local/share/gem/ruby/bin' > ~/.gemrc
# add gem bin path to PATH
export PATH="$(gem env user_gemhome)/bin:${PATH}"

# install jekyll and bundler
gem --version
gem install jekyll bundler

Persist the updated PATH variable for gem binaries in ~/.bashrc.

cat >> ~/.bashrc <<'
if command -v gem &>/dev/null
then
  GEM_HOME="$(gem env user_gemhome)"
  if ! [[ "$PATH" =~ "${GEM_HOME}/bin" ]]
  then
    PATH="${GEM_HOME}/bin:${PATH}"
  fi
fi
export PATH
'

Configure Jekyll site

Generate a site.

  • Do not run bundle install/bundle update before configuring project local gem location to ./vendor/bundle.
  • By default a new Jekyll site uses Minima v2 theme gem, which we change to Minima v3 using the “remote theme” plugin.
  • Replace all fixed gem x.y.z versions in Gemfile to x.y in order to get latest versions.
jekyll new . --skip-bundle
  # _config.yml
  # _posts/
  # index.markdown
  # about.markdown
  # 404.html
  # Gemfile
  # .gitignore

# configure bundler to install gems into project folder
bundle config set --local path 'vendor/bundle'

Clear the Gemfile in order to install latest gem versions. Manually remove directives related to Windows and JRuby.

# remove packages with fixed versions added by default
bundle remove --skip-install minima
bundle remove --skip-install jekyll-feed
bundle remove --skip-install jekyll

bundle add --skip-install jekyll

bundle add --skip-install \
  --group jekyll_plugins \
  jekyll-remote-theme \
  jekyll-feed \
  jekyll-seo-tag \
  jekyll-minifier

Remove all patch versions in the Gemfile. It should look like this:

source "https://rubygems.org"

gem "jekyll", "~> 4.4"

gem "jekyll-remote-theme", "~> 0.4", group: :jekyll_plugins
gem "jekyll-feed", "~> 0.17", group: :jekyll_plugins
gem "jekyll-seo-tag", "~> 2.8", group: :jekyll_plugins
gem "jekyll-minifier", "~> 0.2", group: :jekyll_plugins

# remove Gemfile.lock in order to update to latest gem package versions
rm Gemfile.lock
# update gem versions
bundle update --all
bundle install
# clean up unused gems
bundle clean  # project local
gem clean     # user installed gems

Edit _config.yml to configure the site. The variables in _config.yml will be accessible in the templates via {{ site.myvariable }} (e.g. {{ site.author.name }}).

# _config.yml
title: My Jekyll site
author:
  name: linjan2
  email:
description: >-
  Site description that will appear in document head meta and in feed.xml
  site description.
url: https://linda-jansson.com
baseurl: "" # the subpath of your site, e.g. /blog, if served from subpath

# Replace "theme: minima" with remote_theme
remote_theme: jekyll/minima@bf9ef98 # static ref for Minima v3
  # See docs at: https://github.com/jekyll/minima/tree/master

plugins:
  - jekyll-remote-theme
  - jekyll-feed
  - jekyll-minifier
  - jekyll-seo-tag

# Exclude files from processing (in addition to the default jekyll excludes)
exclude:
  - tmp

minima:
  skin: auto

jekyll-minifier:
  exclude: []

# test by serving on http://localhost:4000
bundle exec jekyll serve

# build the generated website into _site/
export JEKYLL_ENV=production # required to activate things like jekyll-minifier
bundle exec jekyll build

Commit the site files to Git repository.

echo 'tmp/' >> .gitignore
echo '.bundle/' >> .gitignore
git init . && git add . && git commit 'initial commit'

Add more custom site files

A Jekyll theme utilizes a folder structure to define the posts, layouts, and includes. Make custom additions by adding files to local project folder. Files in local project folder override those pre-defined in the theme.

./
├── assets/
│   ├── about.svg
│   ├── css/
│   │   └── custom.css
│   ├── index.svg
│   └── jekyll-example/
│       ├── index.js
│       └── style.css
├── _config.yml
├── _drafts/
├── favicon.ico
├── Gemfile
├── Gemfile.lock
├── _includes/
│   ├── custom-head.html
│   └── sub-footer.html
├── index.md
├── pages/
│   ├── 404.md
│   ├── about.md
│   └── categories.md
└── _posts/
    ├── 2026-04-08-jekyll-example-html-post.html
    └── 2026-04-06-jekyll-example-post.md

Update the _config.yml to add more configurations.

# ...

minima:
  # ...
  nav_pages: # Update the navigation pane with specific site pages
    - pages/categories.md
    - pages/about.md
  date_format: "%b %-d, %Y"
  social_links:
    - title: GitHub
      icon: github
      url: https://github.com/linjan2

disqus:
  shortname: linda-jansson-com

# set defaults for front matter variables
defaults:
  # for all files
  - scope:
      path: '' # matches all
    values:
      author: Linda Jansson
  # for all files under _posts/
  - scope:
      path: _posts
      type: posts
    values:
      layout: post
      permalink: /:title/
  # for all files under _pages/
  - scope:
      path: pages
    values:
      layout: page
      comments: false # don't display disqus

Create a custom “404 Not found” page.

<!-- pages/404.md -->
---
layout: page
title: 404 - Page Not Found
permalink: /404.html
---

Sorry, we couldn't find the page you're looking for.

[← Back to Home](/)

Create an “about” page. The liquid templating language is used to insert a SVG file fron static_files variables, which holds all “static” site files that don’t have a front matter.

<!-- pages/about.md -->
---
layout: page
title: About
permalink: /about/
---


{% assign file = site.static_files | where: "name", "about.svg" | first %}
<img
  src="{{ file.path }}"
  title="Flower image"
  alt="Image of a pink flower"
  height="100px"
  style="display: block; margin-left: auto; margin-right: 0;"
/>

Create a page to display all post categories with links.

<!-- pages/categories.md -->
---
layout: page
permalink: /categories/
title: Categories
---


<div id="archives">
{% assign sorted_categories = site.categories | sort %}
{% for category in sorted_categories %}
  <div class="archive-group">
    {% capture category_name %}{{ category | first }}{% endcapture %}
    <div id="{{ category_name | slugize }}"></div>
    <h3 class="category-head">{{ category_name }}</h3>
    <a name="{{ category_name | slugize }}"></a>
    {% for post in site.categories[category_name] %}
    <article class="archive-item">
      <h4><a href="{{ site.baseurl }}{{ post.url }}">{{ post.title }}</a></h4>
    </article>
    {% endfor %}
  </div>
{% endfor %}
</div>

Override the Minima theme’s custom head _includes/custom-head.html to include CSS assets (one common custom.css and then a loop to include from a variable named css that can be set in a file’s front matter).

<!-- _includes/custom-head.html -->

<link rel="stylesheet" href="/assets/css/custom.css">
{%- for css in page.css -%}
  <link rel="stylesheet" href="{{ css | relative_url }}">
{%- endfor -%}

Override the Minima theme’s custom sub-footer (i.e. before end of body closing tag) _includes/sub-footer.html to include JavaScript assets (from variable set in front matter).

<!-- _includes/sub-footer.html -->

{%- for js in page.js -%}
  <script src="{{ js | relative_url }}"></script>
{%- endfor -%}

Create posts

Jekyll posts must be named YEAR-MONTH-DAY-title.MARKUP. Create the post files under _posts/. Drafts can be created under _drafts.

Create a markdown post:

cat > "_posts/$(date +%F)-jekyll-example-post.md" <<<'---
title: Jekyll example post
categories: cheatsheet
---

# Jekyll example post

This is an example post.
'

Create an HTML post that avoids template interpretation. Add variables js and css in front matter to make the head and sub-footer in _includes/ insert them as CSS/JS includes.

cat > "_posts/$(date +%F)-jekyll-example-html-post.html" <<<'---
title: Jekyll example HTML post
js:
  - https://unpkg.com/petite-vue@0.4.1/dist/petite-vue.iife.js
  - /assets/jekyll-example/index.js
css:
  - /assets/jekyll-example/style.css
categories: example
---

<!-- avoid excerpt separator \n\n -->

{% raw %}

<h1>Jekyll example HTML post</h1>

{% endraw %}
'
]]>Linda JanssonGLSL editor2025-11-14T00:00:00+00:002025-11-14T00:00:00+00:00https://linda-jansson.com/glsl-editor
Browser doesn't support HTML5 canvas.

Vertex shader:

#version 100
uniform float u_rotate;
uniform vec4 u_color;
uniform vec2 u_aspect;
uniform vec2 u_mouse;
uniform float u_time;

attribute vec2 position;
attribute vec2 texel;

varying vec4 color;
varying vec2 st;
//varying float time;

void main() {
  gl_PointSize = 5.0;

  vec2 p = position * u_aspect * 2.0 - 1.0; // aspect is inverted; x,y on [-1, 1]

  vec2 u = vec2(1.0, u_rotate);
  vec2 z = vec2(1.0-u_rotate*u_rotate, 2.0*u_rotate) / dot(u,u);
  // complex multiplication z*p (mat2 is column-major)
  // p = vec2(z.x*position.x - z.y*position.y, z.x*position.y + z.y*position.x);
  mat2 rot = mat2(z.x, z.y, -z.y, z.x);

  gl_Position = vec4(rot*p, -1.0, 1.0);

  color = u_color;
  st = vec2(texel.x, 1.0-texel.y); // s & t on [0,1]
  //time = u_time;
}

Fragment shader:

#version 100
precision mediump float;
uniform sampler2D u_sampler;
uniform vec2 u_dimensions;
varying vec4 color;
varying vec2 st;
// varying vec2 time;

void main() {
  vec2 p = gl_FragCoord.xy * u_dimensions;
  gl_FragColor = vec4(p, 1.0, 1.0);

  // gl_FragColor = color;
  // gl_FragColor = texture2D(u_sampler, st);
}
]]>Linda JanssonGuess the word2025-11-14T00:00:00+00:002025-11-14T00:00:00+00:00https://linda-jansson.com/guess-the-word
Guess the word! Kind of like Wordle. Correctly placed letters are shown in green and bold. Letters that occur in the word, but are not correctly placed are shown in purple and italic. The guess must fill all letters of the word, but doesn't have to be a valid dictionary word. Guess as many times as you want.
{{c.l}}
{{input[n-1] || '.'}}

{{definition.word}}
{{definition.text}}
—{{definition.attributionText}}

]]>Linda JanssonSpin the wheel2025-11-14T00:00:00+00:002025-11-14T00:00:00+00:00https://linda-jansson.com/spin-the-wheel

Select items for the wheel

Pressing the button spins the wheel.
{{item.text}}

Results

  • ...
  • {{items2.length - i}}. {{item}}
]]>Linda JanssonCamera tethering on Linux2024-11-10T00:00:00+00:002024-11-10T00:00:00+00:00https://linda-jansson.com/camera-tethering-on-linuxCamera tethering on Linux

Install gphoto2.

sudo dnf install gphoto2
man gphoto2

# show settings
cat ~/.gphoto/settings

# various options
gphoto2 --list-config
gphoto2 --get-config shutterspeed
gphoto2 --get-config capturetarget
# only use camera RAM for storing images (not SD card)
gphoto2 --set-config capturetarget=0

# list the auto-detected cameras
gphoto2 --auto-detect
gphoto2 --summary
gphoto2 --list-files
gphoto2 --get-all-files

Create the script gphoto-hook.sh as below. It’s the hook that is run when a photo is taken.

#!/bin/sh
case "${ACTION}" in
  start)
  ;;
  download)
    echo "Downloaded image ${PWD}/${ACTION}"
  ;;
esac

Start tethering.

# tether and capture camera shots
gphoto2 --capture-tethered --hook-script=./gphoto-hook.sh
  # if multiple devices are detected use e.g. --camera='Sony Alpha-A6000'

# capture and save on SD card
gphoto2 --capture-image

# capture and save on SD card, download to computer, then delete from camera
gphoto2 --capture-image-and-download --filename %Y%m%d%H%M%S.arw
]]>Linda JanssonCreate Android Virtual Devices (AVD)2024-11-02T00:00:00+00:002024-11-02T00:00:00+00:00https://linda-jansson.com/create-android-virtual-devices-(avd)Create Android Virtual Devices (AVD)

The AVD Manager CLI tool avdmanager is included in the Android SDK command-line tools package.

The SDK manager tool sdkmanager installs and updates packages. First download the latest version of “Command line tools only” .zip file from https://developer.android.com/studio#command-line-tools-only. Then use sdkmanager to reinstall cmdline-tools as a package in an appropriate location.

mkdir -p /path/to/sdk/

unzip commandlinetools-linux-11076708_latest.zip
cmdline-tools/bin/sdkmanager --sdk_root=/path/to/sdk 'cmdline-tools;latest'

export "PATH=${PATH}:/path/to/sdk/cmdline-tools/latest/bin"

sdkmanager --list_installed

Use avdmanager to create virtual device. A system image and the emulator must be installed first.

sdkmanager --list | grep system-images
# install the emulator, a system image (with play store),
# an SDK platform, and the platform tools
sdkmanager emulator \
  'system-images;android-35;google_apis_playstore;x86_64' \
  'platforms;android-35' \
  platform-tools

# list device definitions (e.g. pixel_8)
avdmanager list device --compact

avdmanager create avd --name pixel8_api35 \
  --package 'system-images;android-35;google_apis_playstore;x86_64' \
  --device pixel_8
avdmanager create avd --name desktop_medium_api35 \
--package 'system-images;android-35;google_apis_playstore;x86_64' \
--device desktop_medium

# list available Andoid virtual devices
avdmanager list avd

# edit device settings
vim ~/.android/avd/desktop_medium_api35.avd/config.ini
  # PlayStore.enabled = yes

Start the Android device with emulator.

export ANDROID_SDK_ROOT=/path/to/sdk
export "PATH=${PATH}:${ANDROID_SDK_ROOT}/emulator"

# show help
emulator -help-all
emulator -help-environment # help on environment variables

# list all created AVDs
emulator -list-avds
  # desktop_medium_api35
  # pixel8_api35

# start the emulator (close its window to exit)
emulator -avd desktop_medium_api35

# 
emulator -avd desktop_medium_api35 -wipe-data

Rename a virtual device.

avdmanager move avd --name desktop_medium_api35 --rename desktop_medium_api35_old

Delete a virtual device.

avdmanager delete avd --name pixel8_api35
]]>Linda JanssonGitLab pipelines in monorepo2024-10-19T00:00:00+00:002024-10-19T00:00:00+00:00https://linda-jansson.com/gitlab-pipelines-in-monorepoGitLab pipelines in monorepo

In a monorepo as shown below, each sub-project folder contains its own pipeline file .gitlab-ci.yml. The top-level .gitlab-ci.yml conditionally includes a sub-folder .gitlab-ci.yml if that sub-folder’s files changed.

.
├── .gitlab-ci.yml
├── subproject1/
│   ├── .gitlab-ci.yml
│   ├── Dockerfile
│   └── src/
└── subproject2/
    ├── .gitlab-ci.yml
    ├── Dockerfile
    └── src/

The top-level .gitlab-ci.yml which uses include. See documentation for include at Use CI/CD configuration from other files.

# .gitlab-ci.yml
include:
  - local: subproject1/.gitlab-ci.yml
    rules:
      - changes:
          - subproject1/src/**/*
          - subproject1/Dockerfile

  - local: subproject2/.gitlab-ci.yml
    rules:
      - changes:
          - subproject2/src/**/*
          - subproject2/Dockerfile

# avoid empty pipeline errors when no includes are run
dummy:
  rules:
    - when: never
  script: ':'

The subproject pipelines below are written independently of each other. Their working directory is the repository root, so they use the files of their respective project folder.

# subproject1/.gitlab-ci.yml
subproject1:
  stage: build
  image: quay.io/buildah/stable:latest
  variables:
    PROJECT_DIR: subproject1
    STORAGE_DRIVER: vfs
    BUILDAH_FORMAT: oci
    IMAGE_NAME: ${CI_REGISTRY_IMAGE}/${CI_JOB_NAME_SLUG}:${CI_COMMIT_REF_SLUG}
  script:
    - |
      buildah login \
        --username "${CI_REGISTRY_USER}" \
        --password "${CI_REGISTRY_PASSWORD}" \
        "${CI_REGISTRY}"

      buildah build \
        -t ${IMAGE_NAME} \
        --label=CI_COMMIT_SHA=${CI_COMMIT_SHA} \
        -f ${PROJECT_DIR}/Dockerfile \
        ${PROJECT_DIR}/src

      buildah push ${IMAGE_NAME}

      if [ "${CI_COMMIT_BRANCH}" = "${CI_DEFAULT_BRANCH}" ]
      then
        buildah push "${IMAGE_NAME}" "${CI_REGISTRY_IMAGE}:latest"
      fi

# subproject2/.gitlab-ci.yml
subproject2:
  stage: build
  image: quay.io/buildah/stable:latest
  variables:
    PROJECT_DIR: subproject2
    STORAGE_DRIVER: vfs
    BUILDAH_FORMAT: oci
    IMAGE_NAME: ${CI_REGISTRY_IMAGE}/${CI_JOB_NAME_SLUG}:${CI_COMMIT_REF_SLUG}
  script:
    - |
      buildah login \
        --username "${CI_REGISTRY_USER}" \
        --password "${CI_REGISTRY_PASSWORD}" \
        "${CI_REGISTRY}"

      buildah build \
        -t ${IMAGE_NAME} \
        --label=CI_COMMIT_SHA=${CI_COMMIT_SHA} \
        -f ${PROJECT_DIR}/Dockerfile \
        ${PROJECT_DIR}/src

      buildah push ${IMAGE_NAME}

      if [ "${CI_COMMIT_BRANCH}" = "${CI_DEFAULT_BRANCH}" ]
      then
        buildah push "${IMAGE_NAME}" "${CI_REGISTRY_IMAGE}:latest"
      fi
]]>Linda JanssonRun podman containers as systemd services2024-10-19T00:00:00+00:002024-10-19T00:00:00+00:00https://linda-jansson.com/run-podman-containers-as-systemd-servicesRun podman containers as systemd services

The systemd unit files below are for starting a pod with containers as a non-root user.

# these have to be set for running systemctl with user scope
export XDG_RUNTIME_DIR=/run/user/$(id -u)
export XDG_CONFIG_HOME=${HOME}/.config

# directory to output podman logs
mkdir ~/logs

# install user systemd service files
mv *.service "${XDG_CONFIG_HOME}/systemd/user/"
systemctl --user daemon-reload

# start the pod along with pod containers
systemctl --user start pod.service

Pod service

The systemd unit file for the pod creates and removes the pod.

[Unit]
Description=Pod
Wants=network.target
After=network-online.target
RequiresMountsFor=
Requires=postgresql.service fluent-bit.service
Before=postgresql.service fluent-bit.service

[Service]
Type=forking
RemainAfterExit=yes
TimeoutStartSec=5m
PIDFile=%t/%n.pid
Restart=yes
RestartSec=30

ExecStartPre=/bin/rm --force %t/%n.pid %t/%n-pod-id
ExecStartPre=/usr/bin/podman pod create \
  --infra-conmon-pidfile %t/%n.pid \
  --pod-id-file %t/%n-pod-id \
  --name pod \
  --publish 2020:2020 \
  --publish 5432:5432 \
  --replace

ExecStart=/usr/bin/podman pod start --pod-id-file %t/%n-pod-id

ExecStop=/usr/bin/podman pod stop --ignore --pod-id-file %t/%n-pod-id --time 10

ExecStopPost=/usr/bin/podman pod rm --ignore --force --pod-id-file %t/%n-pod-id

[Install]
WantedBy=default.target

Fluent-bit service

mkdir "${XDG_CONFIG_HOME}/fluent-bit"
touch "${XDG_CONFIG_HOME}/fluent-bit/fluent-bit.conf"
touch "${XDG_CONFIG_HOME}/fluent-bit/parsers.custom.conf"

podman volume create fluent-bit-data

[Unit]
Description=Podman fluent-bit
Wants=network.target
After=network-online.target
RequiresMountsFor=%t/containers
BindsTo=pod.service
After=pod.service

[Service]
Type=notify
NotifyAccess=all
TimeoutStartSec=5m
TimeoutStopSec=70
Environment=PODMAN_SYSTEMD_UNIT=%n
Restart=yes
RestartSec=30
PIDFile=%t/%n.pid

ExecStartPre=/usr/bin/rm --force %t/%n.pid %t/%n-cid

ExecStart=/usr/bin/podman run \
  --cidfile %t/%n.cid \
  --cgroups=no-conmon \
  --rm \
  --sdnotify=conmon \
  --replace \
  --read-only \
  --pod pod \
  --volume fluent-bit-data:/var/data:U,Z,rw \
  --volume %h/logs:/var/log/containers:z,ro \
  --volume %E/fluent-bit/fluent-bit.conf:/fluent-bit/etc/fluent-bit.conf:z,ro \
  --volume %E/fluent-bit/parsers.custom.conf:/fluent-bit/etc/parser.custom.conf:z,ro \
  --name fluent-bit \
  docker.io/fluent/fluent-bit:3.1.9

ExecStop=/usr/bin/podman stop --ignore --cidfile %t/%n.cid --time 10

ExecStopPost=/usr/bin/podman rm --ignore --force --cidfile %t/%n.cid --time 10

[Install]
WantedBy=default.target

PostgreSQL service

mkdir "${XDG_CONFIG_HOME}/postgresql"
touch "${XDG_CONFIG_HOME}/postgresql/app-password"
touch "${XDG_CONFIG_HOME}/postgresql/postgresql-password"

podman volume create postgresql-data

[Unit]
Description=Podman postgresql
Wants=network.target
After=network-online.target
RequiresMountsFor=%t/containers
BindsTo=pod.service
After=pod.service

[Service]
Type=notify
NotifyAccess=all
TimeoutStartSec=5m
TimeoutStopSec=70
Environment=PODMAN_SYSTEMD_UNIT=%n
Restart=yes
RestartSec=30
PIDFile=%t/%n.pid

ExecStartPre=/usr/bin/rm --force %t/%n.pid %t/%n-cid

ExecStart=/usr/bin/podman run \
  --cidfile %t/%n.cid \
  --cgroups=no-conmon \
  --rm \
  --sdnotify=conmon \
  --replace \
  --read-only \
  --pod pod \
  --env POSTGRES_APP_DB=foi \
  --env POSTGRES_APP_USER=foi \
  --volume postgresql-data:/var/lib/postgresql/data:U,Z,rw \
  --volume "%E/postgresql/app-password:/run/secrets/app-password:z,ro" \
  --volume "%E/postgresql/postgres-password:/run/secrets/postgres-password:z,ro" \
  --log-driver=k8s-file \
  --log-opt path=%h/logs/postgresql.log \
  --log-opt max-size=1mb \
  --name postgresql \
  postgresql:latest

ExecStop=/usr/bin/podman stop --ignore --cidfile %t/%n.cid --time 10

ExecStopPost=/usr/bin/podman rm --ignore --force --cidfile %t/%n.cid --time 10

[Install]
WantedBy=default.target
]]>Linda JanssonVim cheatsheet2024-10-19T00:00:00+00:002024-10-19T00:00:00+00:00https://linda-jansson.com/vim-cheatsheetVim cheatsheet
Action command Description
:help [subject] Show help text on subject. E.g. :help options, :help ZQ, :help key-notation.
:show SETTING Show current value of setting.
:source ~/.vimrc Source vimrc file.
ZZ Save and quit (:wq).
ZQ Quit without saving (:q!).
gg / G / nG Go to first line / last line / line number n.
<C-d> / <C-u> Go down/up half a page.
<C-e> / <C-y> Scroll down/up without moving cursor (sticks to top/bottom).
zz / zt / zb Scroll to center the cursor.
ctrl+i / ctrl+o Go to next/previous jump position.
vip, vap Select paragraph about the cursor. vipip to select more.
<C-v>{I Insert before lines in block. Can be used to insert comment signs.
V Select lines.
gv Re-select last last selection.
'. 1v Go to last edit and re-select the same number of characters/lines.
. Repeat last action.
/term\c n N Search for term case-insensitive, go to next, go to previous. \C for case-sensitive.
/\%Vterm Search for term in selection. Must be in normal mode, not visual.
:g/regex Search for regex and list results.
:%s/PATTERN/REPLACEMENT/gc Search and replace all occurrences.
/term cgn ... Search and replace term (one by one). n to skip to next term.
:noh[lsearch] Stop highlighting search terms.
/<C-r>" Search for yanked text.
gJ Join line from with below.
:%!clang-format Run command clang-format on text.
:'<,'>!awk -f script.awk Run command awk on visual selection.
:read !date Insert output of command date.
:read FILE Insert contents of file FILE.
:new | 0read ! git diff # Open a file’s git diff in new window pane.
:Lexplore Open netrw in left pane.
<C-w>w Cycle pane focus.
<C-w>l Focus on left pane.
<C-w>| / <C-w>_ Maximize size of pane width/height.
<C-w>= Equalize sizes of all panes.
<C-w>10> / <C-w>-10> Increase/decrease pane width by 10 columns. 
# recover file from swapfile (see :help recovery / :help -r)
vim -r .swp

~/.vimrc

set exrc      " source .vimrc in project folders
set mouse=    " disable mouse
set list      " show listchars for tabs, trailing, nbsp
set listchars=tab:>>,trail:-,nbsp:+
set number relativenumber " hybrid line numbers (i.e. relative with current line as absolute)
set ignorecase smartcase  " search case-insensitive except when any character if uppercase

set tabstop=4 softtabstop=4 shiftwidth=4 expandtab smarttab
set autoindent         " indent new line as previous line
set formatoptions-=t   " don't auto-wrap text
set formatoptions-=c   " don't auto-wrap comments
set formatoptions-=r   " don't automatically insert comment leader on Enter
set fileencodings=utf-8,latin1 " default file encodings

let g:netrw_banner = 0         " disable banner
let g:netrw_liststyle = 3      " display as tree
let g:netrw_browse_split = 0   " reuse window when opening files
let g:netrw_winsize = 20       " explorer window size percentage

colorscheme slate

" Show file information in status line
set laststatus=2
set statusline=%f%=%y\ %{&fileformat}\ %{&fileencoding==\"\"?&encoding:&fileencoding}\ \ L%l:C%c\ 

set scrolloff=999 " screen lines kept above/below cursor (=999 to keep cursor in middle)

" use Space key as mapleader
nnoremap <space> <nop>
let mapleader=" "
set timeoutlen=2000 " 

nnoremap <leader>m :marks<CR>

" remap shift+tab to de-indent
inoremap <S-Tab> <C-O><<

" show matching parentheses with highlighted foreground, not background
hi MatchParen ctermfg=NONE ctermbg=NONE cterm=bold

" auto-save files under home
augroup AUTOSAVE
    autocmd!
    autocmd TextChanged,InsertLeave,FocusLost ~/* if &readonly == 0 && filereadable(bufname('%')) | silent update | endif
augroup END

" remove autosave if environment variable
if $VIM_AUTOSAVE=="no"
    au! AUTOSAVE
endif

Auto-complete parentheses

" auto-complete parentheses
inoremap {<space> {}<left>
inoremap (<space> ()<left>
inoremap [<space> []<left>
inoremap "<space> ""<left>
inoremap '<space> ''<left>
" except when completing manually
inoremap {} {}
inoremap () ()
inoremap [] []
inoremap "" ""
" auto-add closing bracket after enter
inoremap {<CR> {<CR>}<up><CR>

~/.vim/colors/custom.vim

set background=dark

" clear highlighting
hi clear
if exists("syntax_on")
    syntax reset
endif

"set t_Co=256
let g:colors_name = "simple"

"hi CTagsClass           -- no settings --
"hi CTagsGlobalConstant  -- no settings --
"hi CTagsGlobalVariable  -- no settings --
"hi CTagsImport          -- no settings --
"hi CTagsMember          -- no settings --
"hi DefinedName          -- no settings --
"hi EnumerationName      -- no settings --
"hi EnumerationValue     -- no settings --
"hi FoldColumn           -- no settings --
"hi Ignore               -- no settings --
"hi LocalVariable        -- no settings --
"hi ModeMsg              -- no settings --
"hi MoreMsg              -- no settings --
"hi Question             -- no settings --
"hi SpellBad             -- no settings --
"hi SpellCap             -- no settings --
"hi SpellLocal           -- no settings --
"hi SpellRare            -- no settings --
"hi StatusLine           -- no settings --
"hi StatusLineNC         -- no settings --
"hi Union                -- no settings --
"hi VisualNOS            -- no settings --
"hi WarningMsg           -- no settings --
"hi clear                -- no settings --

 
" http://vimdoc.sourceforge.net/htmldoc/syntax.html#:highlight
hi Normal                ctermfg=15    ctermbg=0     cterm=NONE       guifg=#000000 guibg=#ffffff gui=NONE

hi Boolean               ctermfg=8     ctermbg=NONE  cterm=NONE       guifg=#ff0000 guibg=NONE gui=NONE
hi Character             ctermfg=2     ctermbg=NONE  cterm=NONE       guifg=#2323ce guibg=NONE gui=NONE
hi Comment               ctermfg=7     ctermbg=NONE  cterm=NONE       guifg=#666666 guibg=NONE gui=NONE
hi Conditional           ctermfg=NONE  ctermbg=NONE  cterm=bold       guifg=NONE guibg=NONE gui=bold
hi Constant              ctermfg=2     ctermbg=NONE  cterm=NONE       guifg=#2323ce guibg=NONE gui=NONE
hi CursorColumn          ctermfg=NONE  ctermbg=NONE  cterm=underline  guifg=NONE guibg=NONE gui=NONE
hi CursorLine            ctermfg=NONE  ctermbg=NONE  cterm=NONE       guifg=NONE guibg=NONE gui=NONE
hi CursorLineNr          ctermfg=2     ctermbg=NONE  cterm=NONE       guifg=#2323ce guibg=NONE gui=NONE
hi ColorColumn           ctermfg=2     ctermbg=NONE  cterm=NONE       guifg=NONE guibg=#dddddd gui=NONE
hi Debug                 ctermfg=2     ctermbg=NONE  cterm=NONE       guifg=#2323ce guibg=NONE gui=NONE
hi Define                ctermfg=2     ctermbg=NONE  cterm=NONE       guifg=#2323ce guibg=NONE gui=NONE
hi Delimiter             ctermfg=8     ctermbg=NONE  cterm=NONE       guifg=#666666 guibg=NONE gui=NONE
hi DiffAdd               ctermfg=10    ctermbg=NONE  cterm=NONE       guifg=#00ff00 guibg=NONE gui=NONE
hi DiffChange            ctermfg=12    ctermbg=NONE  cterm=NONE       guifg=#0000ff guibg=NONE gui=NONE
hi DiffDelete            ctermfg=9     ctermbg=NONE  cterm=NONE       guifg=#ff0000 guibg=NONE gui=NONE
hi DiffText              ctermfg=NONE  ctermbg=NONE  cterm=NONE       guifg=NONE guibg=NONE gui=NONE
hi Directory             ctermfg=NONE  ctermbg=NONE  cterm=bold       guifg=NONE guibg=NONE gui=bold
hi Error                 ctermfg=1     ctermbg=NONE  cterm=NONE       guifg=#ff0000 guibg=NONE gui=NONE
hi ErrorMsg              ctermfg=1     ctermbg=NONE  cterm=NONE       guifg=#ff0000 guibg=NONE gui=NONE
hi Exception             ctermfg=NONE  ctermbg=NONE  cterm=bold       guifg=NONE guibg=NONE gui=italic
hi Float                 ctermfg=2     ctermbg=NONE  cterm=NONE       guifg=#2323ce guibg=NONE gui=NONE
hi Folded                ctermfg=NONE  ctermbg=8     cterm=bold       guifg=NONE guibg=#cccccc gui=NONE
hi Function              ctermfg=NONE  ctermbg=NONE  cterm=bold       guifg=NONE guibg=NONE gui=bold
hi HighlightedyankRegion ctermfg=NONE  ctermbg=NONE  cterm=bold       guifg=NONE guibg=NONE gui=italic
hi htmltagname           ctermfg=8     ctermbg=NONE  cterm=NONE       guifg=#666666 guibg=NONE gui=NONE
hi Identifier            ctermfg=NONE  ctermbg=NONE  cterm=bold       guifg=NONE guibg=NONE gui=bold
hi IncSearch             ctermfg=NONE  ctermbg=NONE  cterm=inverse,bold guifg=NONE guibg=NONE gui=inverse,italic
hi Include               ctermfg=NONE  ctermbg=NONE  cterm=bold       guifg=NONE guibg=NONE gui=bold
hi Keyword               ctermfg=NONE  ctermbg=NONE  cterm=bold       guifg=NONE guibg=NONE gui=bold
hi Label                 ctermfg=NONE  ctermbg=NONE  cterm=bold       guifg=NONE guibg=NONE gui=bold
hi LineNr                ctermfg=8     ctermbg=NONE  cterm=NONE       guifg=#666666 guibg=NONE gui=NONE
hi Macro                 ctermfg=2     ctermbg=NONE  cterm=NONE       guifg=#2323ce guibg=NONE gui=NONE
hi MatchParen            ctermfg=2     ctermbg=NONE  cterm=NONE       guifg=#2323ce guibg=NONE gui=bold
hi ModeMsg               ctermfg=8     ctermbg=NONE  cterm=NONE       guifg=#666666 guibg=NONE gui=NONE
hi NonText               ctermfg=8     ctermbg=NONE  cterm=NONE       guifg=#666666 guibg=NONE gui=NONE
hi Number                ctermfg=2     ctermbg=NONE  cterm=NONE       guifg=#2323ce guibg=NONE gui=NONE
hi Operator              ctermfg=8     ctermbg=NONE  cterm=NONE       guifg=#666666 guibg=NONE gui=NONE
hi PMenu                 ctermfg=NONE  ctermbg=NONE  cterm=NONE       guifg=NONE guibg=NONE gui=NONE
hi PMenuSbar             ctermfg=NONE  ctermbg=NONE  cterm=NONE       guifg=NONE guibg=NONE gui=NONE
hi PMenuSel              ctermfg=2     ctermbg=NONE  cterm=NONE       guifg=#2323ce guibg=NONE gui=NONE
hi PMenuThumb            ctermfg=NONE  ctermbg=NONE  cterm=NONE       guifg=NONE guibg=NONE gui=NONE
hi PreCondit             ctermfg=6     ctermbg=NONE  cterm=NONE       guifg=#16b723 guibg=NONE gui=NONE
hi PreProc               ctermfg=5     ctermbg=NONE  cterm=NONE       guifg=#333333 guibg=NONE gui=NONE
hi pythonescape          ctermfg=NONE  ctermbg=NONE  cterm=NONE       guifg=NONE guibg=NONE gui=NONE
hi Repeat                ctermfg=NONE  ctermbg=NONE  cterm=bold       guifg=NONE guibg=NONE gui=bold
hi Search                ctermfg=NONE  ctermbg=NONE  cterm=inverse    guifg=NONE guibg=NONE gui=inverse
hi SignColumn            ctermfg=NONE  ctermbg=NONE  cterm=inverse    guifg=NONE guibg=NONE gui=inverse
hi Special               ctermfg=2     ctermbg=NONE  cterm=bold       guifg=#2323ce guibg=NONE gui=bold
hi SpecialChar           ctermfg=2     ctermbg=NONE  cterm=bold       guifg=#2323ce guibg=NONE gui=bold
hi SpecialComment        ctermfg=2     ctermbg=NONE  cterm=bold       guifg=#2323ce guibg=NONE gui=bold
hi SpecialKey            ctermfg=8     ctermbg=NONE  cterm=bold       guifg=#666666 guibg=NONE gui=bold
hi Statement             ctermfg=NONE  ctermbg=NONE  cterm=NONE       guifg=NONE guibg=NONE gui=NONE
hi StatusLine            ctermfg=NONE  ctermbg=NONE  cterm=NONE       guifg=#666666 guibg=NONE gui=NONE
hi StatusLineNC          ctermfg=8     ctermbg=NONE  cterm=NONE       guifg=#333333 guibg=NONE gui=NONE
hi StorageClass          ctermfg=NONE  ctermbg=NONE  cterm=bold       guifg=NONE guibg=NONE gui=bold
hi String                ctermfg=2     ctermbg=NONE  cterm=NONE       guifg=#2323ce guibg=NONE gui=NONE
hi Structure             ctermfg=NONE  ctermbg=NONE  cterm=bold       guifg=NONE guibg=NONE gui=bold
hi TabLine               ctermfg=NONE  ctermbg=NONE  cterm=NONE       guifg=NONE guibg=NONE gui=NONE
hi TabLineFill           ctermfg=NONE  ctermbg=8     cterm=NONE       guifg=NONE guibg=#666666 gui=NONE
hi TabLineSel            ctermfg=NONE  ctermbg=NONE  cterm=bold       guifg=NONE guibg=NONE gui=bold
hi Tag                   ctermfg=NONE  ctermbg=NONE  cterm=NONE       guifg=NONE guibg=NONE gui=underline
hi Title                 ctermfg=NONE  ctermbg=NONE  cterm=bold       guifg=NONE guibg=NONE gui=NONE
hi Todo                  ctermfg=NONE  ctermbg=NONE  cterm=bold       guifg=NONE guibg=NONE gui=bold
hi Type                  ctermfg=NONE  ctermbg=NONE  cterm=bold       guifg=NONE guibg=NONE gui=bold
hi Typedef               ctermfg=NONE  ctermbg=NONE  cterm=bold       guifg=NONE guibg=NONE gui=bold
hi Underlined            ctermfg=NONE  ctermbg=NONE  cterm=underline  guifg=NONE guibg=NONE gui=underline
hi VertSplit             ctermfg=NONE  ctermbg=NONE  cterm=NONE       guifg=#333333 guibg=NONE gui=NONE
hi Visual                ctermfg=NONE  ctermbg=NONE  cterm=inverse    guifg=NONE guibg=NONE gui=inverse
hi WildMenu              ctermfg=2     ctermbg=NONE  cterm=NONE       guifg=#2323ce guibg=NONE gui=NONE

Check current value with e.g. :highlight Comment.

Re-orders lines

dd          Delete (and yank) the lines in the order they should be in
:display    Display registers
"1P         Paste from register 1 above current line
.           Repeat the paste action while updating register 1 to the next register
]]>Linda JanssonUnicode encoding2024-09-08T00:00:00+00:002024-09-08T00:00:00+00:00https://linda-jansson.com/unicode-encodingUnicode encoding

The Unicode standard encodes characters as 21-bit codepoint values. The codepoints are stored in one of the formats: UTF-32, UTF-16, or UTF-8.

  • UTF-32 stores the 21-bit unicode data in a 32-bit integer with 11 bits of zero-padding.
  • UTF-16 stores unicode data in either a single 16-bit integer or within two 16-bit integers (called a surrogate pair). The high 16-bit word and the low 16-bit word each has 10 bits for the unicode data – which is only 20 bits and not the full 21 bits. The other bits are used to recognize the encoding.
  • UTF-8 stores 21-bit values within one, two, three, or four 8-bit integers. For multibyte sequences the initial bits of the first byte identify the sequence length. Subsequent bytes start with 10 followed by 6 bits for unicode data.

The diagram belows shows how Unicode codepoint values are encoded in bits for the different encoding formats. x is part of the codepoint bit number and the literal numbers are what identifies the Unicode encoding.

          Codepoint range:       Bit encoding:
UTF-32:   0x0 - 0x1F FFFF        0000 0000 000x xxxx xxxx xxxx xxxx xxxx

UTF-16:   0x0000 - 0xD7FF        xxxx xxxx xxxx xxxx
          0xD800 - 0xDFFF        (not valid codepoints)
          0xE000 - 0xFFFF        xxxx xxxx xxxx xxxx
          0x010000 - 0x10FFFF    1101 10xx xxxx xxxx, 1101 11xx xxxx xxxx

UTF-8:    0x0 - 0x7F             0xxx xxxx
          0x80 - 0x7FF           110x xxxx, 10xx xxxx
          0x800 - 0xFFFF         1110 xxxx, 10xx xxxx, 10xx xxxx
          0x10000 - 0x1FFFFF     1111 0xxx, 10xx xxxx, 10xx xxxx, 10xx xxxx

MUTF-8

Codepoints should be encoded into the minimum length byte sequences for UTF-16 and UTF-8, but it’s possible to encode them with more bytes than necessary by simply setting the codepoint value bits to zeroes for the higher bytes.

For example, 0 can be encoded with two byte sequences (11 data bits) instead of one as: 1100 0000 1000 0000 (0xC080). The Modified UTF-8 encoding (MUTF-8) uses this “overlong encoding” for the NULL value to avoid it being encoded (and possibly treated) as the end-of-string (i.e. \0).

Byte-order-mark (BOM)

A byte-order-mark (BOM) in the beginning of the character stream marks the byte endianness of the sequence. This is relevant for UTF-16 and UTF-32 to recognize if the first byte of the encoded sequence is in the high byte or in the low byte of the integer – as the endianness of the system must match the sequence to load the bytes into 16/32-bit integers correctly.

For UTF-8 there is no need for a BOM, since each byte is loaded into a separate integer. However, there is an optional (and discouraged) BOM for UTF-8 that can be used to identify the encoding as UTF-8.

The Unicode codepoint for the BOM is U+FEFF, which is the “zero width non-breaking space” character.

            First bytes    Check
UTF-32LE    FF FE 00 00    uint32_t bom == 0xFFFE0000
UTF-32BE    00 00 FE FF    uint32_t bom == 0x0000FEFF
UTF-16LE    FF FE .. ..    uint16_t bom == 0xFFFE
UTF-16BE    FE FF .. ..    uint16_t bom == 0xFEFF
UTF-8       EF BB BF ..    1110 [1111], 10[11 1011], 10[11 1111] = 0xFEFF

Most CPU systems are little endian.

]]>Linda Jansson