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May 13, 2015 – Tony Borres Regex - Replace with Groups

I was recently confronted with a situation that required me to search and replace my code in a way that the left and right of my search needed to be replaced, but the middle needed to remain the same. Could this be done with a single search and replace?

The Problem

For reasons that I do not care to detail here, I found myself needing to replace every instance of my Visual Studio solution where a template line matching

template: require('Project/DynamicComponentName/DynamicComponentName.html')

is replaced with a templateUrl

templateUrl: 'Project/DynamicComponentName/DynamicComponentName.html'

In this example the DynamicComponentName is different in every instance.

Rather than manually identifying every template line and make the necessary changes I wanted to do a single search and replace and be done with it. Regex felt like the right answer, but how?

Regex Groups

Regex, or regular expressions, is a very powerful (read as: “complicated to use and understand”) pattern matching grammar. It provides for more advanced searching capabilities than a standard text-base search. Luckily Visual Studio provides for searching via Regex (screenshot is of Visual Studio 2013).

Visual Studio regex search option

With Use Regular Expressions selected in Visual Studio we can take advantage of regex, including its group capturing via parentheses.

In the Find what we can place the following regex query

template: require\('Project/(.*)'\)

This tells Visual Studio to match everything that directly matches template: require(Project/<any number of characters>)'. Note that the require’s parentheses needed to be escaped with \ because the parentheses are part of the regex syntax. You can use the online tool to test the regex matcher on your own.

Now if we place the following in the Replace with field we’ll be able to place the contents captured by the (.*) capture group using the $ syntax.

templateUrl: 'Project$1'

The contents of the capture group will be placed in the $1 slot. If you had more than one capture group then you would simply increment the $ ($1, $2, etc) based on the order that the capture groups appeared in the search term.

Now hit Replace for each instance and you’re good to go.

In my situation I really wanted to use Replace All, but Visual Studio 2013 seems to have an issue with Replace All using regex. Using Replace All results in Visual Studio stating that it cannot find any matches. Silly Visual Studio.

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