I find that the problem is much more general than I assumed. Most or all switches are incompatible with the --gui switch. Even worse than the ability to give -P switches is the inability to specify a build file name. At least with -P, graphical users could click to open an editor with their properties file, but the GUI is useless for non-graphical users who want to do builds with a build file that happens to not be named "gradle.build". No UI entry to set or change the build file. No command-line switch.

As announced on the Gradle blog we are planning to completely migrate issues from JIRA to GitHub.

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My original description seems to still be accurate. Can be verified easily by running say:

gradlew --gui -b tst.gradle

and seeing that the -b switch is ignored.

The Gradle GUI has been deprecated and is scheduled to be removed with Gradle 4.0. We are not going to work on this issue anymore.