How to pass parameters or arguments into a Gradle task?

I have a Gradle build script into which I am trying to include Eric Wendelin's CSS plugin.

It's easy enough to implement, and because I only want minification (rather than combining and gzipping), I've got the pertinent parts of the build script looking like this:

minifyCss {
    source = "src/main/webapp/css/brandA/styles.css"
    dest = "${buildDir}/brandA/styles.css"
    yuicompressor {
        lineBreakPos = -1
    }
}

war {
    baseName = 'ex-ren'
}

war.doFirst {
    tasks.myTask.minifyCss.execute()
}

This is perfect - when I run the gradle war task, it calls the minifyCss task, takes the source css file, and creates a minified version in the buildDir

However, I have a handful of css files which need minify-ing, but not combining into one file (hence I'm not using the combineCss task)

What I'd like to be able to do is make the source and dest properties (assuming that's the correct terminology?) of the minifyCss task reference variables of some sort - either variables passed into the task in the signature, or global variables, or something ...

Something like this I guess (which doesn't work):

minifyCss(sourceFile, destFile) {
    source = sourceFile
    dest = destFile
    yuicompressor {
        lineBreakPos = -1
    }
}

war {
    baseName = 'ex-ren'
}

war.doFirst {
    tasks.myTask.minifyCss.execute("src/main/webapp/css/brandA/styles.css", "${buildDir}/brandA/styles.css")
    tasks.myTask.minifyCss.execute("src/main/webapp/css/brandB/styles.css", "${buildDir}/brandB/styles.css")
    tasks.myTask.minifyCss.execute("src/main/webapp/css/brandC/styles.css", "${buildDir}/brandC/styles.css")
}

This doesn't work either:

def sourceFile = null
def destFile = null

minifyCss {
    source = sourceFile
    dest = destFile
    yuicompressor {
        lineBreakPos = -1
    }
}

war {
    baseName = 'ex-ren'
}

war.doFirst {
    sourceFile = "src/main/webapp/css/brandA/styles.css"
    destFile = "${buildDir}/brandA/styles.css"
    tasks.myTask.minifyCss.execute()
}

For the life of me I cannot work out how to call a task and pass variables in :(

Any help very much appreciated;

You should consider passing the -P argument in invoking Gradle.

From Gradle Documentation :

> --project-prop Sets a project property of the root project, for example -Pmyprop=myvalue. See Section 14.2, “Gradle properties and system properties”.

Considering this build.gradle

task printProp << {
    println customProp
}

Invoking Gradle -PcustomProp=myProp will give this output :

$ gradle -PcustomProp=myProp printProp
:printProp
myProp

BUILD SUCCESSFUL

Total time: 3.722 secs

This is the way I found to pass parameters.

If the task you want to pass parameters to is of type JavaExec and you are using Gradle 5, for example the application plugin's run task, then you can pass your parameters through the --args=... command line option. For example gradle run --args="foo --bar=true".

Otherwise there is no convenient builtin way to do this, but there are 3 workarounds.

1. If few values, task creation function

If the possible values are few and are known in advance, you can programmatically create a task for each of them:

void createTask(String platform) {
   String taskName = "myTask_" + platform;
   task (taskName) {
      ... do what you want
   }
}

String[] platforms = ["macosx", "linux32", "linux64"];
for(String platform : platforms) {
    createTask(platform);
}

You would then call your tasks the following way:

./gradlew myTask_macosx

2. Standard input hack

A convenient hack is to pass the arguments through standard input, and have your task read from it:

./gradlew myTask <<<"arg1 arg2 arg\ in\ several\ parts"

with code below:

String[] splitIntoTokens(String commandLine) {
	String regex = "(([\"']).*?\\2|(?:[^\\\\ ]+\\\\\\s+)+[^\\\\ ]+|\\S+)";
	Matcher matcher = Pattern.compile(regex).matcher(commandLine);
	ArrayList<String> result = new ArrayList<>();
	while (matcher.find()) {
	    result.add(matcher.group());
	}
	return result.toArray();   
}

task taskName, {
		doFirst {
			String typed = new Scanner(System.in).nextLine();
			String[] parsed = splitIntoTokens(typed);
			println ("Arguments received: " + parsed.join(" "))
			... do what you want
		} 
 }

You will also need to add the following lines at the top of your build script:

import java.util.regex.Matcher;
import java.util.regex.Pattern;
import java.util.Scanner;

3. -P parameters

The last option is to pass a -P parameter to Gradle:

./gradlew myTask -PmyArg=hello

You can then access it as myArg in your build script:

task myTask {
    doFirst {
       println myArg
       ... do what you want
    }
}

Credit to @789 for his answer on splitting arguments into tokens

I would suggest the method presented on the Gradle forum:

def createMinifyCssTask(def brand, def sourceFile, def destFile) {
    return tasks.create("minify${brand}Css", com.eriwen.gradle.css.tasks.MinifyCssTask) {
        source = sourceFile
        dest = destFile
    }
}

I have used this method myself to create custom tasks, and it works very well.

task mathOnProperties << {
	println Integer.parseInt(a)+Integer.parseInt(b)
	println new Integer(a) * new Integer(b)
}

---

$ gradle -Pa=3 -Pb=4 mathOnProperties
:mathOnProperties
7
12

BUILD SUCCESSFUL

Its nothing more easy.

run command: ./gradlew clean -PjobId=9999

and

in gradle use: println(project.gradle.startParameter.projectProperties)

You will get clue.

I think you probably want to view the minification of each set of css as a separate task

task minifyBrandACss(type: com.eriwen.gradle.css.tasks.MinifyCssTask) {
     source = "src/main/webapp/css/brandA/styles.css"
     dest = "${buildDir}/brandA/styles.css"
}

etc etc

BTW executing your minify tasks in an action of the war task seems odd to me - wouldn't it make more sense to make them a dependency of the war task?

Here is a solution for Kotlin DSL (build.gradle.kts).

I first try to get the variable as a property and if it was null try to get it from OS environment variables (can be useful in CIs like GitHub Actions).

tasks.create("MyCustomTask") {
    val songName = properties["songName"]
        ?: System.getenv("SONG_NAME")
        ?: error("""Property "songName" or environment variable "SONG_NAME" not found""")

    // OR getting the property with 'by'. Did not work for me!
    // For this approach, name of the variable should be the same as the property name
    // val songName: String? by properties

    println("The song name: $songName")
}

We can then pass a value for the property from command line:

./gradlew MyCustomTask -PsongName="Black Forest"

Or create a file named local.properties at the root of the project and set the property:

songName=Black Forest

We can also add an env variable named SONG_NAME with our desired value and then run the task:

./gradlew MyCustomTask