Therefore, the pattern rules that apply to reFind() and reReplace() (POSIX) are not necessarily the same as the pattern rules that apply to instances of the Java class,. To break down what is happening, here's the type of notation that you can use in the two phases of ColdFusion regular expression pattern execution:ĬoldFusion is built on top of Java but, Java uses a different regular expression engine. This is a nice string because it is composed of a repeated pattern, "ha." When we run the above code, we get the following output: In the following script, I am going to use both functions to test the various back-reference approaches in the two phases of pattern execution:Īs you can see here, we are using the string, "ha ha" in all cases. In ColdFusion, we can use the reFind() and reReplace() functions to find and replace regular expressions respectively. replacing) and is what I will be exploring below. Which notation you use - \N or $N - depends both on the technology and the execution phase (matching vs. In either case, the "N" is the numerical digit, 1-9, that represents the index of the captured group. These groups can be referenced using back-references - \N and $N - both when matching and replacing a given pattern. You would get the following captured groups: So, for example, in the following regular expression pattern: There are some exceptions to this, and you can use a syntax that performs non-captured grouping but, for the most part, groups are captured from left-to-right by parenthesis.
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In a regular expression, most anything wrapped in parenthesis is known a captured group. As such, I thought I would write up a quick comparison of the regular expression back-references for the three main languages that I use: ColdFusion, Java, and Javascript. But, this does happen to be one of those things that is a bit different in each technology. It can only be one or the other, so figuring it out is generally not a big issue. Use the methods of the System.The other day, I was talking to Ryan Jeffords about regular expressions (RegEx) and there was some confusion about when to use \N versus when to use $N as a captured-group back-reference. For example, the String.Contains, String.EndsWith, and String.StartsWith methods determine whether a string instance contains a specified substring and the String.IndexOf, String.IndexOfAny, String.LastIndexOf, and String.LastIndexOfAny methods return the starting position of a specified substring in a string. The System.String class includes several search and comparison methods that you can use to perform pattern matching with text.
#When does regular expression not work download#
There are also a number of online libraries of regular expression patterns, such as the one at .įor more information about using the Regex class, see the following sections in this topic:įor more information about the regular expression language, see Regular Expression Language - Quick Reference or download and print one of these brochures: It can be used to quickly parse large amounts of text to find specific character patterns to extract, edit, replace, or delete text substrings and to add the extracted strings to a collection to generate a report.įor some common regular expression patterns, see Regular Expression Examples. NET Framework's regular expression engine. To prevent any misinterpretation, the example passes each dynamically generated string to the Escape method. ' The example displays the following output:īecause the regular expression in this example is built dynamically, we do not know at design time whether the current culture's currency symbol, decimal sign, or positive and negative signs might be misinterpreted by the regular expression engine as regular expression language operators.
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MatchCollection^ matches = rx->Matches( text ) Ĭonsole::WriteLine( " is not a currency value.", test) String^ text = "The the quick brown fox fox jumps over the lazy dog dog." Regex^ rx = gcnew Regex( "\\b(?\\w+)\\s+(\\k)\\b",static_cast(RegexOptions::Compiled | RegexOptions::IgnoreCase) ) Define a regular expression for repeated words. Using namespace System::Text::RegularExpressions Match the captured group that is named word. Match one or more white-space characters. Match one or more word characters up to a word boundary. The regular expression \b(?\w+)\s+(\k)\b can be interpreted as shown in the following table. The following example uses a regular expression to check for repeated occurrences of words in a string.