Obtain a git hash in gradle, using JGit. Useful in environments where people frown on just putting a shell exec in your gradle file like so: "git log -1 --pretty=%H".execute().

build.gradle

// In buildSrc/

apply plugin: 'groovy'

repositories {
    jcenter()
    maven { url "https://plugins.gradle.org/m2/" }
}

dependencies {
    compile gradleApi()
    compile localGroovy()
    compile 'org.eclipse.jgit:org.eclipse.jgit:4.1.1.201511131810-r'
}

GitFunctions.groovy

// In buildSrc/src/main/groovy/

import org.eclipse.jgit.api.Git
import org.eclipse.jgit.lib.RepositoryBuilder
import org.gradle.api.Project

class GitFunctions {

    public static String headCommitAndStatus(Project project) {
        def repo = new RepositoryBuilder()
                .setGitDir(new File(project.rootDir, '/.git'))
                .readEnvironment()
                .build()

        def version = repo.getRef('HEAD').getObjectId().name
        def isClean = Git.wrap(repo).status().call().isClean()
        return version + (isClean ? '' : '.dirty')
    }
}

To invoke this in your build.gradle: "${GitFunctions.headCommitAndStatus(project)}".