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• Regular expression for Regular expressions?

  - by kavoir.com

  I have an app that enables the user to input a regular expression, my question is how to check against any input of regular expressions and make sure they are valid ones because if they are not there will be preg_match errors. I don't want to use the '@' before preg_match, so if there's a way to check the validity of the user input of regular expressions that'd be great. The regular expression system of PHP seems to be rather too complicated for me to come up with a regular expression for them. Any idea or any alternatives would be possible in achieving this?

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• Regular expression in Umbraco for number validation.

  - by Vizioz Limited

  This evening I was looking for a way to validate an Umbraco node that could be either text or a numeric value, in my case a salary that could be either an hourly amount, an annual figure or a comment. In the case where the node contained a value I wanted the XSLT to output a pound sign (£) and for any that contained text it would just output the text, as this could be something like "Contact Us" or "Negotiable"I thought someone else might find this useful so here is the XSLT and the regular expression.First if you are using Umbraco, don't forget to include the reference to the EXSLT Regular expression library at the top of your XSLT.<xsl:stylesheet version="1.0" xmlns:xsl="http://www.w3.org/1999/XSL/Transform" xmlns:msxml="urn:schemas-microsoft-com:xslt" xmlns:umbraco.library="urn:umbraco.library" xmlns:Exslt.ExsltRegularExpressions="urn:Exslt.ExsltRegularExpressions" exclude-result-prefixes="msxml umbraco.library Exslt.ExsltRegularExpressions">Then the code I used was:<xsl:if test="Exslt.ExsltRegularExpressions:match($currentPage/data [@alias='Salary'], '^[0-9]*\,?[0-9]*\.?[0-9]+$') != ''"> <xsl:text>£</xsl:text></xsl:if>This regular expression allows any number of digits, an optional comma, more digits, an optional decimal point and finally more digits, so all the following are valid:12,00014.43334,342.03

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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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• deriving regular expressions from a regular language

  - by kayn

  Given the language below, how do i find a regular expression for the language L = {a ^n b ^m | n = 1, m =1, nm =3}

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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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• Regular Expression HTML tags

  - by user134615

  I'd like to know whether it exists a way to put the following HTML tags in a regex. What I want is a regex that can match all the start tags with their corresponding closing tags. E.g., Hello There might be more tags inside. I had thought of something like this: ^<([a-z]+)([^<]+)(?:(.)</\1|\s+/)$/, but it wont work. Sorry if this question doesnt belong to this section. Thank you.

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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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• Documentation often ommits to specify which flavour of regular expression to use, so is there a default flavour that we should all be familiar with?

  - by JW01

  Often I come across documentation that says "use a regular expression here" I have to spend quite some time digging around trying to work out which regular expression format they are expecting. As far as I can tell, there are many types of regular expression. But, at my last place of work I was made to feel stupid when I suggested adding some text to our User Documentation to specify the type of regular expression to be used. When someone says "a regular expression" what is the regular expression syntax most people expect and where is it documented? Update: I was prompted to single-out some examples - but no disrespect to these great projects: eregi docs page is not particularly helpful in explaining expected syntax. Nor can I easily work out the syntax expected here if i just land on the page from a search. No explicit mention of the regular expression pattern expected by PatternExpectation() on the SimpleTest page. etc. etc. here is a highly voted SO answer that seems to assume there is only one flavour of regular expressions.

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• Regular expression help

  - by DJPB

  I there I'm working on a C# app, and I get a string with a date or part of a date and i need to take day, month and year for that string ex: string example='31-12-2010' string day = Regex.Match(example, "REGULAR EXPRESSION FOR DAY").ToString(); string month = Regex.Match(example, "REGULAR EXPRESSION FOR MONTH").ToString() string year = Regex.Match(example, "REGULAR EXPRESSION FOR YEAR").ToString() day = "31" month = "12" year = "2010" ex2: string example='12-2010' string month = Regex.Match(example, "REGULAR EXPRESSION FOR MONTH").ToString() string year = Regex.Match(example, "REGULAR EXPRESSION FOR YEAR").ToString() month = "12" year = "2010" any idea? tks

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• What's a regular language?

  - by Javier Badia

  I've read that you can't parse HTML with regular expressions because HTML is not a regular language. I tried searching Wikipedia, but I didn't understand a word of what the various related articles said. Can someone explain, in simpler terms, what's a regular (or non-regular) language, and why non-regular languages can't be parsed with regexes?

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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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• Watchguard Firewall WebBlocker Regular Expression for Multiple Domains?

  - by Eric

  I'm pretty sure this is really a regex question, so you can skip to REGEX QUESTION if you want to skip the background. Our primary firewall is a Watchguard X750e running Fireware XTM v11.2. We're using webblocker to block most of the categories, and I'm allowing needed sites as they arise. Some sites are simple to add as exceptions, like Pandora radio. That one is just a pattern matched exception with "padnora.com/" as the pattern. All traffic from anywhere on pandora.com is allowed. I'm running into trouble on more sophisticated domains that reference content off of their base domains. We'll take GrooveShark as a sample. If you go to http://grooveshark.com/ and view page source, you'll see hrefs referring to gs-cdn.net as well as grooveshar.com. So adding a WebBlocker exception to grooveshark.com/ is not effective, and I have to add a second rule allowing gs-cdn.net/ as well. I see that the WebBlocker allows regex rules, so what I'd like to do in situations like this is create a single regex rule that allows traffic to all the needed domains. REGEX QUESTION: I'd like to try a regex that matches grooveshark.com/ and gs-cdn.net/. If anybody can help me write that regex, I'd appreciate it. Here is what is in the WatchGuard documentation from that section: Regular expression Regular expression matches use a Perl-compatible regular expression to make a match. For example, .[onc][eor][gtm] matches .org, .net, .com, or any other three-letter combination of one letter from each bracket, in order. Be sure to drop the leading “http://” Supports wild cards used in shell script. For example, the expression “(www)?.watchguard.[com|org|net]” will match URL paths including www.watchguard.com, www.watchguard.net, and www.watchguard.org. Thanks all!

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• nginx dynamic servername with regular expression doesn't work for co.uk

  - by redn0x

  I'm trying to setup a nginx server which dynamically loads content from a folder for a domain. To do this I'm using regular expressions in the server name like so: server_name ((?<subdomain>.+)\.)?(?<domain>.+)\.(?<tld>.*); This will create a 3 variables for nginx to use later on, for example when using the following url: test.foo.example.com this will evaluate to: $subdomain = test.foo $domain = example $tld = com The problem arises when the co.uk top-level domain is used. In this case when using the url test.foo.example.co.ukit will evaluate to: $subdomain = test.foo.cedira $domain = co $tld = uk How can I edit the regular expression so that it will also work for co.uk?

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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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• 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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• generalizing the pumping lemma for UNIX-style regular expressions

  - by Avi

  Most UNIX regular expressions have, besides the usual *,+,? operators a backslash operator where \1,\2,... match whatever's in the last parentheses, so for example L=(a)b\1* matches the (non regular) language a^n b a^n On one hand, this seems to be pretty powerful since you can create (a*)b\1b\1 to match the language a^n b a^n b a^n which can't even be recognized by a stack automaton. On the other hand, I'm pretty sure a^n b^n cannot be expressed this way. Two questions: 1. Is there any literature on this family of languages (UNIX-y regular). In particular, is there a version of the pumping lemma for these? 2. Can someone prove (or perhaps disprove) that a^n b^n cannot be expressed this way? Thanks

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• Regular expressions question?

  - by php

  are regular expressions the same for PHP, mysql, javascript, pearl and so on and if so is there a chart or tutorial that explains regular expressions?

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• C# Regular Expression to find multiple sequences of punctuation characters

  - by Aran Mulholland

  Im trying to match punctuations using regular expressions. Do i have to specify every punctuation character i am searching for or is there is an escape sequence i can use? Im sitting here smiling to myself that the answers i might get will just be "Yes" or "No", please elaborate.... (that sentence should match the regular expression twice)

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• Make regular expression case insensitive

  - by Jeremy

  Given this regular expression: "^[0-9]\s(lbs|kg|kgs)$" how do I make it case insensitive? I am trying to use this in a .net regular expression validator, so I need to specify case insensitivity in the pattern.

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• Remove duplicate characters using a regular expression

  - by Alex

  I need to Match the second and subsequent occurances of the * character using a regular expression. I'm actually using the Replace method to remove them so here's some examples of before and after: test* -> test* (no change) *test* -> *test test** *e -> test* e Is it possible to do this with a regular expression? Thanks

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• Regular Expressions, Checking for a range of occurrences

  - by gmcalab

  I have a phone number I want to match against a regular expression. The format of the phone number must match this: (123) 123-4567 x12345 The extension is optional. Also the extension must contain 1-5 numbers. Below is a regular expression I wrote that works. ^\(\d{3}\) \d{3}-\d{4}( x\d\d?\d?\d?\d?)?$ I was wondering if there is a better way to check for the extension instead of x\d\d?\d?\d?\d? Can I say 1-5 occurrences of \d instead of the above some how ?

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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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• The Definition of Regular Languages

  - by AraK

  Good Day, I have tried, and burned my brain to understand the definition of Regular Languages in Discrete Mathematics and its Applications(Rosen) without reaching the goal of understanding why the definition is like that in this book. On page(789), I am rephrasing the definition: Type 3 grammars are defined as: w1 --> w2 Where w1 is a non-terminal, and w2 is of the form: w2 = aB w2 = a Where B is a non-terminal, and a is a terminal. A special case is when w1 is the starting symbol and w2 is lambda(the empty string): w1 = S S --> lambda Two questions I couldn't find an answer for. First, Why can't w2 be of the form Ba. Second, Why lambda is only allowed for the starting symbol only. The book states that, regular languages are equivalent to Finite State Automaton, and we can easily see that a we can build FSA for both cases. I took a look at other resources, and these restrictions don't exist in these resources. Thanks,

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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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