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(+ (+ 4 3) ( - 3 2) 5)

Please insert an expression in the box above.
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Regular Expressions quick reference

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  • How do I match several test cases?
    This is easy! Use the ^$ anchors in your expressions, combined with the multine flag! This will treat each line in the textarea above as an independent 'test case' if you will.
  • Where can I read more about regular expressions?
    Besides the quiz here on the website I highly recommend http://www.regular-expressions.info/. Another great read is the Mastering Regular Expressions which, unfortunately, is not free. If you have a few minutes to waste, check out regexcrossword.com
  • What does the numbers [m-n] mean in the Match groups?
    There numbers show the start and end offset (in bytes) respectively where the engine found the result.
  • Can I save or share my work?
    You can always create a permalink and use it in any way you like. Creating a permalink will store your data to a database, make sure you read the privacy policy if this concerns you. If you're up for it, submit it to the community
Understanding lookarounds
Lookbehinds are fixed width, meaning you can not use any quantifiers (+, ?, *, {m,n}). Lookarounds are also zero-width assertions. In other words, they do not consume what they match. Play around with thte debugger to see how this works in real life.

Understanding lookarounds with babewatching
With (?=babe) you only see them when they are right in front of you. With (?=.*babe) you'll see them even when they are far away. And finally with (?<=babe) you'll only see them when they are directly behind you.
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