/GC

Dump of dev stuff

GC

Navigation: BASH | GIT | SSH | PHP | SQL | NODE | JS | TS | jQuery | VUE | MacOSX | Links

WTF?

Goodness Corp? or Garbage Collector? Who knows...

Maybe its Gists Collection, no its Gone Cuties! LOL! ROFL! and LMAO...

I started this collection named "GC" in relationship but not only for JS.

You would feel as on a dump waste as well as happiest of happy-nanny nyan cat!

To be clear, this is not just a garbage-like log, but mix of proven solutions even with copy-paste from good sites.

Enjoy!

HTML Colors Table

MARKDOWN

HTML/CSS

<style>
@import '/main.css';
</style>
<!-- or -->
<link rel="stylesheet" href="/main.css">
  • Minimal pic
<img src="data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAAEAAAABCAYAAAAfFcSJAAAADUlEQVR42mP8z8BQDwAEhQGAhKmMIQAAAABJRU5ErkJggg==">

<img src="data:image/gif;base64,R0lGODlhAQABAPABAP///wAAACH5BAEKAAAALAAAAAABAAEAAAICRAEAOw==">

background-image:url(data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAAEAAAABCAYAAAAfFcSJAAAADUlEQVR42mP8z8BQDwAEhQGAhKmMIQAAAABJRU5ErkJggg==);

background-image:url(data:image/gif;base64,R0lGODlhAQABAIAAAP///wAAACH5BAEAAAAALAAAAAABAAEAAAICRAEAOw==);
  • Fixed-width breakpoints media queries:
@media (min-width: 576px) {
  .container {
    max-width: 540px;
  }
}

@media (min-width: 768px) {
  .container {
    max-width: 720px;
  }
}

@media (min-width: 992px) {
  .container {
    max-width: 960px;
  }
}

@media (min-width: 1200px) {
  .container {
    max-width: 1140px;
  }
}

Hex values from 100% to 0% alpha:

100% — FF, 99% — FC, 98% — FA, 97% — F7, 96% — F5, 95% — F2, 94% — F0, 93% — ED, 92% — EB, 91% — E8
90% — E6, 89% — E3, 88% — E0, 87% — DE, 86% — DB, 85% — D9, 84% — D6, 83% — D4, 82% — D1, 81% — CF
80% — CC, 79% — C9, 78% — C7, 77% — C4, 76% — C2, 75% — BF, 74% — BD, 73% — BA, 72% — B8, 71% — B5
70% — B3, 69% — B0, 68% — AD, 67% — AB, 66% — A8, 65% — A6, 64% — A3, 63% — A1, 62% — 9E, 61% — 9C
60% — 99, 59% — 96, 58% — 94, 57% — 91, 56% — 8F, 55% — 8C, 54% — 8A, 53% — 87, 52% — 85, 51% — 82
50% — 80, 49% — 7D, 48% — 7A, 47% — 78, 46% — 75 ,45% — 73, 44% — 70, 43% — 6E, 42% — 6B, 41% — 69
40% — 66, 39% — 63, 38% — 61, 37% — 5E, 36% — 5C, 35% — 59, 34% — 57, 33% — 54, 32% — 52, 31% — 4F
30% — 4D, 29% — 4A, 28% — 47, 27% — 45, 26% — 42, 25% — 40 ,24% — 3D, 23% — 3B, 22% — 38, 21% — 36
20% — 33, 19% — 30, 18% — 2E, 17% — 2B, 16% — 29, 15% — 26, 14% — 24, 13% — 21, 12% — 1F, 11% — 1C
10% — 1A, 9% — 17, 8% — 14, 7% — 12, 6% — 0F, 5% — 0D, 4% — 0A, 3% — 08, 2% — 05, 1% — 03, 0% — 00

https://fonts.google.com/specimen/FONTNAME
https://fonts.adobe.com/fonts/FONTNAME

JS

So, why Javascript?

I really not have an answer immediately...

Because, for example I can just run, in one line:

"foo".length

Or another one

"foo".match(/FOo/i)

Or even

++"foo1".match(/FOo(\d+)/i)[1]

Or IIFE, JIT, events bubbling, functions binding, whatever... you know?

Nevermind, if you do ;) Its kick your ASs! Just remember - GC!

Ok, well, shuffling some another stuff...

    function arraysIntersect (a, b) {
      try {
        for (let i = a.length; i--;) {
          for (let j = b.length; j--;) {
            if (a[i] === b[j]) return true
          }
        }
        return false
      } catch (e) {
        return null
      }
    }
  • Random float number between min and max
    function rndA(min, max) {
      return Math.random() * (max - min) + min
    }
  • Random integer number between min and max
    function rndB (min, max) {
      return Math.floor(Math.random() * (max - min + 1)) + min
    }
  • Random point in unit circle
    function rndC() {
      let t = 2 * Math.PI * Math.random()
      let u = Math.random() + Math.random()
      let r = (u>1) ? 2 - u : u
      return [r * Math.cos(t), r * Math.sin(t)]
    }
  • Capitalize string
    function capitalize(s) {
      return s.charAt(0).toUpperCase() + s.slice(1);
    }

  • Normalize string, removing duplicated spaces (or any repeating 'format character')

    str.replace(/ +/g, ' ') or str.replace(/\s\s+/g, ' ')

  • Date in SQL format

    new Date().toISOString().substr(0, 10)

    Datetime: new Date().toISOString().substr(0, 19).replace('T', ' ')

  • Unix timestamp for moment: Date.now()

  • Shift existing Date object by n milliseconds

    d.setTime(d.getTime() + 1000)) // set 1 second shift

  • void operator

    void (1+2) // undefined

// arrow function not to return value
void setInterval(() => { ... }, 1500)

// escape context from polluting
void function aRecursion(i) {
  if(i > 0) {
    console.log(i--)
    aRecursion(i)
  }
}(3)
console.log(typeof aRecursion) // undefined

  • Destructuring

    [a, b] = [10, 20]

[a, b, ...rest] = [10, 20, 30, 40, 50] // rest is [30, 40, 50]

({a, b} = {a: 10, b: 20}) // `a` , `b` now in context

var o = {p: 42, q: true}
var {p: foo, q: bar} = o // vars `foo` is 42, `q` is true in context

let key = 'z'
let {[key]: foo} = {z: 'bar'}  // `foo` is 'bar' in context

let userFields = {
   ...(email && {email}),
   ...(name && {name}),
}

  • JSX conditional attributes

    <Link
  href="some"
  {...(foo === 'bar' && {className: styles.active})}
>Text</Link>

  • Variables as object keys

    let kProp = 'foo'
let obj = {
  name: 'Bob',
  [kProp]: 'Bar',
...
}
obj.foo

  • Advanced object key-prop loop

    var obj = {x:200, y:100, ...}
Object.entries(obj).forEach(v => {
  // v[0] : x, y, ...
  // v[1] : 200, 100, ...
})

  • Function default arguments

    function foo(v, p = true) {
  console.log(v, p);
}
foo(1); // 1, true

  • Default function argument value, when implementation above not supported by js engine

    function test(v) {
  var v = (typeof v === 'undefined') ? 'Foo' : v
  console.log(v)
}
test() // Foo
test(1) // 1

  • Object pure clone, shallow copy, new object in memory

    /* make object's shallow copy
 * src - source object
 return new object */ 
function clone(src) {
  let out, v, k;
  if (typeof src !== 'object' || src === null) {
    return src;
  }
  out = Array.isArray(src) ? [] : {}
  for (k in src) {
    v = src[k];
    out[k] = clone(v);
  }
  return out;
}

  • Object pure clone, filtered by keys

    /* make object's shallow copy, using key filter mask (only on root level)
 * src - source object
 * keys - array of keys to be filtered, strings
 * includes - boolean flag means include or exclude operation, true by default
 return new object
 depends on clone() function */
function cloneFk(src, keys, includes = true) {
  let out, v, k;
  if (typeof src !== 'object' || src === null) {
    return src;
  }
  out = Array.isArray(src) ? [] : {}
  for (k in src) {
    if (Array.isArray(keys) && !includes && keys.includes(k)) continue;
    if (Array.isArray(keys) && includes && !keys.includes(k)) continue;
    v = src[k];
    out[k] = clone(v);
  }
  return out;
}

  • Prototype extending

var world = {
  width: 2048,
  heigh: 2048,
  spawnX: 420,
  spawnY: 420
}
function Entity(o) {
  console.log('*[Entity]', o)
  var _ = o || {}
  this.x = _.x || 0
  this.y = _.y || 0
}
Entity.prototype.draw = function(t) {
  console.log('*[Entity.draw]', this.x, this.y, t)
}
function Player (o) {
  console.log('*[Player]', o)
  Entity.call(this, o)
  this.x = world.spawnX
  this.y = world.spawnY
  this.width = 42
  this.height = 42
}
Player.prototype = Object.create(Entity.prototype)
Player.prototype.constructor = Player
Player.prototype.draw = function(t) {
  console.log('*[Player.draw]', this.x, this.y, this.width, this.height, t)
}
function Sky() {
  console.log('*[Sky]', arguments)
  Entity.apply(this, arguments)
}
Sky.prototype = Object.create(Entity.prototype, {
  foo: {
    writable: true,
    configurable: true,
    value: 'Bazz'
  },
  draw: {
    writable: false,
    configurable: false,
    value: function(t) {
        console.log('*[Sky.draw]', this.x, this.y, t)
    }
  },
})
Sky.prototype.constructor = Sky
var sky = new Sky()
var player = new Player()
var target = new Entity({ x: 1000, y: 1000 })
sky.draw()
target.draw()
player.draw()

  • Async IIFE

    // async block
(async (data) => {
  // let b = await a(...)
  // return b
})

({foo:'Bar'}) // input

// output
.then(v => {
  // result
})
.catch(e => {
  // error
})

  • Sleep for milliseconds implementation

    function sleep(ms) {
   return new Promise(resolve => setTimeout(resolve, ms))
}

  • Parse form-urlencoded string to Object

    function url_decode(s) {
    return s
        .split('&')
        .map(s => s.split('='))
        .map(pair => pair.map(decodeURIComponent))
        .reduce(function(memo, [key, value]) {
            if (!(key in memo)) { memo[key] = value }
            else {
                if (!(memo[key] instanceof Array))
                    memo[key] = [memo[key], value]
                else
                    memo[key].push(value)
            }
            return memo
        }, {})
}

  • generate UUID, browser

    modern browsers already have crypto.randomUUID()

    function uuidv4() {
    return 'xxxxxxxx-xxxx-4xxx-yxxx-xxxxxxxxxxxx'.replace(
/[xy]/g,
function(c) {
        var r = Math.random() * 16 | 0,
        v = c == 'x' ? r : (r & 0x3 | 0x8);
        return v.toString(16);
    })
}

  • generate UUID, node

    function uuidv4() {
    return ([1e7]+-1e3+-4e3+-8e3+-1e11).replace(
/[018]/g,
c => (c ^ crypto.getRandomValues(new Uint8Array(1))[0] & 15 >> c / 4).toString(16)
    )
}

  • Ajax call, fetch polyfill

    var token = '...'
var form = new FormData(document.getElementById('login-form'));
fetch('/login', {
  method: 'POST',
  headers: {
    'Content-Type': 'application/x-www-form-urlencoded', // application/json
    'Authorization': 'Bearer ' + token
  },
  mode: 'cors',
  cache: 'no-cache',
  credentials: 'include',
  body: form
})
.then(function(res) {
  return res.json();
})
.then(function(data) {
  console.log('*[response]', data);
})
.catch(function(err) {
  console.error(err)
});

  • Js module (ES5)

    var app = (function (initData) {
//private
  var data = {
    foo1: '1',
  }
  Object.assign(data, initData)
  var init = function(newData) { Object.assign(data, newData) }
  var test = function() { console.log(data) }
//public
return {
  init: init,
  test: test
}
})({
 foo: 'Bar',
})
console.log(app)
app.init({foo2: 'Bar2'})
app.test()

  • Load JS

    let el = document.createElement('script')
el.setAttribute('src', url)
document.head.appendChild(el)

  • Load CSS

    let el = document.createElement('link')
el.type = 'text/css'
el.rel = 'stylesheet'
el.href = url
document.getElementsByTagName('head')[0].appendChild(el)

  • Trigger DOM Event

var event = new MouseEvent('click');
var target = document.getElementById('target'); 
target.dispatchEvent(event);

  • Wait for Element promise

    function waitForElement(selector, timeout) {
  return new Promise(function(resolve, reject) {
    var ts = Date.now();
    function queryEl() {
      var el = document.querySelector(selector);
      if (el) return resolve(el);
      if (Date.now() - ts > timeout) {
        return reject(new Error('Element ' + selector + ' not found'));
      }
      setTimeout(queryEl, 1000);
    }
    queryEl();
  });
}

// Usage example: awaiting 30 seconds for element with class="test"
waitForElement('.test', 30000)
  .then(function(el) {
    // TEST PASSED
    console.error('Found element .test:', el.innerText);
  })
  .catch(function(err) {
    // element not found and time is out
    console.error(err.message);
  });

  • Fix npm install errors like next:

npm ERR! code EINVALIDTAGNAME
npm ERR! Invalid tag name ">=^16.0.0" of package "react@>=^16.0.0": Tags may not have any characters that encodeURIComponent encodes.
  • Run npm install --legacy-peer-deps

TS

JQuery

  • Entrypoint
$(document).ready(function() {
  //job
})
  • Bind event handler to element with attribute <a href="#action" id="mybutton"></a>
$('#mybutton').on('click', function(e) {
  e.preventDefault()
  //job
})
  • Trigger DOM event
$('selector').trigger('click')
  • Trigger focus event and do extra stuff
$('selector').focus(function() {
  $(this).next('span').css('display', 'inline').fadeOut(1000)
});
  • AJAX request
$.ajax({
  url: '/api/endpoint',
  type: 'POST',
  data: { foo: 'Bar' },
  cache : false,
  processData: false,
  contentType: false,
  headers: {
    'X-CSRF-Token': $('meta[name="csrf-token"]').attr('content')
    // customize request headers
  },
  error: function(xhr) {
    var errors = xhr.responseJSON.errors || {}
    //handle errors
  },
  beforeSend: function(xhr) {
    //show loader indicator
  },
  success: function(data) {
    console.log('*[XHR SUCCESS], data)
    //OK
  }
})

// add custom function
(function( $ ) {

    $.fn.superFeature = function() {
        // super feature code
    };

}( jQuery ));
// use us
$().superFeature();

PIXIJS

NODE.JS

apt-get install gcc g++ make curl build-essential
curl -sL https://deb.nodesource.com/setup_16.x | sudo -E bash -
sudo apt-get install -y nodejs

  • List global modules: npm -g list

  • Install module globally: npm i -g live-stream-radio

  • Vue Developer Must Have: npm i -g @vue/cli-service-global @vue/cli npm-check-updates serve nmv pm2 nodemon

  • Install and add to package.json dependencies: npm i -P <package>

  • Install and add to package.json devDependencies: npm i -D <package>

  • Uninstall: npm uninstall <package>

  • Full re-install npm-managed project: rm -rf ./node_modules && rm ./package-lock.json && npm i --force

  • Find all available npm module versions: npm view node-sass versions or npm show node-sass@* version

  • Update npm itself: sudo npm update -g

  • List updatable: npm outdated -g

  • Find installed foo: npm list -g | grep foo

  • Fix broken npm: npm cache clean --force

  • Useful npms:

dotenv dotenv-expand pm2 nodemon serve http-server eslint express body-parser socket.io knex cron redis mongodb mongoose nodemailer multer bcrypt web3 passport passport-jwt puppeteer jimp node-ipc list.js node-webcam mediasoup johnny-five handlebars, >130 handlebars helpers

  • Tingodb - embedded db version with storage in filesystem and API close to Mongodb, tingodb api

  • socket.io socket.io-server socket.io-client

  • upgrade package.json dependencies to latest versions

    npm i -g npm-check-updates
ncu -u
npm install

  • async block in main context

    (async () => {
  await foo();
  // rest of code
})();

  • argc/argv example: const doClean = process.argv.length > 2 && process.argv.indexOf('--clean') !== -1

  • Reading a .py config file into json-valid string

    Python file config.py:

    #!/usr/bin/env python
config = {
	"foo": "Bar",
...
}

    Nodejs code to read python file:

    var pycfg = require('fs').readFileSync('../config.py').toString()
pycfg = pycfg.replace(/#.*\n|\r/g, '').replace('config = ', '').replace(/'/g, '"')
var cfg = JSON.parse(pycfg)
console.log(cfg.foo)

  • Nodejs console input

    const readline = require('readline')
const rl = readline.createInterface({
  input: process.stdin,
  output: process.stdout
})
rl.question('Whatsup?', (answer) => {
  console.log(`input: ${answer}`)
  rl.close()
})

  • Nodejs list network interfaces

    // long
const hostname = os.hostname();
const { networkInterfaces } = os;
const nets = networkInterfaces();
const interfaces = {}
for (const name of Object.keys(nets)) {
  for (const net of nets[name]) {
      // Skip over non-IPv4 and internal (i.e. 127.0.0.1) addresses
      // 'IPv4' is in Node <= 17, from 18 it's a number 4 or 6
      const familyV4Value = typeof net.family === 'string' ? 'IPv4' : 4
      if (net.family === familyV4Value && !net.internal) {
          if (!interfaces[name]) {
              interfaces[name] = [];
          }
          interfaces[name].push(net.address);
      }
  }
}
// { en0: [ '192.168.1.72' ] }
console.log('*interfaces', interfaces);
// short, but with callback
const os = require('os');
const dns = require('dns');
dns.lookup(os.hostname(), function (err, addr, fam) {
  console.log('*ADDR:', addr);
});

  • node-weak

  • btoa() polyfill for Nodejs, encode to Base64 (Binary to Ascii)

    Buffer.from(asciiData).toString('base64')

  • atob() polyfill for Nodejs, decode from Base64 (Ascii to Binary)

    Buffer.from(b64Encoded, 'base64').toString()

  • fetch() polyfill for Nodejs: import fetch from 'isomorphic-unfetch' (should be installed via npm i isomorphic-unfetch)

  • Convert commonJS node app to ESmodule, not modifying type to "module" in package.json and not refactoring all existing exports

    • do not change type of module in package.json

    • rename entrypoint file from JS to MJS (e.g. app.js to app.mjs)

    • now you can use new export style like import { Foo } from 'bar' and export { Foo }

    • add require() function polyfill to save all existing require's imports:

    import { createRequire } from 'module';
const require = createRequire(import.meta.url);
    • __dirname global polyfill:
    const url = require('node:url');
const __filename = url.fileURLToPath(import.meta.url);
const __dirname = path.dirname(__filename);

VUE

component.vue

<template>
  <foo-bar v-model="x" @click.prevent.stop="barFoo" />
  <!-- in VUE3 multiple root nodes supported -->
  <img src="@/assets/logo.png" />
  <form @submit.prevent><select v-model="ch" ref="selCh">...</select></form>
</template>
<script>
/* eslint-disable no-console,vue/no-unused-components */
import { mapState } from 'vuex'
import FooBar from 'theme/components/Foo'
export default {
  name: 'Bar',
  components: {
    FooBar
  },
  props: {
    msg: {
      type: String,
      required: false,
      default: ''
    }
  },
  data () {
    return {
      x: 0
    }
  },
  created () {},
  beforeMount () {},
  computed: {
    ...mapState({
      currentUser: state => state.user.current,
      barX () {
        return 1000 * this.x
      }
    })
  },
  methods: {
    barFoo() {}
  }
}
</script>
<style type="css">
@import '~@/assets/css/main.css';
</style>

Vue3 Guide

Pass elements by refs composed by v-for

Properly vuex state mutation

Set up Vue 3 linting in VSCode

Eslint Vuejs rules

Init VUE PWA boilerplate

sudo npm i -g @vue/cli @vue/cli-service-global
vue init projectname
...a bunch of options
cd projectname
npm run serve

Vue cli web GUI: vue ui

Instant vue prototyping

  • Create vue component

    mkdir test
cd test
touch Test.vue

  • Edit Test.vue (vim Test.vue)

  • Optional dependencies

    Install optional dependencies via terminal: npm init -y && npm i dependency

    Import them in vue js code:

    import { foo } from 'dependency'

  • Run via vue-cli instantly: vue serve Test.vue

  • Open http://localhost:8080

  • Define port and automatically open browser: vue serve -o -p 5000 Test.vue

  • Optionally existing index.html will be reused

Nuxt.js

BASH

SHELL

  • Create Symbolic Link: ln -s source target

  • Pack dir to TAR + GZ: tar -zcvf name.tgz path

  • Unpack TGZ: tar -xzf name.tgz

  • Unpack gzipped file: gunzip -k db.sql.gz

  • Pack dir to BZ2 without absolute path: tar -c -j -f site1.tbz -C /var/www site1

  • Pack 1 file (.gz added automatically): gzip path

  • Copy from your pc to host over ssh: scp source user@host:pathTo

  • Copy from host to your pc over ssh: scp user@host:pathFrom pathTo

For example: scp -P 2222 root@IP-ADDR:/root/.bash_profile ./bash_profile.txt

  • Download: wget URL

  • Advanced download: curl -fsSL URL -O (or replace -O to -o path)

  • Restart service in debian/ubuntu: systemctl restart nginx

  • Stats

    top, htop - system load

    free -m, vmstat -s, cat /proc/meminfo - memory

    ps -ax | grep foo - find process by name

    systemctl show - services

    df -h (du) - disk space

    ip link show - list network interfaces

    ifconfig, iwconfig, arp -a, ping google.com - network

    netstat -lntp, netstat -Ana|grep LISTEN|grep 80 - find process bind to port

  • Show listening ports: sudo netstat -tunlp

  • Create user: sudo useradd -m username

  • Set user password: sudo passwd username

  • Add user to root group: sudo usermod -a -G sudo username

  • Add user FOO to group BAR: sudo usermod -a -G BAR FOO

  • Recursively set owner:group: chown -R username:group /path/*

  • Recursively fix read/write permissions:

    chmod 755 $(find /path/to -type d)
chmod 644 $(find /path/to -type f)

  • Grant read/write permissions required by the web application:

    cd /var/www/website
find . -type d -exec chmod 755 {} \;
find . -type f -exec chmod 644 {} \;
chown -R www-data:www-data .

  • Remove user: sudo killall -u username && sudo deluser --remove-home -f username

  • Show Debian/Ubuntu linux version: lsb_release -a

  • List media drives: fdisk -l

  • List usb devices: lsusb

  • Backup disk to file, than restore it

    dd if=/dev/hda1 of=./part1.image - to backup
dd if=./part1.image of=/dev/hda1 - to restore

  • Write usb bootable from iso file:

    dd if=./image.iso of=/dev/sdx ( should be sda or sdb or sdc )

  • Get random seed: openssl rand 64 | base64 or

    node -e "console.log(require('crypto').randomBytes(64).toString('base64'))"

  • xargs

  • xclip

  • Install common dev stuff (like ssh, vim and mc) missing after clean install on debian-like os:

    sudo -s
apt-get update
apt-get upgrade -y
apt install -y linux-headers-$(uname -r) net-tools wireless-tools apt-transport-https ca-certificates \
dkms build-essential software-properties-common python gcc g++ make curl bzip2 git subversion \
openssl libssl-dev openssh-client openssh-server screen vim mc
    • special only for ubuntu:

    ubuntu-restricted-extras

    • minimal MTA (sendmail)

    nullmailer mailutils

  • Reconfigure package, running postinstall script again: sudo dpkg-reconfigure nullmailer

  • Web developer env:

sudo snap install --classic certbot
sudo ln -s /snap/bin/certbot /usr/bin/certbot
apt install -y nginx curl nodejs npm php php-cli php-fpm php-json php-common php-mysql php-zip php-gd php-mbstring php-curl php-xml php-pear php-bcmath
curl -sS https://getcomposer.org/installer -o composer-setup.php
sudo php composer-setup.php --install-dir=/usr/local/bin --filename=composer

Edit /etc/php/7.4/fpm/php.ini, set correct path's (like upload_tmp_dir) and other critical PHP settings

  • configure network adapter

    -- eth1 - interface name

    -- sudo vi /etc/network/interfaces :

    auto eth1
	iface eth1 inet dhcp

    (ESC, i, type..., ESC, :wq)

    -- sudo systemctl restart networking

  • Update snap packages when it whan't:

sudo killall snap-store
sudo snap refresh snap-store

  • screen - terminal multiplexor - keeps your terminal session on server

    • apt install screen

    • screen - start new session

    • screen -ls - list running sessions

    • screen -r - reconnect

    • CTRL + A, D - disconnect

    • CTRL + A, C - open new terminal tab

    • CTRL + A, 0..9 - switch tab directly

    • CTRL + A, capital K than press y - to kill session

    • cool adjustment with display tabs, cpu, time - place this file on home dir .screenrc

vbell off
altscreen on
defutf8 on
termcapinfo xterm ti@:te@
hardstatus alwayslastline
hardstatus string '%{= w}%-w[ %{= W}%n %t%{-} ]%+w%=[ %{= W}%H%{-} ] [ %{= W}%l%{-} ] [ %{= W}%d.%m.%Y %c:%s%{-} ]'
  • Network scan
sudo apt-get install nmap -y
nmap -sP 192.168.1.0/24

  • locale: Cannot set LC_* errors

    locale: Cannot set LC_CTYPE to default locale: No such file or directory
locale: Cannot set LC_ALL to default locale: No such file or directory
...

    • Client-side fix:

      • Set appropriate env vars (EXPORT LC_ALL=$LANG)

      • Disable sending locale information over terminal (on OSX unset Set locale environment variables on startup in Advanced settings tab)

    • Server-side fix:

       apt-get purge locales
   apt install locales (locales-all)
   dpkg-reconfigure locales
   locale -a

  • Current date in SQL fotmat: cdate +'%F %T'

  • Erase and watch Laravel log file

#!/bin/bash
DT=`date +'%F'`
truncate -s 0 ./storage/logs/laravel-$DT.log
tail -f ./storage/logs/laravel-$DT.log

  • Import environment variables from .env file

    unamestr=$(uname)
if [ "$unamestr" = 'Linux' ]; then
    export $(grep -v '^#' .env | xargs -d '\n')
elif [[ "$unamestr" = 'FreeBSD' || "$unamestr" = 'Darwin' ]]; then
    export $(grep -v '^#' .env | xargs -0)
fi

  • Install Certbot

  • Generate new certificates on working system with nginx

    certbot --nginx -d example.com -d www.example.com

  • Generate SSL certificates for domains via Certbot

    certbot certonly --standalone -d example.com -d www.example.com

  • Update expired sertificates

    certbot renew

  • Generate SSL certificate for localhost

  • CI in 1 line of code ;)

    crontab -e - to open cron jobs file editor

    */1 * * * * cd /home/user/project && /usr/bin/git pull -q origin master >/dev/null 2>&1

    The periodical job to pull from master branch

    YOU SHOULD USE WEBHOOKS / GITLAB CI INSTEAD!

  • fix issues with video driver

add-apt-repository ppa:graphics-drivers/ppa
apt-get update
ubuntu-drivers autoinstall
  • Upload via CURL
curl -i -X POST -H "Content-Type: multipart/form-data" 
-F "data=@test.mp3;userid=1234" http://mysuperserver/media/upload/

curl \
  -F "userid=1" \
  -F "filecomment=This is an image file" \
  -F "image=@/home/user1/Desktop/test.jpg" \
  http://URL
  • CURL Ajax POST request with Authorization header:
#!/bin/bash

token=${@: -1}
if [ -z "${token}" ]; then
echo Enter token:
read token
fi

curl -H 'content-type: application/json' \
-H "Authorization: Bearer $token" \
-v -X POST -d '{"foo": "Bar", "baz": 0.842}' http://127.0.0.1:3000/api/fun

APT

dpkg --get-selections | grep foo - find all packages by name foo

dpkg-query --status foo - info about package foo

apt-get remove foo - delete package foo

apt-get autoremove - delete all obsolete packages

apt-get install -y gcc g++ make nodejs npm - install list of packages in one line without confirmation

CRON

crontab -l - show current cron jobs

crontab -e - open crontab file with default editor

Crontab file example:

# m h dom mon dow user	    command
# every minute
  * * *   *   *   www-data  wget -O - -q -t 1 http://localhost/api/cron

or

# run CMD every hour
0 * * * * CMD

Run every 10 minutes: */10 * * * *

SSH

ssh-keygen -t rsa -b 4096 -C "username@example.com"

  • Prevent git@gitlab.com: Permission denied (publickey). connection error

    eval "$(ssh-agent -s)"
ssh-add -l
ssh-add -K ~/.ssh/id_rsa (or other file)

or just ssh add

  • How to add new ssh key

  • test access rights: ssh -vT git@github.com

  • view ssh key fingerprint: ssh-keygen -lf ~/.ssh/id_rsa.pub

  • Ssh agent

  • To easy add existing key (not .pub file) from this pc to host - ssh-copy-id -i ~/.ssh/mykey user@host

  • To test key - ssh -i ~/.ssh/mykey user@host

  • Cannot connect to remote host with error:

    @@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@
@    WARNING: REMOTE HOST IDENTIFICATION HAS CHANGED!     @
@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@
IT IS POSSIBLE THAT SOMEONE IS DOING SOMETHING NASTY!
Someone could be eavesdropping on you right now (man-in-the-middle attack)!
It is also possible that a host key has just been changed.

    edit .ssh/known_hosts deleting old cached host fingerprint, than it will be recreated at next attemp

    or fix with terminal cmd: ssh-keygen -R *ip_address_or_hostname*

  • Tunneling

    ssh -N -L localhost:6379:localhost:6379 example.com (-L ... -L ... to multiply number of ports)

  • autossh, Permanent ssh tunnel

  • Mount fs via sftp

    apt install sshfs
mkdir /media/server1
sshfs -o allow_other,follow_symlinks,IdentityFile=~/.ssh/keyfile username@hostname:/ /media/server1
...
umount /media/server1

  • Restricted access to host's sshd

    sudo vim /etc/ssh/sshd_config
add line: AllowUsers goodiman good2
sudo systemctl restart sshd

  • Pass user password to ssh cmd (last resort, if you cannot ssh -i key...)

    sudo apt install sshpass
sshpass -p "password" ssh user@host

GIT

  • Pretty printed commits history

git log --pretty=oneline --abbrev-commit

  • Config
git config --global --get user.name
git config --global --get user.email

git config --global --list
git config --global user.name "John Doe"
git config --global user.email john@example.com

git config --get user.name
git config --get user.email

git config user.name "Your project specific name"
git config user.email "your@project-specific-email.com"
  • Disable Fast-forward strategy
git config merge.ff false
git config --get merge.ff

  • Global git settings: ~/.gitconfig

  • The local (project) configuration will be in your repository's .git/config

git init

git remote -v
git remote add

git branch

git checkout -b new_branch
git checkout other_branch
git checkout master

git branch -d localBranchName
git push origin --delete remoteBranchName

git status
git pull

git merge

git add .
git commit -m "msg"

git push -u origin master

git rm -r ObsoleteDir

git log --oneline

git checkout -- .
git reset --soft HEAD^
git reset --hard HEAD^
git reset HEAD <file>
git revert HASHCODE
git stash
git stash list
git checkout BRANCH_WHERE_YOU_STASHED
git stash apply
git stash drop

git tag -d TAGNAME
git push origin :refs/tags/TAGNAME
  • Convert existing non-empty directory into a Git working directory and push files to a remote repository
cd <localdir>
git init
git add .
git commit -m 'message'
git remote add origin <url>
git push -u origin master

YARN

sudo npm i -g yarn or brew install yarn to install Yarn

yarn - bring yarn into existing npm project

yarn install foo - install foo package

yarn remove foo - uninstall foo package

yarn dev - run dev npm script

  • fix apt-get update error The following signatures were invalid: EXPKEYSIG 23E7166788B63E1E Yarn Packaging <yarn@dan.cx>:

    curl -sS https://dl.yarnpkg.com/debian/pubkey.gpg | sudo apt-key add -

OSX

  • Install Homebrew

    /bin/bash -c "$(curl -fsSL https://raw.githubusercontent.com/Homebrew/install/HEAD/install.sh)"

  • Monitor highest consuming processes

    top -o cpu

    top -o rsize

  • Background services

    launchctl list (with | grep whatever)

    brew services list

    instead of list use NAME start|stop|restart to control

  • Shebang for /usr/local/bin/* shell scripts

    #!/bin/sh

    Don't forget to set executable permissions - use chmod +x /.../bin/foo to set it

  • Screenshots

    CMD + SHIFT + 3 - whole screen

    CMD + SHIFT + 4 - rectangle selection dialog

    Find recently made screenshots

  • Degree symbol ° - OPTION(ALT) + SHIFT + 8

  • Process on port

    sudo lsof -PiTCP -sTCP:LISTEN

    sudo lsof -nPi :6379

  • Mount via sftp/sshfs

    • Install osxfuse and sshfs for mac:

      brew cask install osxfuse
brew install sshfs

    • linux install: sudo apt-get install sshfs

    • Test ssh connection:

      ssh -i ~/.ssh/keyfile username@hostname

    • Mount remote share:

      mkdir /mountpath
sshfs username@hostname:/ /mountpath

    • Unmount

      umount /mountpath or diskutil umount force /mountpath

  • Remote SSH to Mac

    • Open the Apple menu in the upper left corner of the screen, and select "System Preferences...".

    • Under "Internet & Wireless", select "Sharing".

    • In the left column of services, enable "Remote Login".

    • Highlight the "Remote Login" service and enable access for the users you would like to have SSH access.

    • You can select all users, or specific users by selecting "Only these users:" and adding the appropriate users by clicking "+".

    • Take note of the command displayed underneath the words "Remote Login: On" in the upper middle part of the screen.

    • Write this command down as you will need it to log in from a different system.

    • If your firewall is enabled (which it is by default), you may need to restart the firewall to allow SSH communications to pass through port 22.

    • Open "System Prefrences", click "Security", and restart the Firewall.

    • Test that the firewall is not blocking SSH access by going to a different system and entering the ssh login command in step 6 above.

    • If you cannot login, restart the firewall or reboot.

  • How to create a bootable installer for macOS

    • Install proper installation app from Appstore (Install macOS X*)

    • sudo /Applications/Install\ macOS\ Mojave.app/Contents/Resources/createinstallmedia --volume /Volumes/VOLUMENAME

  • Change the default web browser or email app on your Mac

  • TextEdit as ASCII editor

  • Supporting Associated Domains

  • Fix for CLI error

    xcodebuild[3125:22662] Requested but did not find extension point with identifier Xcode.IDEKit.ExtensionSentinelHostApplications for extension Xcode.DebuggerFoundation.AppExtensionHosts.watchOS of plug-in com.apple.dt.IDEWatchSupportCore
xcodebuild[3125:22662] Requested but did not find extension point with identifier Xcode.IDEKit.ExtensionPointIdentifierToBundleIdentifier for extension Xcode.DebuggerFoundation.AppExtensionToBundleIdentifierMap.watchOS of plug-in com.apple.dt.IDEWatchSupportCore

    when running git (xcodebuild) commands

Virtualbox

  • Install Guest Additions on guest Debian/Ubuntu:

    • Required packages: dkms linux-headers-$(uname -r) build-essential

    • Add virtual cdrom via Devices > Insert Guest Additions CD image

    • Mount virtual cd sudo mount /dev/cdrom /media/cdrom

    • Run sudo sh /media/cdrom/VBoxLinuxAdditions.run

    • Reboot

  • Mount shared directory inside guest Debian/Ubuntu (Guest Additions required):

    • add shared dir in Virtual machine configuration, with specifying work dir share name

    • inside guest os create mount point dir mkdir ~/work

    • mount sudo mount -t vboxsf work ~/work

ESLINT

/* eslint-disable no-undef */
...
/* eslint-enable no-undef */

.eslintrc.js, rules:

// no debug
"no-console": process.env.NODE_ENV === "production" ? "warn" : "off",
"no-debugger": process.env.NODE_ENV === "production" ? "warn" : "off",
// singlequotes
"quotes": ["error", "single", { "avoidEscape": true }],
// no semicolons
"semi": ["error", "never"],
// no non-ascii chars in variables
"id-match": ["error", "^[a-zA-Z0-9_$]*$", { "properties": true, "onlyDeclarations": false }]

PYTHON

  • Python REPL

  • Awesome Python

  • Check os for python support: python --version, python3 --version, pip -V

  • Linux installation: sudo apt install python3 python3-pip

  • OSX installation: brew install python3

  • Install PIP manager:

    • curl https://bootstrap.pypa.io/get-pip.py -o get-pip.py
    • python3 get-pip.py

PHP

0_O Wooot!?

if (!empty($_SERVER['HTTP_CLIENT_IP'])) {
  $ip = $_SERVER['HTTP_CLIENT_IP'];
} elseif (!empty($_SERVER['HTTP_X_FORWARDED_FOR'])) {
  $ip = $_SERVER['HTTP_X_FORWARDED_FOR'];
} else {
  $ip = $_SERVER['REMOTE_ADDR'];
}

  • Set correct timezone for script: date_default_timezone_set('Europe/Kiev');

  • SQL date: php -r 'echo date('Y-m-d').PHP_EOL;'

  • next day SQL date: date('Y-m-d', strtotime('+1 day'))

  • Timestamps:

$beginOfDay = strtotime('today', $timestamp);
$endOfDay = strtotime('tomorrow', $beginOfDay) - 1;
$endOf2Weeks = strtotime('today', strtotime('+2 weeks'));
  • is number don't have float point
if (!function_exists('is_decimal')) {
    function is_decimal($n)
    {
        return is_numeric($n) && floor($n) != $n;
    }
}
  • Parse .json file
$json = file_get_contents("./data.json");
if ($json) {
    try {
      $data = json_decode($json, true);
    } catch(Exception $e) {
      // handle parse error
      // $e->getMessage()
    }
} else {
  // error, no input data
}
  • File upload
$uploaddir = './public/';
$tmpdir = './tmp/';
$fileKey = 'file1';
$fileSizeLimit = 2097152; // 2MB
$allowedFileTypes = ['image/png', 'image/jpeg', 'image/jpg', 'image/gif'];
$file = $_FILES[$fileKey] ?? null;
if ($file && $file['tmp_name']) {
  $fileName = basename($file['name']);
  $fileSize = $file['size'];
  $fileType = $file['type'];
  if ($fileName && $fileSize < $fileSizeLimit && in_array($fileType, $allowedFileTypes)) {
    $fileTmpPath = $tmpdir . ;
    if (is_uploaded_file($file['tmp_name'])) {
      $fp = explode('.', $fileName);
      $fileExtension = strtolower(array_pop($fp));
      $uploadFileName = join('.', $fp) . '.' . $fileExtension;
      $uploadPath = $uploaddir . $uploadFileName;
      if (move_uploaded_file($file['tmp_name'], $uploadPath)) {
        // Upload success
      }
    }
  }
}

  • Simple Auth (2 files)

    1. cms.php (login + password required to enter)
    <?php
session_start();
if (empty($_SESSION['user'])) {
  header("Location: login.php");
  exit;
}
if (!empty($_GET['logout'])){
 unset($_SESSION['user']);
 session_destroy();
 header("Location: login.php");
}
?>
<div>
<h1>Restricted resource<h1>
<a href="?logout=true">Logout</a>
</div>
    1. login.php (login form + authenticator)
    <?php
session_start();
$users = [
  'admin' => 'a029d0df84eb5549c641e04a9ef389e5'
];
$login = $_POST['login'] ?? null;
$password = $_POST['password'] ?? null;
if (
  $login !== null && $login !== ''
  && $password !== null && $password !== ''
  && array_key_exists($login, $users) && $users[$login] === md5($password)
) {
  $_SESSION['users'] = [
    'login' => $login,
    'password' => $password
  ];
  header("Location: cms.php");
  exit;
} 
?>
<form method="post">
<div>Username: <input type="text" name="login"></div>
<div>Password: <input type="password" name="password"></div>
<input type="submit" name="submit" value="Login">
</form>

  • Guzzle HTTP request CurlFactory exception cURL error 60: SSL certificate problem: unable to get local issuer certificate fix

    [openssl]
openssl.cafile=c:\webserver\php\extras\ssl\cacert.pem

  • Strings

    php -r "echo PHP_EOL;" > eol

Have we equal output of file to String.fromCharCode(13,10) or just '\n' ?

what about this \x0A \x0D , x13 x10 ?

Blame it on the typewriters - better yet, that lever or button on the right side of them. The one used to start typing on the next line. When you activate it, it causes

the carriage to 'return' to the right so the hammers are lined up on the left side of the paper (carriage return)
the carriage to roll up so the hammers are lined up on the next 'line' down (line feed)

In the early 1900's teletypwriters were used to relay messages. Teletypwriters were descendants of the telegraph, and used a code similar to ASCII, called Baudot (or Murray) code. An operator could type into the teletypewriter (tty for short) and print a message on another tty far away.

In this Baudot code, two special characters were designated for a Carriage Return(0x02) and a Line Feed(0x08). Baudot code went the way of the dinosaur for reasons outside the scope of this discussion, but the CR and LF characters were adopted by ASCII with different values:

CR = 0x0D = \015 = \r
LF = 0x0A = \012 = \n

historically

Macintosh: \r
Windows  : \r\n
Unix     : \n

different operating systems interpret a logical newline

Unix     : \n = \012
Macintosh: \n = \015
Windows  : \n = \012     if handled as ASCII
Windows  : \n = \015\012 if handled as binary

But why x13 x10 ?

0x0D is hexadecimal 0D which is decimal 13 which is octal 15 (or 015). Similarly, 0x0A is hexadecimal 0A which is decimal 10 which is octal 12 (or 012).

Following php docs about strings interpolation:

Double quoted

If the string is enclosed in double-quotes ("), PHP will interpret more escape sequences for special characters:

\n - linefeed (LF or 0x0A (10) in ASCII) \r - carriage return (CR or 0x0D (13) in ASCII) \t - horizontal tab (HT or 0x09 (9) in ASCII) \v - vertical tab (VT or 0x0B (11) in ASCII) \e - escape (ESC or 0x1B (27) in ASCII) \f - form feed (FF or 0x0C (12) in ASCII) \ - backslash $ - dollar sign " - double-quote [0-7]{1,3} - the sequence of characters matching the regular expression is a character in octal notation \x[0-9A-Fa-f]{1,2} the sequence of characters matching the regular expression is a character in hexadecimal notation

As in single quoted strings, escaping any other character will result in the backslash being printed too. Before PHP 5.1.1, the backslash in \{$var} had not been printed. The most important feature of double-quoted strings is the fact that variable names will be expanded. See string parsing for details.

NGINX

server {
  listen 80;
  server_name domain;
  root /var/www/domain/public;
  disable_symlinks off;
  set $path_info "";
  location / {
    index index.php index.html;
    try_files $uri $uri/ /index.php?$query_string /index.html;
    location = /favicon.ico {
      log_not_found off;
    }
    location = /robots.txt {
      log_not_found off;
    }
    location ~ /\. {
      return 404;
    }
  }
  location ~ ^/(login|logout|profile|register)/ {
    index index.html;
  }
  location ~ /\.ht {
    deny all;
  }
  location /static/ {
    alias /var/www/domain/static/;
  }
  location ~ \.php$ {
    include snippets/fastcgi-php.conf;
    fastcgi_pass unix:/run/php/php7.4-fpm.sock;
    #fastcgi_pass 127.0.0.1:9000;
    #fastcgi_pass docker-servicename:9999;
  }
  location ~ ^/(login|logout|profile|register|reset|reset-confirm) {
    rewrite /(.*) /$1 break;
    proxy_redirect off;
    proxy_set_header Host $host;
    proxy_set_header X-Real-IP $remote_addr;
    proxy_set_header X-Forwarded-For $proxy_add_x_forwarded_for;
    proxy_set_header X-Forwarded-Proto $scheme;
    proxy_set_header Host $http_host;
    proxy_pass http://api:${API_PORT};
  }
  location /api {
    rewrite /(.*) /$1 break;
    proxy_redirect off;
    proxy_http_version 1.1;
    proxy_set_header Upgrade $http_upgrade;
    proxy_set_header Connection "upgrade";
    proxy_set_header Host $host;
    proxy_set_header X-Real-IP $remote_addr;
    proxy_set_header X-Forwarded-For $proxy_add_x_forwarded_for;
    proxy_set_header X-Forwarded-Proto $scheme;
    proxy_set_header Host $http_host;
    proxy_pass http://api:3001;
    proxy_buffering off;
  }
}

DB

SQL

  • Install: sudo apt-get install -y mysql-server
  • Init root user: sudo mysql_secure_installation
  • Set root(user) credentials:
  • sudo mysql
  • ALTER USER 'root'@'localhost' IDENTIFIED WITH mysql_native_password BY 'your_new_password';
  • FLUSH PRIVILEGES;

select from_unixtime(2147483647)

=>

2038-01-19 05:14:07 - 32-bit time_t limit (2038-year timestamp overflow)

  • Date/time conversion functions:

    SELECT FROM_UNIXTIME(UNIX_TIMESTAMP(STR_TO_DATE('Oct 19 2018 10:00PM', '%M %d %Y %h:%i%p')),'%m-%d-%Y %h:%i:%p'); => 10-19-2018 10:00:PM

  • Select with grouping for 'daily count'

select
 year(created_at) date_year,
 month(created_at) date_month,
 day(created_at) date_day,
 count(*) as users_count
from users
where
 # todo: set variable date range here
 year(created_at) = 2020 and month(created_at) = 12
group by
 year(created_at), month(created_at), day(created_at)
  • Add user with credentials (myuser mypassword) and set all privilegies to mydb
CREATE USER 'myuser'@'%' IDENTIFIED BY 'mypassword';
GRANT ALL PRIVILEGES ON mydb.* TO 'myuser'@'%';
  • Add privilegies for user on db
GRANT ALL PRIVILEGES ON *.* TO 'myuser'@'%';
FLUSH PRIVILEGES;
  • Rename database olddb newdb
CREATE DATABASE newdb DEFAULT CHARSET utf8;

RENAME TABLE olddb.table1 TO newdb.table1;
RENAME TABLE olddb.table2 TO newdb.table2;
...

DROP DATABASE olddb;
  • Execute dynamic statement (truncate a table only if it exists)
SET @tableName := 'your_table_name';
SET @schemaName := 'your_schema_name';
IF EXISTS (
    SELECT 1
    FROM information_schema.tables
    WHERE table_schema = @schemaName
    AND table_name = @tableName
) THEN
    SET @truncateStmt := CONCAT('TRUNCATE TABLE ', @schemaName, '.', @tableName);
    PREPARE truncateStmt FROM @truncateStmt;
    EXECUTE truncateStmt;
    DEALLOCATE PREPARE truncateStmt;
END IF;

  • reset MySQL root password (ubuntu)

  • Install vim inside mysql docker container: microdnf install -y vim (then you can vim /etc/my.cnf)

  • Increase system var value that affects default limit 1024 of GROUP_CONCAT()

    • Show system var: select @@GLOBAL.group_concat_max_len;

    • In mysqld config (/etc/my.cnf):

      [mysqld]
group_concat_max_len = 10000

Mongo DB

mongoose.connect(MONGO_URI, options, (err) => { ... })

Where:

  • const MONGO_URI = mongodb+srv://<username>:<password>@<cluster_name>.<host>/<database>

  • const options = {useNewUrlParser: true, useUnifiedTopology: true}

  • (err) => { ... } callback, if no err object in first argument - connection success

Mongo CLI - authorize as db admin

mongo
use admin
db.auth('admin', passwordPrompt())

Mongo CLI - create normal user with credentials and full access to DB_NAME

  • Authorize as admin

  • use DB_NAME
db.createUser({user:'USERNAME', pwd:'PASW', roles:[{role:'readWrite', db:'DB_NAME'}]})

Mongodb on OSX

Start/stop server: brew services start|stop mongodb-community

Add root user

  • Edit config: vim /usr/local/etc/mongod.conf

  • Add section that turns off authorization

    security:
  authorization: disabled

  • Restart service brew services restart mongodb-community

  • Login to cli and add paticular user

    mongo
use admin
db.createUser({user:"admin",pwd:"password",roles:[{role:"root",db:"admin"}]});
exit

  • Comment out with # or delete authorization: disabled from mongod.conf

  • Restart service brew services restart mongodb-community

Redis

redis-cli

VI(M)

  • Press ESC to switch mode

    dd - delete line

    :w - save, :q - quit

    :wq - write and quit

    :q! - quit without saving

  • Cut and paste

    Position the cursor where you want to begin cutting.

    Press v to select characters (or uppercase V to select whole lines).

    Move the cursor to the end of what you want to cut.

    Press d to cut (or y to copy).

    Move to where you would like to paste.

    Press P to paste before the cursor, or p to paste after.

    Copy and paste is performed with the same steps except for step 4 where you would press y instead of d:

    d = delete = cut

    y = yank = copy

Deleted or copied text is placed in the unnamed register. If wanted, a register can be specified so the text is also copied to the named register. A register is a location in Vim's memory identified with a single letter. A double quote character is used to specify that the next letter typed is the name of a register.

For example, you could select the text hello then type "ay to copy "hello" to the a register. Then you could select the text world and type "by to copy "world" to the b register. After moving the cursor to another location, the text could be pasted: type "ap to paste "hello" or "bp to paste "world". These commands paste the text after the cursor. Alternatively, type "aP or "bP to paste before the cursor.

You remember? ", than register, than operation (yY dD pP)

And yes... Please don’t cut the purple trees!

Change the lineendings in the view:

:e ++ff=dos
:e ++ff=mac
:e ++ff=unix

This can also be used as saving operation (:w alone will not save using the lineendings you see on screen):

:w ++ff=dos
:w ++ff=mac
:w ++ff=unix

And you can use it from the command-line:

for file in $(ls *cpp)
do 
  vi +':w ++ff=unix' +':q' ${file}
done

DOCKER

WINDOWS

ANDROID

MISC

  • Get first line of string

    js: s.split('\n')[0]

    php: strtok($s, "\n")

    py: s.split('\n', 1)[0] or another py: s.splitlines()[0]

  • cyrillic characters

ы Ы э Э ё Ё ъ Ъ і І ї Ї є Є ґ Ґ №

  • Capture webcam

  • Set permission for video device: usermod -a -G video USERNAME

  • Install v41-utils: sudo apt-get install -y v4l-utils

  • Check available devices: sudo v4l2-ctl --list-devices

  • Get info about device: sudo v4l2-ctl --device=/dev/video0 --all

  • Install ffmpeg: sudo apt-get install -y ffmpeg

  • Run capture: ffmpeg -f oss -f video4linux2 -s 640x480 -t 24 -i /dev/video0 ./www/video0.mpg

DECENTRALIZATION

  • bitcoin
sudo add-apt-repository ppa:bitcoin/bitcoin
sudo apt update
sudo apt install bitcoin-qt bitcoind
bitcoin-qt

LINKS