.gitignore

/.gradle/
/build/
/buildSrc/
generated.conf

build.gradle

defaultTasks 'clean', 'generateConfig'

ext {
    templatesDir = projectDir // config templates location
    configTokens = [
        db: [
            host: 'localhost',
            name: 'test',
            user: 'test',
            pass: ''
        ]
    ]
}

task generateConfig(type: GenerateTemplate) {
    template = 'template.conf'
    target = file('generated.conf')
    expand configTokens // filter() can be used instead to replace tokens
}

task clean(type: Delete) {
    delete generateConfig.target
}

GenerateTemplate.groovy

/**
 * Move this class to buildSrc/src/main/groovy under your project.
 */

import org.gradle.api.tasks.Copy
import org.gradle.api.tasks.Input
import org.gradle.api.tasks.OutputFile
import org.gradle.api.tasks.Optional

import org.apache.tools.ant.filters.ReplaceTokens

class GenerateTemplate extends Copy {

    public final static BEGIN_TOKEN = '{'
    public final static END_TOKEN = '}'

    private String template
    private File target

    @Optional
    private Map<String, ?> properties

    def GenerateTemplate() {
        from(project.templatesDir)
    }

    public GenerateTemplate setTemplate(String name) {
        this.template = name
        include(template)
        this
    }

    @Input
    public String getTemplate() {
        template
    }

    public GenerateTemplate setTarget(File file) {
        this.target = file
        into(target.getParent())
        this
    }

    @OutputFile
    public File getTarget() {
        target
    }

    @Override
    protected void configureRootSpec() {
        super.configureRootSpec()
        rename(template, target.getName())
    }

    /**
     * Configures a filter to replace tokens in a template.
     * The method should be called from configureRootSpec().
     */
    private GenerateTemplate configureFilter() {
        filter(ReplaceTokens, tokens: properties, beginToken: BEGIN_TOKEN, endToken: END_TOKEN)
        this
    }

}

template.conf

db.host = ${db.host}
db.name = ${db.name}
db.user = ${db.user}
db.pass = ${db.pass}