How to define and call custom methods in build.gradle

One approach given below:

ext.myMethod = { param1, param2 ->
    // Method body here
}

Note that this gets created for the project scope, ie. globally available for the project, which can be invoked as follows anywhere in the build script using myMethod(p1, p2) which is equivalent to project.myMethod(p1, p2)

The method can be defined under different scopes as well, such as within tasks:

task myTask {
    ext.myMethod = { param1, param2 ->
        // Method body here
    }

    doLast {
        myMethod(p1, p2) // This will resolve 'myMethod' defined in task
    }
}

If you have defined any methods in any other file *.gradle - ext.method() makes it accessible project wide. For example here is a

versioning.gradle

// ext makes method callable project wide
ext.getVersionName = { ->
    try {
        def branchout = new ByteArrayOutputStream()
        exec {
            commandLine 'git', 'rev-parse', '--abbrev-ref', 'HEAD'
            standardOutput = branchout
        }
        def branch = branchout.toString().trim()

        if (branch.equals("master")) {
            def stdout = new ByteArrayOutputStream()
            exec {
                commandLine 'git', 'describe', '--tags'
                standardOutput = stdout
            }
            return stdout.toString().trim()
        } else {
            return branch;
        }
    }
    catch (ignored) {
        return null;
    }
}

build.gradle

task showVersion << {
    // Use inherited method
    println 'VersionName: ' + getVersionName()
}

Without ext.method() format , the method will only be available within the *.gradle file it is declared. This is the same with properties.