[MPH-192] need <skip> option for evaluate goal

**[Garret Wilson](https://issues.apache.org/jira/secure/ViewProfile.jspa?name=garretwilson)** opened **[MPH-192](https://issues.apache.org/jira/browse/MPH-192?redirect=false)** and commented

It is typical and even expected for Maven plugins to have a `` option, so that we can provide (via properties, profiles, etc.) a way to skip the plugin execution. See for example the [Antrun Plugin `` option](https://maven.apache.org/plugins/maven-antrun-plugin/run-mojo.html#skip) and the [Maven Assembly Plugin `` option](https://maven.apache.org/plugins/maven-assembly-plugin/single-mojo.html#skipAssembly). (I could provide a long list of similar plugins.)

Please provide a Maven configuration option to skip execution for the `evaluate` goal.

This is particularly important because the Maven Help Plugin provides the only means to generate output to a file which is recognized across many development environments. (For example, Antrun `` can generate a file, but it is not supported by Eclipse.)

It is important to be able to able to configure in the POM to evaluate an expression and output to a file _only_ under certain conditions. Currently the lack of this functionality is blocking my use of the Maven Help Plugin `evaluate` goal and I am forced to look for other options, or limp along with Antrun not working in Eclipse.

Thank you.

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**Affects:** 3.3.0

Start at the Maven Help Plugin implementation for the evaluate goal and inspect how its parameters are declared and tested. Compare skip options in the referenced Maven plugins, then verify that a POM-configured skip prevents evaluation while existing evaluation and file-output behavior remains unchanged.

Written by the indexing model from the issue text.