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Regular Expression Concatenation
Using Rule number 2 and Rule number 4, we can create regular expressions that consists of any sequence of symbols from our alphabet. Rule number 2 said that if the symbol a is in the alphabet, then a...
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Regular Expression Alternation
From rule number 2 and rule number 3 we can define paradigms — a number of possible patterns. This means that we add two or more languages by applying the set operator union to them. The union of the...
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The Kleene Star operator
All finite languages can be described by regular expressions. You can simply list the strings as an alternation string1|string2|string3 etc. But there are also some languages with an infinite number...
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Regular Expression Precedence
You might be tempted to read the following regular expression as third or fifth row: 'fifth row'.match /third|fifth row/ #=> #<MatchData "fifth row"> 'third row'.match /third|fifth row/...
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Simple Regular Expression Examples
Now, we have three operators and a small framework. After all this theory, you might wonder if it’s possible for us to solve any problems. Yes, of course we can. Here are some examples: All binary...
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From Regular Expression to Finite Automaton
For each regular expression — and I mean the three operators and the six recursive rules style — there is a finite automaton that accepts exactly the same strings. Since this is not a university book...
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The Scent of Regex Requisite
Did you know that the famous quote “Some people, when confronted with a problem, think: I know, I’ll use regular expressions. Now they have two problems.” dates all the way back to 1997? However, most...
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HTML5 Form Validation With Regex
Client side validation has always been a potential headache for front-end programmers. Embedded blocks with a mixture of imperative JavaScript and declarative regex can be a mess. HTML5 has ambition...
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Regular Expressions – a brief history
Regular Expressions is a programming language with which we can specify a set of strings. With the help of two operators and one function, we can be more concise than if we would have to list all the...
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Dot — The Regex Barbapapa
Remember Barbapapa — Annette Tison’s and Talus Taylor’s children’s books and films from the 1970s? The hero was a pink, pear-shaped guy with the ability to take on almost any shape whatsoever. The...
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