Knowledge worth sharing

To create same environment in python, you must know requirements.txt, it includes packages dependencies and let you install by a single command, a requirements.txt looks like this :

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beautifulsoup4==4.6.0
certifi==2018.1.18
chardet==3.0.4

To generate requirements.txt

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# Without using virtual environment
pip install pipreqs
pipreqs /path/to/project

# With virtual environment
pip freeze > requirements.txt

Install packages from requirements.txt :

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pip install -r requirements.txt

pip install bypass SSL certificate :

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pip install --trusted-host pypi.python.org <package_name>

# Combine with requirements.txt
pip install --trusted-host pypi.python.org -r requirements.txt

Reference

https://github.com/bndr/pipreqs
pip install --help is your friend.

Directly copy db from ip :

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mongo <ip>
use admin
db.runCommand({copydb:1, fromdb:"<DB Name>", todb:"<DB Name>", fromhost:"<DB HOST IP>"})

Export / Restore DB

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# Export
mongodump --db <dbname>

# Restore
mongorestore --port <port number> <path to backup folder>
# e.g. mongorestore --port 27017 X:\dump

Note :

1. Run commands in administrator mode
2. If commands not found, excute commands under mongodb bin folder, windows default path : C:\Program Files\MongoDB\Server\3.2\bin\

Reference :

https://docs.mongodb.com/manual/tutorial/backup-and-restore-tools/

To convert Markdown into Word format, pandoc is the best tool I found.

• Step1 : Install pandoc
• Step2 : pandoc myfile.md -o myfile.docx

• ctrl + alt + / : Show Keyboard Shortcut
• ctrl + 口|| : Screenshot
• ctrl + shift + 口|| : Screenshot region
• ctrl + shift + i : Open developer tools
• alt + search : Toggle Caps Lock
• alt + shift + m : Open file manager
• ctrl + space : Change input method
• shift + esc : Open task manager
• ctrl + alt + t : Open terminal
• search + button between esc and power : F1~F10

Recently I found that AWS Cloud9 is so good that help me coding in my chromebook.
Here I want to share how I use it with my nodejs project, it is free, fast and easy.

1. Go to https://aws.amazon.com/tw/cloud9/
2. Click Create environment and choose your preference
3. Wait seconds to see your cloud9 IDE
4. To switch keyboard setting, go to Edit > Keyboard mode > Sublime Vim Emac

5. Setup nodejs developement environment via terminal

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   # Clone repo git clone repo # Switch node version nvm install --lts # Use new version nvm use stable # Install yarn sudo npm install -g yarn # Install package yarn # Start application npm start

6. To browse application webpage, go to Preview > Preview Running Application

Always use man commandName to know what the command is before copy and paste.

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# Open a new shell with root, exit with "exit" or "ctrl+d"
sudo su -

# Show how to use a command
man command

# Find first excutable path
whichis command

# Find every excutable path
whereis command

# Use proxy
export http_proxy=http://server-ip:port/
export https_proxy=http://server-ip:port/

# Check CentOS version
rpm --query centos-release

# Read file
cat filename

# Write file (after excute, type content and ctrl+d to save)
cat > filename

# RPM install
rpm -ivh file.rpm

# switch to last directory
cd -

# Download file with wget -c=continue download
wget -c --header "Cookie: foo=bar" http://url/to/file`

# Force reboot immediately
reboot -f

# Rename files
rename <old name> <new name> <Regex match>

# Connect to openvpn
sudo openvpn --config client.ovpn

# List port listening
lsof -i :<port>

# kill process by id
kill PID

# List recent command history
history

# excute command from history
!<search text>
!vi # excute recent command contains vi

Recently my co-worker recommends a great VS extension NPM task runner. Instead of running NPM task via a separate terminal, it will discover NPM task via package.json and run them inside Visual Studio by a double-click.

Install via Tools > Extensions and Updates > Online > Search NPM task runner

Task Runner Explorer locate in View > Other Windows > Task Runner Explorer
Run task by double-click tasks in sidebar, close it by x button

If your task fails, it probably references to wrong NPM or Node.js, to fix it change the order in Tools > Options > Projects and Solutions > External Web Tools. I lift-up ${PATH} to the second one.

For security reason, private CI server may not have internet access. Instead, it connect to private registry like ProGet. To install public npm package, ProGet connector is here to help, steps as following :

1. Go to Connectors => create connectors => Feed type:npm => Save
2. Go to feeds => Create New Feed => Feed type:npm => Feed name:npm
3. Feed Connectors => add connector => registry.npmjs.org
4. Set up npm via command line in server
   npm config set registry http://{progethost}/npm/npm

Now try npm install, it should work as it connect to public npm registry.

Reference : http://inedo.com/support/documentation/proget/feed-types/npm

一時興起參加了 LeetCode 的 Weekly Contest #40，用Javascript只解出了第一題計算二元樹每層平均值，思維是用兩個陣列，一個存每層的平均，一個存每層的總數量，最後相除得到每層的平均，實作如下：

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/**
 * Definition for a binary tree node.
 * function TreeNode(val) {
 *     this.val = val;
 *     this.left = this.right = null;
 * }
 */
/**
 * @param {TreeNode} root
 * @return {number[]}
 */

var averageOfLevels = function(root) {
    var sumArr = [];
    var countArr = [];
    var sum = function(node, level) {
        if (!node) return
        if (!sumArr[level]) sumArr[level] = 0;
        sumArr[level] += node.val;
        if (!countArr[level]) countArr[level] = 0;
        countArr[level]++;
        sum(node.left, level + 1);
        sum(node.right, level + 1);
    }

    sum(root, 0);
    var meanArr = sumArr.map((sum, level) => sum / levelCountArr[level]);
    return meanArr;
};

Sometimes I want to create empty branch for gh-pages or server-packages instead of branch from master, I will excute following command:

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git checkout --orphan empty.branch.name
git rm --cached -r .
echo "init empty branch" > README.md
git add README.md
git commit -m "init empty branch"

Stackoverflow reference