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  • If you had to reinvent a new syntax for regular expressions, what would it look like?

    - by Timwi
    Regular expressions as they are today are pretty much as concise and compact as they can be. Consequently, they are often criticised for being unreadable and hard to debug. If you had to reinvent a new syntax for regular expressions, what would it look like? Do you prefer the concise syntax they already have (or a different but similarly concise syntax)? If so, please justify why you think regular expressions deserve to be this concise, but your favourite programming language doesn’t (unless it’s Perl). Or do you think regular expressions should have a slightly more spaced-out syntax and look a bit more like operators and syntax elements normally do in programming languages? If so, provide examples of what you think the syntax should look like, and justify why it is better than the current syntax. Or do you think there shouldn’t even be a special syntax for regular expressions, and instead they should be constructed from syntax elements already present in the programming language? If so, give examples of a syntax that might be used to construct such regular expressions.

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  • Using Find/Replace with regular expressions inside a SSIS package

    - by jamiet
    Another one of those might-be-useful-again-one-day-so-I’ll-share-it-in-a-blog-post blog posts I am currently working on a SQL Server Integration Services (SSIS) 2012 implementation where each package contains a parameter called ETLIfcHist_ID: During normal execution this will get altered when the package is executed from the Execute Package Task however we want to make sure that at deployment-time they all have a default value of –1. Of course, they tend to get changed during development so I wanted a way of easily changing them all back to the default value. Opening up each package in turn and editing them was an option but given that we have over 40 packages and we might want to carry out this reset fairly frequently I needed a more automated method so I turned to Visual Studio’s Find/Replace… feature Of course, we don’t know what value will be in that parameter so I can’t simply search for a particular value; hence I opted to use a regular expression to identify the value to be change. In the rest of this blog post I’ll explain how to do that. For demonstration purposes I have taken the contents of a .dtsx file and stripped out everything except the element containing the parameters (<DTS:PackageParameters>), if you want to play along at home you can copy-paste the XML document below into a new XML file and open it up in Visual Studio: <?xml version="1.0"?> <DTS:Executable xmlns:DTS="www.microsoft.com/SqlServer/Dts">   <DTS:PackageParameters>     <DTS:PackageParameter       DTS:CreationName=""       DTS:DataType="3"       DTS:Description="InterfaceHistory_ID: used for Lineage"       DTS:DTSID="{635616DB-EEEE-45C8-89AA-713E25846C7E}"       DTS:ObjectName="ETLIfcHist_ID">       <DTS:Property         DTS:DataType="3"         DTS:Name="ParameterValue">VALUE_TO_BE_CHANGED</DTS:Property>     </DTS:PackageParameter>     <DTS:PackageParameter       DTS:CreationName=""       DTS:DataType="3"       DTS:Description="Some other description"       DTS:DTSID="{635616DB-EEEE-45C8-89AA-713E25845C7E}"       DTS:ObjectName="SomeOtherObjectName">       <DTS:Property         DTS:DataType="3"         DTS:Name="ParameterValue">SomeOtherValue</DTS:Property>     </DTS:PackageParameter>   </DTS:PackageParameters> </DTS:Executable> We are trying to identify the value of the parameter whose name is ETLIfcHist_ID – notice that in the XML document above that value is VALUE_TO_BE_CHANGED. The following regular expression will find the appropriate portion of the XML document: {\<DTS\:PackageParameter[\n ]*DTS\:CreationName="[A-Za-z0-9\:_\{\}- ]*"[\n ]*DTS\:DataType="[A-Za-z0-9\:_\{\}- ]*"[\n ]*DTS\:Description="[A-Za-z0-9\:_\{\}- ]*"[\n ]*DTS\:DTSID="[A-Za-z0-9\:_\{\}- ]*"[\n ]*DTS\:ObjectName="ETLIfcHist_ID"\>[\n ]*\<DTS\:Property[\n ]*DTS\:DataType="[A-Za-z0-9\:_\{\}- ]*"[\n ]*DTS\:Name="ParameterValue"\>}[A-Za-z0-9\:_\{\}- ]*{\<\/DTS\:Property\>} I have highlighted the name of the parameter that we’re looking for. I have also highlighted two portions identified by pairs of curly braces “{…}”; these are important because they pick out the two portions either side of the value I want to replace, in other words the portions highlighted here: <DTS:PackageParameters>     <DTS:PackageParameter       DTS:CreationName=""       DTS:DataType="3"       DTS:Description="InterfaceHistory_ID: used for Lineage"       DTS:DTSID="{635616DB-EEEE-45C8-89AA-713E25846C7E}"       DTS:ObjectName="ETLIfcHist_ID">       <DTS:Property         DTS:DataType="3"         DTS:Name="ParameterValue">VALUE_TO_BE_CHANGED</DTS:Property>     </DTS:PackageParameter> Those sections in the curly braces are termed tag expressions and can be identified in the replace expression using a backslash and a number identifying which tag expression you’re referring to according to its ordinal position. Hence, our replace expression is simply: \1-1\2 We’re saying the portion of our file identified by the regular expression should be replaced by the first curly brace section, then the literal –1, then the second curly brace section. Make sense? Give it a go yourself by plugging those two expressions into Visual Studio’s Find and Replace dialog. If you set it to look in “All Open Documents” then you can open up the code-behind of all your packages and change all of them at once. The Find and Replace dialog will look like this: That’s it! I realise that not everyone will be looking to change the value of a parameter but hopefully I have shown you a technique that you can modify to work for your own scenario. Given that this blog post is, y’know, on the web I have no doubt that someone is going to find a fault with my find regex expression and if that person is you….that’s OK. Let me know about it in the comments below and perhaps we can work together to come up with something better! Note that some parameters may have a different set of properties (for example some, but not all, of my parameters have a DTS:Required attribute) so your find regular expression may have to change accordingly. When researching this I found the following article to be invaluable: Visual Studio Find/Replace Regular Expression Usage @Jamiet

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  • Compute Scalars, Expressions and Execution Plan Performance

    - by Paul White
    The humble Compute Scalar is one of the least well-understood of the execution plan operators, and usually the last place people look for query performance problems. It often appears in execution plans with a very low (or even zero) cost, which goes some way to explaining why people ignore it. Some readers will already know that a Compute Scalar can contain a call to a user-defined function, and that any T-SQL function with a BEGIN…END block in its definition can have truly disastrous consequences...(read more)

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  • Regular Expressions. Remember it, write it, test it.

    - by outcoldman
    I should say that I’m fan of regular expressions. Whenever I see the problem, which I can solve with Regex, I felt a burning desire to do it and going to write new test for new regex. Previously I had installed SharpDevelop Studio just for good regular expression tool in it (Why VS doesn’t have one?). But now I’m a little wiser, and for each Regex I write a separate test. I find it difficult to remember the syntax of regular expressions (I don’t write them very often); I always forget which character is responsible for the beginning of the line, etc. So I use external small and easy articles like this “Regular expressions - An introduction”. Now I want to show you little samples of regular expressions and want to show you how to test these samples. Read more... (redirect to http://outcoldman.ru)

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  • What’s New in The Second Edition of Regular Expressions Cookbook

    - by Jan Goyvaerts
    %COOKBOOKFRAME% The second edition of Regular Expressions Cookbook is a completely revised edition, not just a minor update. All of the content from the first edition has been updated for the latest versions of the regular expression flavors and programming languages we discuss. We’ve corrected all errors that we could find and rewritten many sections that were either unclear or lacking in detail. And lack of detail was not something the first edition was accused of. Expect the second edition to really dot all i’s and cross all t’s. A few sections were removed. In particular, we removed much talk about browser inconsistencies as modern browsers are much more compatible with the official JavaScript standard. There is plenty of new content. The second edition has 101 more pages, bringing the total to 612. It’s almost 20% bigger than the first edition. We’ve added XRegExp as an additional regex flavor to all recipes throughout the book where XRegExp provides a better solution than standard JavaScript. We did keep the standard JavaScript solutions, so you can decide which is better for your needs. The new edition adds 21 recipes, bringing the total to 146. 14 of the new recipes are in the new Source Code and Log Files chapter. These recipes demonstrate techniques that are very useful for manipulating source code in a text editor and for dealing with log files using a grep tool. Chapter 3 which has recipes for programming with regular expressions gets only one new recipe, but it’s a doozy. If anyone has ever flamed you for using a regular expression instead of a parser, you’ll now be able to tell them how you can create your own parser by mixing regular expressions with procedural code. Combined with the recipes from the new Source Code and Log Files chapter, you can create parsers for whatever custom language or file format you like. If you have any interest in regular expressions at all, whether you’re a beginner or already consider yourself an expert, you definitely need a copy of the second edition of Regular Expressions Cookbook if you didn’t already buy the first. If you did buy the first edition, and you often find yourself referring back to it, then the second edition is a very worthwhile upgrade. You can buy the second edition of Regular Expressions Cookbook from Amazon or wherever technical books are sold. Ask for ISBN 1449319432.

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  • regular expressions: love or hate or alternatives?

    - by yamspog
    While I can see the value and usefulness of regular expressions, I also find that they are extremely complicated and difficult to create and debug. I am often at the point where I find their usefulness is offset by the difficulty in creating expressions. I am a bit astonished by the fact that there is nothing quite like them and that there hasn't been an effort to recreate them use a more verbose or less arcane syntax. so, are regular expressions here to stay? are there alternatives that are gaining traction? do other people just ignore them and write hundreds of lines of string compare functions?

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  • Lambda Expressions

    - by Asad Khan
    Can somebody explain me lambda expressions & what they can be used for. I have googled for it & have a rough idea. most of the examples give c# code. How about lambda expressions in plain old C...?

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  • Windows: File copy/move with filename regular expressions?

    - by Ian Boyd
    i basically want to run: C:\>xcopy [0-9]{13}\.(gif|jpg|png) s:\TargetFolder /s i know xcopy doesn't support regular-express filename searches. i can't find out how to find out if PowerShell has a Cmdlet to copy files; and if it does, how to find out if it supports regular expression filename matching. Can anyone think of a way to perform a recursive file copy/move with regex filename matching?

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  • How to Process Lambda Expressions Passed as Argument Into Method - C# .NET 3.5

    - by Sunday Ironfoot
    My knowledge of Lambda expressions is a bit shaky, while I can write code that uses Lambda expressions (aka LINQ), I'm trying to write my own method that takes a few arguments that are of type Lambda Expression. Background: I'm trying to write a method that returns a Tree Collection of objects of type TreeItem from literally ANY other object type. I have the following so far: public class TreeItem { public string Id { get; set; } public string Text { get; set; } public TreeItem Parent { get; protected set; } public IList<TreeItem> Children { get { // Implementation that returns custom TreeItemCollection type } } public static IList<TreeItem> GetTreeFromObject<T>(IList<T> items, Expression<Func<T, string>> id, Expression<Func<T, string>> text, Expression<Func<T, IList<T>>> childProperty) where T : class { foreach (T item in items) { // Errrm!?? What do I do now? } return null; } } ...which can be called via... IList<TreeItem> treeItems = TreeItem.GetTreeFromObject<Category>( categories, c => c.Id, c => c.Name, c => c.ChildCategories); I could replace the Expressions with string values, and just use reflection, but I'm trying to avoid this as I want to make it strongly typed. My reasons for doing this is that I have a control that accepts a List of type TreeItem, whereas I have dozens of different types that are all in a tree like structure, and don't want to write seperate conversion methods for each type (trying to adhere to the DRY principle). Am I going about this the right way? Is there a better way of doing this perhaps?

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  • Inspiring problems to show off the importance of regular expressions?

    - by ragu.pattabi
    I am planning to give a presentation/demonstration on regular expressions at work to encourage young developers to add this powerful and important tool in their toolbox. Just teaching syntax doesn't cut it. I often see people say nice. After the presentation, they get on with their programming lives without ever thinking of using it mostly. I am raking my grey matter to come up with some solid examples, not just problems that matches 'cat' and 'cut'. I missed to note down the occasions of my regex enlightenments to use here. :^( Do you have some inspiring problems to share that could be solved with regex?

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  • Can non-IT people learn and take advantage of regular expressions? [closed]

    - by user1598390
    Often times, not-IT people has to deal with massive text data, clean it, filter it, modify it. Often times normal office tools like Excel lack the tools to make complex search and replace operations on text. Could this people benefit from regexps ? Can regexp be taught to them ? Are regular expressions the exclusive domain of programmers and unix/linux technicians ? Can they be learned by non-IT people, given regexps are not a programming language? Is this a valid or achievable goal to make some users regexp-literate through appopriate training ? Have you have any experiences on this issue? and if so, have it been successful ?

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  • Regular Expressions Cookbook Code Samples

    - by Jan Goyvaerts
    %COOKBOOKFRAME% One of the common criticisms against the first edition was that we didn’t have the regular expressions and code samples available for download. Since our book only has very short code snippets rather than complete programs, we (the authors) did not have these available as separate files either. But for the second edition we’re trying to do better. You can now download the code samples from the 2nd edition of Regular Expressions Cookbook. This HTML file contains all the blocks with regular expressions and source code from the book, along with the titles of the chapters, recipes, and sections that they are found in. If you have purchased the book, you can use this file to easily copy and paste the regular expressions and source code snippets. Even if you purchased the ebook, you may prefer to use this file. The regexes in the ebook are formatted with line breaks and gray dots for spaces to make them easier to read in print. The HTML file does not use such formatting, so you can copy and paste them directly. This means that some very regexes will run beyond the edge of your browser window.

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  • Javascript to match a specific number using regular expressions

    - by ren33
    I was using javascript to detect for specific key strokes and while writing the method I thought I'd try regular expressions and the test() method and came up with: if (/8|9|37|38|46|47|48|49|50|51|52|53|54|55|56|57|96|97|98|99|100|101|102|103|104|105|110/.test(num)) { // do something if there's a match } This doesn't seem to work 100% as some values seem to make it past the regex test, such as 83. I've since moved on, but I'm still curious as to why this didn't work.

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  • PHP and Regular Expressions question?

    - by php
    I was wondering if the codes below are the correct way to check for a street address, email address, password, city and url using preg_match using regular expressions? And if not how should I fix the preg_match code? preg_match ('/^[A-Z0-9 \'.-]{1,255}$/i', $trimmed['address']) //street address preg_match ('/^[\w.-]+@[\w.-]+\.[A-Za-z]{2,6}$/', $trimmed['email'] //email address preg_match ('/^\w{4,20}$/', $trimmed['password']) //password preg_match ('/^[A-Z \'.-]{1,255}$/i', $trimmed['city']) //city preg_match("/^[a-zA-Z]+[:\/\/]+[A-Za-z0-9\-_]+\\.+[A-Za-z0-9\.\/%&=\?\-_]+$/i", $trimmed['url']) //url

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  • BASH Arithmetic Expressions

    - by Arko
    I had used several ways to do some simple integer arithmetic in BASH (3.2). But I can't figure out the best (preferred) way to do it. result=`expr 1 + 2` result=$(( 1 + 2 )) let "result = 1 + 2" What are the fundamental differences between those expressions? Is there other ways to do the same? Is the use of a tool like bc mandatory for floating point arithmetic? result=`echo "7/354" | bc`

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  • Lambda Expressions and Memory Management

    - by Surya
    How do the Lambda Expressions / Closures in C++0x complicate the memory management in C++? Why do some people say that closures have no place in languages with manual memory management? Is there claim valid and if yes, what are the reasons behind it?

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  • Formal Languages, Inductive Proofs &amp; Regular Expressions

    - by MarkPearl
    So I am slogging away at my UNISA stuff. I have just finished doing the initial once non stop read through the first 11 chapters of my COS 201 Textbook - “Introduction to Computer Theory 2nd Edition” by Daniel Cohen. It has been an interesting couple of days, with familiar concepts coming up as well as some new territory. In this posting I am going to cover the first couple of chapters of the book. Let start with Formal Languages… What exactly is a formal language? Pretty much a no duh question for me but still a good one to ask – a formal language is a language that is defined in a precise mathematical way. Does that mean that the English language is a formal language? I would say no – and my main motivation for this is that one can have an English sentence that is correct grammatically that is also ambiguous. For example the ambiguous sentence: "I once shot an elephant in my pyjamas.” For this and possibly many other reasons that I am unaware of, English is termed a “Natural Language”. So why the importance of formal languages in computer science? Again a no duh question in my mind… If we want computers to be effective and useful tools then we need them to be able to evaluate a series of commands in some form of language that when interpreted by the device no confusion will exist as to what we were requesting. Imagine the mayhem that would exist if a computer misinterpreted a command to print a document and instead decided to delete it. So what is a Formal Language made up of… For my study purposes a language is made up of a finite alphabet. For a formal language to exist there needs to be a specification on the language that will describe whether a string of characters has membership in the language or not. There are two basic ways to do this: By a “machine” that will recognize strings of the language (e.g. Finite Automata). By a rule that describes how strings of a language can be formed (e.g. Regular Expressions). When we use the phrase “string of characters”, we can also be referring to a “word”. What is an Inductive Proof? So I am not to far into my textbook and of course it starts referring to proofs and different types. I have had to go through several different approaches of proofs in the past, but I can never remember their formal names , so when I saw “inductive proof” I thought to myself – what the heck is that? Google to the rescue… An inductive proof is like a normal proof but it employs a neat trick which allows you to prove a statement about an arbitrary number n by first proving it is true when n is 1 and then assuming it is true for n=k and showing it is true for n=k+1. The idea is that if you want to show that someone can climb to the nth floor of a fire escape, you need only show that you can climb the ladder up to the fire escape (n=1) and then show that you know how to climb the stairs from any level of the fire escape (n=k) to the next level (n=k+1). Does this sound like a form of recursion? No surprise then that in the same chapter they deal with recursive definitions. An example of a recursive definition for the language EVEN would the 3 rules below: 2 is in EVEN If x is in EVEN then so is x+2 The only elements in the set EVEN are those that be produced by the rules above. Nothing to exciting… So if a definition for a language is done recursively, then it makes sense that the language can be proved using induction. Regular Expressions So I am wondering to myself what use is this all – in fact – I find this the biggest challenge to any university material is that it is quite hard to find the immediate practical applications of some theory in real life stuff. How great was my joy when I suddenly saw the word regular expression being introduced. I had been introduced to regular expressions on Stack Overflow where I was trying to recognize if some text measurement put in by a user was in a valid form or not. For instance, the imperial system of measurement where you have feet and inches can be represented in so many different ways. I had eventually turned to regular expressions as an easy way to check if my parser could correctly parse the text or not and convert it to a normalize measurement. So some rules about languages and regular expressions… Any finite language can be represented by at least one if not more regular expressions A regular expressions is almost a rule syntax for expressing how regular languages can be formed regular expressions are cool For a regular expression to be valid for a language it must be able to generate all the words in the language and no other words. This is important. It doesn’t help me if my regular expression parses 100% of my measurement texts but also lets one or two invalid texts to pass as well. Okay, so this posting jumps around a bit – but introduces some very basic fundamentals for the subject which will be built on in later postings… Time to go and do some practical examples now…

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  • O'Reilly deal of the week to 23:59 PT 4/Sept/2012 - Master Regular Expressions

    - by TATWORTH
    O'Reilly at http://shop.oreilly.com/category/deals/regular-expressions-owo.do?code=WKRGEX are offering 50% off a range of e-books on mastering Regular Expressions "Take the guesswork out of using regular expressions. Learn powerful tips for matching, extracting, and transforming text as well as the gotchas to avoid. For one week only, SAVE 50% on these e-books and discover a whole new world of mastery over your code." I recommend Mastering Regular Expression to Dot Net developer as it covers the use of regular expressions across a number of environments, including Dot Net.

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