how to install mysql2 gem on windows

There is a useful link in here stackoverflow.

Rails reads excel by using spreadsheet

thanks to stackoverflow.com I found this fruitful example and I share it

# load the gem
require 'spreadsheet'

# In this example the model MyFile has_attached_file :attachment
@workbook = Spreadsheet.open(MyFile.first.attachment.to_file)

# Get the first worksheet in the Excel file
@worksheet = @workbook.worksheet(0)

# It can be a little tricky looping through the rows since the variable
# @worksheet.rows often seem to be empty, but this will work:
0.upto @worksheet.last_row_index do |index|
  # .row(index) will return the row which is a subclass of Array
  row = @worksheet.row(index)

  @contact = Contact.new
  #row[0] is the first cell in the current row, row[1] is the second cell, etc...
  @contact.first_name = row[0]
  @contact.last_name = row[1]

  @contact.save
end

While saving simple_form data, rails save values as NULL problem

Problem solution is here.

The model you have are heavily populated with attr_accessor. attr_accessor is a way to create "virtual attributes" in Ruby / Rails, as it defines a custom getter and setter method, which will essentially define the "attributes" for use on the system

The problem you have is attr_accessor, in the simplest of terms, will not permit your data to be saved in the database. This will be one of the bigger issues you have - you need to get rid of any attr_accessors which override your database attributes.

It should be removed the attr_accessor methods from your model

How to capture packets

While I surf the internet, I came across a web site(www.opensourceforu.com) about how to capture packets physical layer to application layer. I like this explanation:

Capturing packets means collecting data being transmitted on the network. Every time a network card receives an Ethernet frame, it checks if its destination MAC address matches its own. If it does, it generates an interrupt request. The routine that handles this interrupt is the network card’s driver; it copies the data from the card buffer to kernel space, then checks the ethertype field of the Ethernet header to determine the type of the packet, and passes it to the appropriate handler in the protocol stack. The data is passed up the layers until it reaches the user-space application, which consumes it.

Google Chrome using with proxy in Linux

If you also reach internet via proxy, you can encounter this problem in Linux. Although you set up proxy server in console, you couldn't connect internet over Google Chrome. So you open a command prompt(especially bash) and write this command:
linux@linux:~/$chromium-browser --proxy-server=*.*.*.*:*

*.*.*.*:* = your proxy server ip and port

How to check whether a string contains a substring in Ruby

If you look for a method in order to use while searching a string contains a substring, you could use this method;
a = "Skill"
if a.include? "ll"
    puts "exist"
end

How to get exact number in a string with using ruby

When I search a useful code block so as to find exact number in a string, I come accross this fruitful function in Ruby:

• str.delete("^0-9.")

error: device unauthorized. Please check the confirmation dialog on your device.

While encountering this error in linux shell, you could fix it by applying below instruction

•  unplug your device
• (in shell) SDK_DIR=(android_sdk_directory)
• cd $SDK_DIR/platform_tools
• ./adb start-server
• plug device
• confirm authorization

Convert pdf to image in linux

If you look for a tool in order to convert a pdf document to a image, you could use a useful command:

convert document.pdf document.png

this little tool come in handy very much.

Quick ntfs format in Linux

sudo mkfs.ntfs -f /dev/sdb1

NTFS is a journaling file system.Hence Don't forget unmount your disk before unplugged.

qemu-timer.o: undefined reference to symbol 'timer_settime@@GLIBC_2.3.3'

Another good solution is here while compiling qemu.

../.././gcc/libgcc.mvars: No such file or directory

This bug struggled me for a long time. Therefore, I found a good solution in here.

Fruitful Regex Hints

Minimum 8 characters at least 1 Alphabet and 1 Number:

"^(?=.*[A-Za-z])(?=.*\d)[A-Za-z\d]{8,}$"
 
Minimum 8 characters at least 1 Alphabet, 1 Number and 1 Special Character:

"^(?=.*[A-Za-z])(?=.*\d)(?=.*[$@$!%*#?&])[A-Za-z\d$@$!%*#?&]{8,}$"

Minimum 8 characters at least 1 Uppercase Alphabet, 1 Lowercase Alphabet and 1 Number:
 
"^(?=.*[a-z])(?=.*[A-Z])(?=.*\d)[a-zA-Z\d]{8,}$"


Minimum 8 characters at least 1 Uppercase Alphabet, 1 Lowercase Alphabet, 1 Number and 1 Special Character:

"^(?=.*[a-z])(?=.*[A-Z])(?=.*\d)(?=.*[$@$!%*?&])[A-Za-z\d$@$!%*?&]{8,}"


Minimum 8 and Maximum 10 characters at least 1 Uppercase Alphabet, 1 Lowercase Alphabet, 1 Number and 1 Special Character:
 
"^(?=.*[a-z])(?=.*[A-Z])(?=.*\d)(?=.*[$@$!%*?&])[A-Za-z\d$@$!%*?&]{8,10}"

How to monitor the services in Ubuntu 14.10

To oversee ubuntu linux background daemons, following command is fruitful:
sudo initctl list

There is a detailed explanation for this init control tool in here 

Ruby Quick Reference

When hacking Ruby on Rails, Some strange code stick in my mind. Therefore, while searching good guide, I found this useful Ruby reference.

Ubuntu 14.10 MATE nm-applet appearing problem

When you install a new Ubuntu 14.10 MATE, you couldn't see network manager applet in your top panel. To be enable it, you should edit /etc/xdg/autostart/nm-applet.desktop
[Desktop Entry]
Name=Network
Comment=Manage your network connections
Icon=nm-device-wireless
Exec=nm-applet
Terminal=false
Type=Application
NoDisplay=true
NotShowIn=KDE;
X-GNOME-Bugzilla-Bugzilla=GNOME
X-GNOME-Bugzilla-Product=NetworkManager
X-GNOME-Bugzilla-Component=nm-applet
X-GNOME-UsesNotifications=true
#AutostartCondition=GNOME3 unless-session gnome <---Comment out

X-Ubuntu-Gettext-Domain=nm-applet

Furthermore, if you run below instructions in your terminal, you will enable nm-applet every log in.

mkdir -v ~/.config/autostart

cp /etc/xdg/autostart/nm-applet.desktop ~/.config/autostart

How to set/unset git proxy

To set proxy server with git:

http_proxy=http://$server_ip:$server_port/
git config --global http.proxy $http_proxy

To unset proxy server with git:

git config --global --unset $http_proxy