As the first online Regular Expression tester to offer realtime highlighting and offering more languages than any other online tester, ReJAx continues to be the coolest and easiest to use Regular Expression tester on the web. Supported languages:
    * JavaScript
    * PHP 5 PCRE
    * PHP 5 POSIX
    * Ruby - BETA!!
    * PERL 5
    * UNIX Shell Pattern
It is not necessary to enter the beginning and ending slashes in the pattern field. Not all modifiers will be compatible with every language. Backreferences (when available) are usually in the form of \n where n is the reference number

Features:

• You can enter statements and expressions at the same prompt.


• The result of each non-void statement or expression is shown.


• User-defined variables.
  
  
  
  • b = document.body
  
  
  
  


• User-defined functions.
  
  
  
  • function f() { return 5; }
  
  
  
  


• JavaScript error messages are shown in red.


• Previous statements and expressions are available through Up and Down arrow keys.


• Tab completion.


• Multiline input (Shift+Enter to insert a line break).


• If the shell is opened using a bookmarklet, JavaScript typed into the shell runs in the context of the original window.


• Works well in Firefox, mostly works in Opera 8 and in IE 6 for Windows.

Suggested uses:

• Test short bits of JavaScript, bookmarklets, or user scripts. (For longer bits of JavaScript, try the JavaScript development enviornment too.)


• Explore DOM objects such as document.body using props (Alt+P) to figure out what is possible.


• Explore the DOM of a specific page using the bookmarklet version of the shell.


• Modify the DOM of a specific page using the bookmarklet version of the shell.


• Use the shell like you would use the home screen of a calculator such as a TI-83. Alt+M gives you easy access to math functions such as sin and pow.