This is no longer required... you can now inject C# into the project/build file...

Define a custom task and parameters as follows:

<UsingTask TaskName="ReplaceFileText" TaskFactory="CodeTaskFactory" AssemblyFile="$(MSBuildToolsPath)\Microsoft.Build.Tasks.v4.0.dll">
  <ParameterGroup>
    <InputFilename ParameterType="System.String" Required="true" />
    <OutputFilename ParameterType="System.String" Required="true" />
    <MatchExpression ParameterType="System.String" Required="true" />
    <ReplacementText ParameterType="System.String" Required="true" />
  </ParameterGroup>
  <Task>
    <Reference Include="System.Core" />
    <Using Namespace="System" />
    <Using Namespace="System.IO" />
    <Using Namespace="System.Text.RegularExpressions" />
    <Code Type="Fragment" Language="cs">
      <![CDATA[
            File.WriteAllText(
                OutputFilename,
                Regex.Replace(File.ReadAllText(InputFilename), MatchExpression, ReplacementText)
                );
          ]]>
    </Code>
  </Task>
</UsingTask>

Then simply call it like any other MSBuild task

<Target Name="AfterBuild">
  <ReplaceFileText 
    InputFilename="$(OutputPath)File.exe.config" 
    OutputFilename="$(OutputPath)File.exe.config" 
    MatchExpression="\$version\$" 
    ReplacementText="1.0.0.2" />
</Target>

The above example replaces "$version$" with "1.0.0.2" in the "File.exe.config" located in the output directory.


There is very simple approach to just replace string in a file:

  <Target Name="Replace" AfterTargets="CoreCompile">
      <PropertyGroup>
          <InputFile>c:\input.txt</InputFile>
          <OutputFile>c:\output.txt</OutputFile>
      </PropertyGroup>
      <WriteLinesToFile
          File="$(OutputFile)"
          Lines="$([System.IO.File]::ReadAllText($(InputFile)).Replace('from','to'))"
          Overwrite="true"
          Encoding="Unicode"/>
  </Target>

See https://docs.microsoft.com/en-us/visualstudio/msbuild/property-functions?view=vs-2019 to explore inlinable C# code. [System.Text.RegularExpressions.Regex] included into the list.


The answer from @csharptest.net is good, but it doesn't work on DotNetCore. I would have added this as a comment, but I don't have enough reputation.

On DotNetCore you have to update:

  • Task Factory to "RoslynCodeTaskFactory"
  • Task Assembly to "$(MSBuildToolsPath)\Microsoft.Build.Tasks.Core.dll"
  • Remove the reference to "System.Core"
  • The consuming Target has to specify the "AfterTargets" attribute as "Build"

Everything else should be the same:

<Project Sdk="Microsoft.NET.Sdk.Web">
  ...

  <UsingTask
    TaskName="ReplaceFileText"
    TaskFactory="RoslynCodeTaskFactory"
    AssemblyFile="$(MSBuildToolsPath)\Microsoft.Build.Tasks.Core.dll">
    <ParameterGroup>
      <InputFilename ParameterType="System.String" Required="true" />
      <OutputFilename ParameterType="System.String" Required="true" />
      <MatchExpression ParameterType="System.String" Required="true" />
      <ReplacementText ParameterType="System.String" Required="true" />
    </ParameterGroup>
    <Task>
      <Using Namespace="System"/>
      <Using Namespace="System.IO"/>
      <Using Namespace="System.Text.RegularExpressions" />
      <Code Type="Fragment" Language="cs">
        <![CDATA[  
          File.WriteAllText(
            OutputFilename,
            Regex.Replace(File.ReadAllText(InputFilename), MatchExpression, ReplacementText)
            );
        ]]>
      </Code>
    </Task>
  </UsingTask>

  <Target Name="AfterBuildStep" AfterTargets="Build">
    <ReplaceFileText
       InputFilename="$(OutputPath)File.exe.config" 
       OutputFilename="$(OutputPath)File.exe.config" 
       MatchExpression="\$version\$" 
       ReplacementText="1.0.0.2" />
  </Target>
</Project>

EDIT: This answer is obsolete. Use solution below...

Use ReadLinesFromFile task to get replacement string from the xy.xml file. Check this

Then use value from xy.xml as a replacement string for FileUpdate task. Check this

And put it all together ;)


You can use the task FileUpdate from MSBuild Community Tasks as explained in the article http://geekswithblogs.net/mnf/archive/2009/07/03/msbuild-task-to-replace-content-in-text-files.aspx