Color Transparency in Android

Hex Opacity Values

100% — FF
95% — F2
90% — E6
85% — D9
80% — CC
75% — BF
70% — B3
65% — A6
60% — 99
55% — 8C
50% — 80
45% — 73
40% — 66
35% — 59
30% — 4D
25% — 40
20% — 33
15% — 26
10% — 1A
5% — 0D
0% — 00


For Ex:

Let's say you have a black color and you want to apply a 80% opacity on it.

Black - #000000

80% opacity - CC

Format: 

Opacity + Color

It would be:

#CC000000

Android - BroadcastReceiver when wifi or 3g network state changed

You need to set a permissions on android manifest

<uses-permission android:name="android.permission.ACCESS_NETWORK_STATE"/>

Set up your receiver

<receiver android:name=".NetworkChangeReceiver" >

            <intent-filter>

                <action android:name="android.net.conn.CONNECTIVITY_CHANGE" />

            </intent-filter>

</receiver>

Receiver code

import android.content.BroadcastReceiver;

import android.content.Context;

import android.content.Intent;

import android.net.ConnectivityManager;

import android.net.NetworkInfo;

import android.util.Log;

public class NetworkChangeReceiver extends BroadcastReceiver {

    @Override

    public void onReceive(Context context, Intent intent) {

    ConnectivityManager connMgr = (ConnectivityManager) context.getSystemService(Context.CONNECTIVITY_SERVICE);

        NetworkInfo wifi = connMgr.getNetworkInfo(ConnectivityManager.TYPE_WIFI);

        NetworkInfo mobile = connMgr.getNetworkInfo(ConnectivityManager.TYPE_MOBILE);

        boolean isConnected = wifi != null && wifi.isConnectedOrConnecting() || mobile != null && mobile.isConnectedOrConnecting(); 

        if (isConnected) {

            Log.d("Network Available ", "YES");

        }else{

           Log.d("Network Available ", "NO");

        }

    }

}

Convert binary image to image file

String strBinary = "binary data";
byte[] imageBytes= Base64.decodeBase64(strBinary.getBytes());
InputStream in = new ByteArrayInputStream(imageBytes);
Bitmap b = BitmapFactory.decodeStream(in);

Rails 1.9.2 , Carrierwave and RMagick Problem (Segmentation fault)

If you are homebrew users:
brew install -f imagemagick --disable-openmp

Note:
If you have imagemagick installed already, you need to remove it before you do the code above:

brew remove imagemagick
rm -rf `brew --cache imagemagick`


The following codes are the problem logs.

config.ru:229: [BUG] Segmentation fault
ruby 1.9.1p376 (2009-12-07 revision 26041) [i386-darwin10.3.0]

-- control frame ----------
c:0042 p:---- s:0196 b:0196 l:000195 d:000195 CFUNC :read
c:0041 p:0121 s:0192 b:0192 l:001ab8 d:000191 LAMBDA config.ru:229
c:0040 p:---- s:0189 b:0189 l:000188 d:000188 FINISH
c:0039 p:---- s:0187 b:0187 l:000186 d:000186 CFUNC :call
c:0038 p:0018 s:0184 b:0184 l:001d78 d:000183 BLOCK /usr/local/lib/ruby/gems/1.9.1/gems/sinatra-1.0/lib/sinatra/base.rb:865
c:0037 p:---- s:0182 b:0182 l:000181 d:000181 FINISH
c:0036 p:---- s:0180 b:0180 l:000179 d:000179 CFUNC :instance_eval
c:0035 p:0016 s:0177 b:0175 l:000174 d:000174 METHOD /usr/local/lib/ruby/gems/1.9.1/gems/sinatra-1.0/lib/sinatra/base.rb:521
c:0034 p:0024 s:0171 b:0171 l:000148 d:000170 BLOCK /usr/local/lib/ruby/gems/1.9.1/gems/sinatra-1.0/lib/sinatra/base.rb:500
c:0033 p:---- s:0169 b:0169 l:000168 d:000168 FINISH
c:0032 p:---- s:0167 b:0167 l:000166 d:000166 CFUNC :catch
c:0031 p:0140 s:0163 b:0163 l:000148 d:000162 BLOCK /usr/local/lib/ruby/gems/1.9.1/gems/sinatra-1.0/lib/sinatra/base.rb:497
c:0030 p:---- s:0154 b:0154 l:000153 d:000153 FINISH
c:0029 p:---- s:0152 b:0152 l:000151 d:000151 CFUNC :each
c:0028 p:0073 s:0149 b:0149 l:000148 d:000148 METHOD /usr/local/lib/ruby/gems/1.9.1/gems/sinatra-1.0/lib/sinatra/base.rb:476
c:0027 p:0076 s:0141 b:0141 l:000140 d:000140 METHOD /usr/local/lib/ruby/gems/1.9.1/gems/sinatra-1.0/lib/sinatra/base.rb:601
c:0026 p:0009 s:0137 b:0137 l:000138 d:000136 BLOCK /usr/local/lib/ruby/gems/1.9.1/gems/sinatra-1.0/lib/sinatra/base.rb:411
c:0025 p:---- s:0135 b:0135 l:000134 d:000134 FINISH
c:0024 p:---- s:0133 b:0133 l:000132 d:000132 CFUNC :instance_eval
c:0023 p:0012 s:0130 b:0130 l:000121 d:000129 BLOCK /usr/local/lib/ruby/gems/1.9.1/gems/sinatra-1.0/lib/sinatra/base.rb:566
c:0022 p:---- s:0128 b:0128 l:000127 d:000127 FINISH
c:0021 p:---- s:0126 b:0126 l:000125 d:000125 CFUNC :catch
c:0020 p:0013 s:0122 b:0122 l:000121 d:000121 METHOD /usr/local/lib/ruby/gems/1.9.1/gems/sinatra-1.0/lib/sinatra/base.rb:566
c:0019 p:0098 s:0115 b:0115 l:000138 d:000138 METHOD /usr/local/lib/ruby/gems/1.9.1/gems/sinatra-1.0/lib/sinatra/base.rb:411
c:0018 p:0019 s:0108 b:0108 l:000107 d:000107 METHOD /usr/local/lib/ruby/gems/1.9.1/gems/sinatra-1.0/lib/sinatra/base.rb:399
c:0017 p:0014 s:0104 b:0104 l:000103 d:000103 METHOD /usr/local/lib/ruby/gems/1.9.1/gems/rack-1.1.0/lib/rack/showexceptions.rb:24
c:0016 p:0150 s:0098 b:0098 l:000097 d:000097 METHOD /usr/local/lib/ruby/gems/1.9.1/gems/rack-1.1.0/lib/rack/methodoverride.rb:24
c:0015 p:0031 s:0092 b:0092 l:000091 d:000091 METHOD /usr/local/lib/ruby/gems/1.9.1/gems/rack-1.1.0/lib/rack/commonlogger.rb:18
c:0014 p:0018 s:0084 b:0084 l:002080 d:000083 BLOCK /usr/local/lib/ruby/gems/1.9.1/gems/sinatra-1.0/lib/sinatra/base.rb:979
c:0013 p:0032 s:0082 b:0082 l:000081 d:000081 METHOD /usr/local/lib/ruby/gems/1.9.1/gems/sinatra-1.0/lib/sinatra/base.rb:1005
c:0012 p:0011 s:0078 b:0078 l:002080 d:002080 METHOD /usr/local/lib/ruby/gems/1.9.1/gems/sinatra-1.0/lib/sinatra/base.rb:979
c:0011 p:0100 s:0074 b:0074 l:000ff0 d:000ff0 METHOD /usr/local/lib/ruby/gems/1.9.1/gems/rack-1.1.0/lib/rack/lint.rb:47
c:0010 p:0022 s:0068 b:0068 l:000067 d:000067 METHOD /usr/local/lib/ruby/gems/1.9.1/gems/rack-1.1.0/lib/rack/lint.rb:35
c:0009 p:0014 s:0064 b:0064 l:000063 d:000063 METHOD /usr/local/lib/ruby/gems/1.9.1/gems/rack-1.1.0/lib/rack/showexceptions.rb:24
c:0008 p:0031 s:0058 b:0058 l:000057 d:000057 METHOD /usr/local/lib/ruby/gems/1.9.1/gems/rack-1.1.0/lib/rack/commonlogger.rb:18
c:0007 p:0014 s:0050 b:0050 l:000049 d:000049 METHOD /usr/local/lib/ruby/gems/1.9.1/gems/rack-1.1.0/lib/rack/content_length.rb:13
c:0006 p:0320 s:0042 b:0042 l:000041 d:000041 METHOD /usr/local/lib/ruby/gems/1.9.1/gems/rack-1.1.0/lib/rack/handler/webrick.rb:48
c:0005 p:0256 s:0030 b:0030 l:000029 d:000029 METHOD /usr/local/lib/ruby/1.9.1/webrick/httpserver.rb:111
c:0004 p:0382 s:0020 b:0020 l:000019 d:000019 METHOD /usr/local/lib/ruby/1.9.1/webrick/httpserver.rb:70
c:0003 p:0123 s:0009 b:0009 l:000bc8 d:000008 BLOCK /usr/local/lib/ruby/1.9.1/webrick/server.rb:183
c:0002 p:---- s:0004 b:0004 l:000003 d:000003 FINISH
c:0001 p:---- s:0002 b:0002 l:000001 d:000001 TOP
---------------------------
-- Ruby level backtrace information-----------------------------------------
config.ru:229:in `read'
config.ru:229:in `block (2 levels) in

'
/usr/local/lib/ruby/gems/1.9.1/gems/sinatra-1.0/lib/sinatra/base.rb:865:in `call'
/usr/local/lib/ruby/gems/1.9.1/gems/sinatra-1.0/lib/sinatra/base.rb:865:in `block in route'
/usr/local/lib/ruby/gems/1.9.1/gems/sinatra-1.0/lib/sinatra/base.rb:521:in `instance_eval'
/usr/local/lib/ruby/gems/1.9.1/gems/sinatra-1.0/lib/sinatra/base.rb:521:in `route_eval'
/usr/local/lib/ruby/gems/1.9.1/gems/sinatra-1.0/lib/sinatra/base.rb:500:in `block (2 levels) in route!'
/usr/local/lib/ruby/gems/1.9.1/gems/sinatra-1.0/lib/sinatra/base.rb:497:in `catch'
/usr/local/lib/ruby/gems/1.9.1/gems/sinatra-1.0/lib/sinatra/base.rb:497:in `block in route!'
/usr/local/lib/ruby/gems/1.9.1/gems/sinatra-1.0/lib/sinatra/base.rb:476:in `each'
/usr/local/lib/ruby/gems/1.9.1/gems/sinatra-1.0/lib/sinatra/base.rb:476:in `route!'
/usr/local/lib/ruby/gems/1.9.1/gems/sinatra-1.0/lib/sinatra/base.rb:601:in `dispatch!'
/usr/local/lib/ruby/gems/1.9.1/gems/sinatra-1.0/lib/sinatra/base.rb:411:in `block in call!'
/usr/local/lib/ruby/gems/1.9.1/gems/sinatra-1.0/lib/sinatra/base.rb:566:in `instance_eval'
/usr/local/lib/ruby/gems/1.9.1/gems/sinatra-1.0/lib/sinatra/base.rb:566:in `block in invoke'
/usr/local/lib/ruby/gems/1.9.1/gems/sinatra-1.0/lib/sinatra/base.rb:566:in `catch'
/usr/local/lib/ruby/gems/1.9.1/gems/sinatra-1.0/lib/sinatra/base.rb:566:in `invoke'
/usr/local/lib/ruby/gems/1.9.1/gems/sinatra-1.0/lib/sinatra/base.rb:411:in `call!'
/usr/local/lib/ruby/gems/1.9.1/gems/sinatra-1.0/lib/sinatra/base.rb:399:in `call'
/usr/local/lib/ruby/gems/1.9.1/gems/rack-1.1.0/lib/rack/showexceptions.rb:24:in `call'
/usr/local/lib/ruby/gems/1.9.1/gems/rack-1.1.0/lib/rack/methodoverride.rb:24:in `call'
/usr/local/lib/ruby/gems/1.9.1/gems/rack-1.1.0/lib/rack/commonlogger.rb:18:in `call'
/usr/local/lib/ruby/gems/1.9.1/gems/sinatra-1.0/lib/sinatra/base.rb:979:in `block in call'
/usr/local/lib/ruby/gems/1.9.1/gems/sinatra-1.0/lib/sinatra/base.rb:1005:in `synchronize'
/usr/local/lib/ruby/gems/1.9.1/gems/sinatra-1.0/lib/sinatra/base.rb:979:in `call'
/usr/local/lib/ruby/gems/1.9.1/gems/rack-1.1.0/lib/rack/lint.rb:47:in `_call'
/usr/local/lib/ruby/gems/1.9.1/gems/rack-1.1.0/lib/rack/lint.rb:35:in `call'
/usr/local/lib/ruby/gems/1.9.1/gems/rack-1.1.0/lib/rack/showexceptions.rb:24:in `call'
/usr/local/lib/ruby/gems/1.9.1/gems/rack-1.1.0/lib/rack/commonlogger.rb:18:in `call'
/usr/local/lib/ruby/gems/1.9.1/gems/rack-1.1.0/lib/rack/content_length.rb:13:in `call'
/usr/local/lib/ruby/gems/1.9.1/gems/rack-1.1.0/lib/rack/handler/webrick.rb:48:in `service'
/usr/local/lib/ruby/1.9.1/webrick/httpserver.rb:111:in `service'
/usr/local/lib/ruby/1.9.1/webrick/httpserver.rb:70:in `run'
/usr/local/lib/ruby/1.9.1/webrick/server.rb:183:in `block in start_thread'

-- C level backtrace information -------------------------------------------
0x10010cd8d 0 libruby.dylib 0x000000010010cd8d rb_vm_bugreport + 77
0x10002b184 1 libruby.dylib 0x000000010002b184 report_bug + 260
0x10002b318 2 libruby.dylib 0x000000010002b318 rb_bug + 200
0x1000b7124 3 libruby.dylib 0x00000001000b7124 sigsegv + 132
0x7fff8301c80a 4 libSystem.B.dylib 0x00007fff8301c80a _sigtramp + 26
0x1032313ac 5 libMagickCore.3.dylib 0x00000001032313ac Splay + 300
0x103119245 6 libMagickCore.3.dylib 0x0000000103119245 AcquirePixelCache + 325
0x1031cb317 7 libMagickCore.3.dylib 0x00000001031cb317 AcquireImage + 375
0x10333035b 8 libMagickCore.3.dylib 0x000000010333035b ReadPNGImage + 155
0x1031418fd 9 libMagickCore.3.dylib 0x00000001031418fd ReadImage + 2221
0x101f1b72b 10 RMagick2.bundle 0x0000000101f1b72b rd_image + 339
0x101f1b59b 11 RMagick2.bundle 0x0000000101f1b59b Image_read + 36
0x1000fd0e4 12 libruby.dylib 0x00000001000fd0e4 vm_call_cfunc + 340
0x1000fe9b0 13 libruby.dylib 0x00000001000fe9b0 vm_call_method + 896
0x1000ff8fc 14 libruby.dylib 0x00000001000ff8fc vm_exec_core + 3180
0x100104b93 15 libruby.dylib 0x0000000100104b93 vm_exec + 1203
0x100106643 16 libruby.dylib 0x0000000100106643 rb_vm_invoke_proc + 691
0x100106ccd 17 libruby.dylib 0x0000000100106ccd vm_call0 + 1085
0x1000317c6 18 libruby.dylib 0x00000001000317c6 rb_method_call + 406
0x1000fd0e4 19 libruby.dylib 0x00000001000fd0e4 vm_call_cfunc + 340
0x1000fe9b0 20 libruby.dylib 0x00000001000fe9b0 vm_call_method + 896
0x1000ff8fc 21 libruby.dylib 0x00000001000ff8fc vm_exec_core + 3180
0x100104b93 22 libruby.dylib 0x0000000100104b93 vm_exec + 1203
0x100105ce6 23 libruby.dylib 0x0000000100105ce6 yield_under + 710
0x100106188 24 libruby.dylib 0x0000000100106188 specific_eval + 72
0x1000fd0e4 25 libruby.dylib 0x00000001000fd0e4 vm_call_cfunc + 340
0x1000fe9b0 26 libruby.dylib 0x00000001000fe9b0 vm_call_method + 896
0x1000ff8fc 27 libruby.dylib 0x00000001000ff8fc vm_exec_core + 3180
0x100104b93 28 libruby.dylib 0x0000000100104b93 vm_exec + 1203
0x10010b6bf 29 libruby.dylib 0x000000010010b6bf rb_f_catch + 639
0x1000fd0e4 30 libruby.dylib 0x00000001000fd0e4 vm_call_cfunc + 340
0x1000fe9b0 31 libruby.dylib 0x00000001000fe9b0 vm_call_method + 896
0x1000ff8fc 32 libruby.dylib 0x00000001000ff8fc vm_exec_core + 3180
0x100104b93 33 libruby.dylib 0x0000000100104b93 vm_exec + 1203
0x10010aac9 34 libruby.dylib 0x000000010010aac9 rb_yield + 505
0x100007902 35 libruby.dylib 0x0000000100007902 rb_ary_each + 82
0x1000fd0e4 36 libruby.dylib 0x00000001000fd0e4 vm_call_cfunc + 340
0x1000fe9b0 37 libruby.dylib 0x00000001000fe9b0 vm_call_method + 896
0x1000ff8fc 38 libruby.dylib 0x00000001000ff8fc vm_exec_core + 3180
0x100104b93 39 libruby.dylib 0x0000000100104b93 vm_exec + 1203
0x100105ce6 40 libruby.dylib 0x0000000100105ce6 yield_under + 710
0x100106188 41 libruby.dylib 0x0000000100106188 specific_eval + 72
0x1000fd0e4 42 libruby.dylib 0x00000001000fd0e4 vm_call_cfunc + 340
0x1000fe9b0 43 libruby.dylib 0x00000001000fe9b0 vm_call_method + 896
0x1000ff8fc 44 libruby.dylib 0x00000001000ff8fc vm_exec_core + 3180
0x100104b93 45 libruby.dylib 0x0000000100104b93 vm_exec + 1203
0x10010b6bf 46 libruby.dylib 0x000000010010b6bf rb_f_catch + 639
0x1000fd0e4 47 libruby.dylib 0x00000001000fd0e4 vm_call_cfunc + 340
0x1000fe9b0 48 libruby.dylib 0x00000001000fe9b0 vm_call_method + 896
0x1000ff8fc 49 libruby.dylib 0x00000001000ff8fc vm_exec_core + 3180
0x100104b93 50 libruby.dylib 0x0000000100104b93 vm_exec + 1203
0x100106643 51 libruby.dylib 0x0000000100106643 rb_vm_invoke_proc + 691
0x100111803 52 libruby.dylib 0x0000000100111803 thread_start_func_2 + 835
0x100111921 53 libruby.dylib 0x0000000100111921 thread_start_func_1 + 17
0x7fff82ff58b6 54 libSystem.B.dylib 0x00007fff82ff58b6 _pthread_start + 331
0x7fff82ff5769 55 libSystem.B.dylib 0x00007fff82ff5769 thread_start + 13

[NOTE]
You may encounter a bug of Ruby interpreter. Bug reports are welcome.
For details: http://www.ruby-lang.org/bugreport.html

Abort trap

Uninitialized constant MysqlCompat::MysqlRes

Note: I'm using Mac OS X Version: 10.6.3

Open the Terminal.

First removed all mysql gems:

• gem uninstall mysql

After removing the mysql gem run the following:

sudo env ARCHFLAGS="-arch x86_64" gem install mysql -- --with-mysql-config=/usr/local/mysql/bin/mysql_config

Uninstall MySQL on Mac OS X

NOTE: This will delete all your databases.

Open the Terminal then do the following:

• sudo rm /usr/local/mysql
• sudo rm -rf /usr/local/mysql*
• sudo rm -rf /Library/StartupItems/MySQLCOM
• sudo rm -rf /Library/PreferencePanes/My*
• sudo rm -rf ~/Library/PreferencePanes/My*
• edit /etc/hostconfig and remove the line MYSQLCOM=-YES-
• sudo rm -rf /Library/Receipts/mysql*
• sudo rm -rf /Library/Receipts/MySQL*
• sudo rm -rf /var/db/receipts/com.mysql.*

J2ME String Split Method

private String[] split(String _text, String _separator) {
Vector nodes = new Vector();
// Parse nodes into vector
int index = _text.indexOf(_separator);

while (index >= 0) {
nodes.addElement(_text.substring(0, index));
_text = _text.substring(index + _separator.length());
index = _text.indexOf(_separator);
}
// Get the last node
nodes.addElement(_text);

// Create splitted string array
String[] result = new String[nodes.size()];
if (nodes.size() > 0) {
for (int loop = 0; loop < nodes.size(); loop++) {
result[loop] = (String) nodes.elementAt(loop);
System.out.println(result[loop]);
}
}
return result;
}

J2ME String Replace Method

J2ME doesn't have a replace method so you can use the code below. I found this function/method at http://www.itgalary.com/forum_posts.asp?TID=871 . I hope that you can use it too.

public static String replace(String _text, String _searchStr, String _replacementStr) {
// String buffer to store str
StringBuffer sb = new StringBuffer();

// Search for search
int searchStringPos = _text.indexOf(_searchStr);
int startPos = 0;
int searchStringLength = _searchStr.length();

// Iterate to add string
while (searchStringPos != -1) {
sb.append(_text.substring(startPos, searchStringPos)).append(_replacementStr);
startPos = searchStringPos + searchStringLength;
searchStringPos = _text.indexOf(_searchStr, startPos);
}

// Create string
sb.append(_text.substring(startPos,_text.length()));

return sb.toString();
}

Ruby on Rails Installation on Windows

1. Download ruby186-25.exe at rubyinstaller.rubyforge.org
2. Install it.
3. First, let's check to see if you already have Ruby installed.
   Bring up a command prompt and type ruby -v.
4. With RubyGems loaded, you can install all of Rails and its dependencies through the command line: C:\> gem install rails --include-dependencies

Keeping Rails Up-to-Date:
C:\> gem update rails

PHP Tutorial with XAMPP for Windows

Introduction

PHP is a powerful tool for making dynamic and interactive Web pages.

It is the widely-used, free, and efficient alternative to competitors such as Microsoft's ASP and other scripting languages.

In our tutorial you will learn about PHP, and how to execute scripts on your server.

XAMPP is an easy to install Apache distribution containing MySQL, PHP and Perl. XAMPP is really very easy to install and to use - just download, extract and start.

What is PHP?

• PHP stands for PHP: Hypertext Preprocessor
• PHP is a server-side scripting language, like Ruby on Rails, ASP, JSP and others
  
• PHP scripts are executed on the server
• PHP is an open source software
• PHP supports many databases (MySQL, Oracle, PostgreSQL and etc.)
• PHP is free to download and use
• PHP files have a file extension of ".php" or ".php3"

Why PHP?

• PHP runs on different platforms (Windows, Linux, Unix, etc.)
• PHP is compatible with almost all servers used today (Apache, IIS, etc.)
• PHP is FREE to download at www.php.net
• PHP is easy to learn and runs efficiently on the server side

What do you Need?

• Any Text Editor like Notepad, Notepad++ and E
• Download XAMPP for Windows at http://www.apachefriends.org/en/xampp-windows.html then install it just follow the installation wizard.

Note: The default installation directory is C:\xampp and C:\xampp\htdocs is the location for the PHP file.


How to Run a PHP file using XAMPP?

• Create a PHP file then save it to C:\xampp\htdocs directory.
• Open your browser then type "http://localhost/Your PHP File name" or "http://I.P. Address/Your PHP File name"

Basic PHP Syntax

A PHP scripting block always starts with <?php and ends with ?>. A PHP scripting block can be placed anywhere in the document.

Example:

<?php
//Put your code here
?>

A PHP file normally contains HTML tags, Javascript and PHP scripting code.

Example:

<html>
<body>

<?php
echo " Hello World ";
?>

</body>
</html>

Each code line in PHP must end with a semicolon. The semicolon is a separator and is used to distinguish one set of instructions from another.

Note: The file must have a .php or .php3 extension else the PHP code will not be executed.


Comments in PHP

• // to make a single-line comment
• /* and */ to make a large comment block.

Example:

<html>
<body>

<?php

//This is a comment

/*
This is
a comment
block
*/

?>

</body>
</html>

Variable Declarations in PHP

Variables are used for storing a values, like text strings, numbers or arrays.
In PHP, a variable does not need to be declared before adding a value to it and no data type needed, PHP will automatically converts the variable to the correct data type, depending on its value.

PHP variables are start with a $ sign symbol.

Example:

$variable_name = value;

Naming Rules for PHP Variables

• A variable name must start with a letter or an underscore "_"
• A variable name should not contain spaces.
• A variable name can only contain alpha-numeric characters and underscores (a-z, A-Z, 0-9, and _ )

Valid Example:

$variable_name
$VariableName
$varName
$varName1