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MSBuild conditions

  • Artikkeli

MSBuild supports a specific set of conditions that can be applied wherever a Condition attribute is allowed. The following table explains those conditions.

Condition Description
'stringA' == 'stringB' Evaluates to true if stringA equals stringB.

For example:

Condition="'$(Configuration)'=='DEBUG'"

Single quotes are not required for simple alphanumeric strings or boolean values. However, single quotes are required for empty values. This check is case insensitive.
'stringA' != 'stringB' Evaluates to true if stringA is not equal to stringB.

For example:

Condition="'$(Configuration)'!='DEBUG'"

Single quotes are not required for simple alphanumeric strings or boolean values. However, single quotes are required for empty values. This check is case insensitive.
<, >, <=, >= Evaluates the numeric values of the operands. Returns true if the relational evaluation is true. Operands must evaluate to a decimal or hexadecimal number or a four-part dotted version. Hexadecimal numbers must begin with "0x". Note: In XML, the characters < and > must be escaped. The symbol < is represented as &lt;. The symbol > is represented as &gt;.
Exists('stringA') Evaluates to true if a file or folder with the name stringA exists.

For example:

Condition="!Exists('$(Folder)')"

Single quotes are not required for simple alphanumeric strings or boolean values. However, single quotes are required for empty values.
HasTrailingSlash('stringA') Evaluates to true if the specified string contains either a trailing backward slash (\) or forward slash (/) character.

For example:

Condition="!HasTrailingSlash('$(OutputPath)')"

Single quotes are not required for simple alphanumeric strings or boolean values. However, single quotes are required for empty values.
! Evaluates to true if the operand evaluates to false.
And Evaluates to true if both operands evaluate to true.
Or Evaluates to true if at least one of the operands evaluates to true.
() Grouping mechanism that evaluates to true if expressions contained inside evaluate to true.
$if$ ( %expression% ), $else$, $endif$ Checks whether the specified %expression% matches the string value of the passed custom template parameter. If the $if$ condition evaluates to true, then its statements are run; otherwise, the $else$ condition is checked. If the $else$ condition is true, then its statements are run; otherwise, the $endif$ condition ends expression evaluation.

For examples of usage, see Visual Studio project/item template parameter logic.

You can use string methods in conditions, as shown in the following example, in which the TrimEnd() function is used to compare only the relevant part of the string, to differentiate between .NET Framework and .NET Core target frameworks.

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

    <PropertyGroup>
        <TargetFrameworks>net45;net48;netstandard2.1;netcoreapp2.1;netcoreapp3.1</TargetFrameworks>
    </PropertyGroup>

    <PropertyGroup Condition="'$(TargetFramework.TrimEnd(`0123456789`))' == 'net'">
        <!-- Properties for .NET Framework -->
    </PropertyGroup>

</Project>

In MSBuild project files, there's no true Boolean type. Boolean data is represented in properties that might be empty or set to any value. Therefore, '$(Prop)' == 'true' means "if Prop is true," but '$(Prop)' != 'false' means "if Prop is true or unset or set to something else."

Boolean logic is only evaluated in the context of conditions, so property settings such as <Prop2>'$(Prop1)' == 'true'</Prop> are represented as a string (after variable expansion), not evaluated as Boolean values.

MSBuild implements a few special processing rules to make it easier to work with string properties that are used as Boolean values. Boolean literals are accepted, so Condition="true" and Condition="false" work as expected. MSBuild also includes special rules to support the Boolean negation operator. So, if $(Prop) is 'true', !$(Prop) expands to !true and this compares equal to false, as you would expect.

Comparing versions

The relational operators <, >, <=, and >= support versions as parsed by System.Version, so you can compare versions that have four numeric parts to each other. For instance '1.2.3.4' < '1.10.0.0' is true.

Caution

System.Version comparisons can produce surprising results when one or both versions do not specify all four parts. For instance, version 1.1 is older than version 1.1.0.

MSBuild provides property functions to compare versions that have a different set of rules compatible with semantic versioning (semver).

See also