lenciel

Often referred to as the "swiss army of knife" for TCP/IP networking, [Netcat][1] is an extremely versatile Linux utility that allows you to do anything under the sun using TCP/UDP sockets. It is one of the most favorite tools for system admins when they need to do networking related troubleshooting and experimentation.

In this tutorial, I am sharing a few useful netcat examples, although the sky is the limit when it comes to possible netcat use cases. If you are using netcat regularly, feel free to share your use case.

Note that when you are binding to well-known ports (0-1023) with nc, you need root privilege. Otherwise, run nc as a normal user.

1. Test if a particular TCP port of a remote host is open.

$ nc -vn 192.168.233.208 5000

lenciel

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE plist PUBLIC "-//Apple//DTD PLIST 1.0//EN" "http://www.apple.com/DTDs/PropertyList-1.0.dtd">
<plist version="1.0">
<dict>
  <key>KeepAlive</key>
  <true/>
  <key>Label</key>
  <string>autossh.lenciel</string>
  <key>ProgramArguments</key>
  <array>

lenciel

Latency Comparison Numbers

Note: "Forked" from Latency Numbers Every Programmer Should Know

Event	Nanoseconds	Microseconds	Milliseconds	Comparison
L1 cache reference	0.5	-	-	-
Branch mispredict	5.0	-	-	-
L2 cache reference	7.0	-	-	14x L1 cache
Mutex lock/unlock	25.0	-	-	-

lenciel

;Notes:
;  - Shell expansion ("~" or "$HOME") is not supported.  Environment
;    variables can be expanded using this syntax: "%(ENV_HOME)s".
;  - Comments must have a leading space: "a=b ;comment" not "a=b;comment".
; 
; Put this file in /etc/supervisord.conf

[unix_http_server]
file=/tmp/supervisor.sock   ; (the path to the socket file)

lenciel

By installing Vim with ruby support from the sources, it is build against the system wide installation of ruby. If you already installed Vim and/or ruby with sudo apt-get install vim (or sudo apt-get install ruby) or with brew install vim (e.g. brew install ruby) if you are using OS X, remove it completely from your system to install the latest version of Vim.

Install rbenv

I'm installing rbenv on different machines so I created the following script (named rbenv_install.sh) to install ruby 1.9.2-p320:

cd $HOME
sudo rm -rf .rbenv
git clone git://github.com/sstephenson/rbenv.git .rbenv
echo 'export PATH="$HOME/.rbenv/bin:$PATH"' >> ~/.bash_profile

lenciel

基础知识

• 计算机软硬件基础
• 计算机网络
• 操作系统
• 数据结构和算法
• 设计模式
• 以及其他各种你应该懂的东西

前端开发

• 前端标准/规范

lenciel

Keybase proof

I hereby claim:

• I am lenciel on github.
• I am lenciel (https://keybase.io/lenciel) on keybase.
• I have a public key ASAdpEB6qCAu--QM2AurwajcSOdLJ0NCda7NCK9RYsX6iAo

To claim this, I am signing this object:

lenciel

%vertical-align {
  position: relative;
  top: 50%;
  -webkit-transform: translateY(-50%);
  -ms-transform: translateY(-50%);
  transform: translateY(-50%);
}

.element p {
  @extend %vertical-align;

lenciel

一般 Android 用户都知道同时按下音量减和电源键的屏幕截图方式，不过作为开发者，可能需要一个更为简便的方式将屏幕截图保存至开发电脑上。

该方式仅需在终端执行一条命令即可，涉及调用系统内置的 screencap 工具：

```
adb shell screencap -p | sed 's/\r$//' > screen.png
```

screencap 本身支持标准输出，所以可以用管道符链接。但是 adb shell 会将结果中的 LF 转换为 CR+LF（为了兼容性考虑？），于是会将 png 的格式破坏。于是这里使用行编辑器 sed 将 LF 前的 CR 移除。

lenciel

#!/bin/sh
 
# Shell script to install your public key on a remote machine
# Takes the remote machine name as an argument.
# Obviously, the remote machine must accept password authentication,
# or one of the other keys in your ssh-agent, for this to work.
#
# http://www.devthought.com/2009/09/19/get-ssh-copy-id-in-mac-os-x/
#