Purpose of << in gradle - gradle

I starting playing around gradle and trying to understand the purpose of <<.
On executing gradle -q task0 when build.gradle contains gave me task 0
4.times { counter ->
task "task$counter" <<{
println "task $counter"
}
}
where as executing gradle -q test{0123} when build.gradle contains
4.times { counter ->
task "task$counter" {
println "task $counter"
}
}
returning
task 0
task 1
task 2
task 3
Can someone help in understanding purpose of <<?

If you have << it will execute the print lines when the task is executed and not having it executes the print lines when the task is configured.
This can effect your output since the Gradle Lifecycle is Initialization > Configuration > Execution.
For example if your build.gradle contains:
task "task0" << {
println "task 0"
}
task "task1" {
println "task 1"
}
Then if you execute task0 you will get:
> gradlew -q task0
task 1
task 0
Even though you would only expect task 0 to print. While if you execute task1 you get:
> gradlew -q task1
task 1
This is because task1 is printing out during configuration which even though you are not running it, the whole build.gradle file gets read in during the configuration phase to determine what gets executed. You could even go:
> gradlew clean
task 1
And you get your output from task1.

I think the problem here is what << means. It is predefined shift left operator and with it we say to a Gradle task. "Gradle task, I want closure which is after << to be put as your last action".So with
task "taskHello" <<{
println "Hello Gradle action"
}
you say in my build I have a task, which name is taskHello and I want when excecute it with
gradle taskHello
To do action
{
println "Hello Gradle action"
}
<< is a syntax sugar short for doLast{}, so you can rewrite your task like this:
4.times { counter ->
task "task$counter" {
doLast{
println "task $counter"
}
}
}

Related

How to use commandLine() within buildFinished

In $HOME/.gradle/init.gradle I have:
gradle.buildFinished { buildResult ->
commandLine 'bash', "blah blah blah"
}
Doing gradle build the build succeeds, but after it succeeds I get the error:
Could not find method commandLine() for arguments [bash, blah blah blah] on build 'FooBar' of type org.gradle.invocation.DefaultGradle.
The answer to the question Could not find method commandLine() doesn't help as either putting (type: Exec) after gradle.buildFinished or wrapping the whole thing in exec { } causes Gradle to fail right from the start rather than the build succeeding and then my post-build hook failing.
I'm using Gradle version 6.3
You've misconfigured commandLine. With the following build.gradle:
task lol {
doLast {
println "lol"
}
}
and ~/.gradle/init.gradle:
gradle.buildFinished { buildResult ->
exec {
commandLine 'bash', '-c', 'echo lol2'
}
}
it works as expected.

dependsOn another task with a parameter value

I have a task from a plugin which I call on command line like this:
$ gradle myTask -PsomeArg=<value>
I want to define another task that would do exactly the same with a default parameter value. I expect to be able to call it like this:
$ gradle otherTask
I assume my task should look something like this:
task otherTask (dependsOn: 'myTask', someArg: 'value') {...}
You could define a task that would set default value for project property someArg when this value is not provided as command line parameter :
task otherTask (){
finalizedBy myTask
doFirst{
if (!project.hasProperty("someArg")) {
project.ext.set("someArg", "defaultValue")
}
}
}
Note that you need to use finalizedBy dependency type here: if you use otherTask.dependsOn myTask the task myTask will be executed first (so default value for property someArg will not be set yet)
Execution result:
./gradlew myTask -PsomeArg=myValue
> Task :myTask
executing task pluginTask with arg: myValue
./gradlew otherTask -PsomeArg=myValue
> Task :myTask
executing task pluginTask with arg: myValue
./gradlew otherTask
> Task :myTask
executing task pluginTask with arg: defaultValue

Gradle exec task fails with "execCommand == null!"

I have the following task in my build.gradle file:
task myTask(type:Exec) {
def stdout = new ByteArrayOutputStream()
exec {
commandLine 'cmd', '/c', 'whoami'
standardOutput = stdout;
}
println "Output: $stdout"
}
When I run my task with ./gradlew myTask, I get the following output:
> Configure project :
Output: retrovius
> Task :myTask FAILED
FAILURE: Build failed with an exception.
* What went wrong:
Execution failed for task ':myTask'.
> execCommand == null!
* Try:
Run with --stacktrace option to get the stack trace. Run with --info or --debug option to get more log output. Run with --scan to get full insights.
* Get more help at https://help.gradle.org
BUILD FAILED in 2s
1 actionable task: 1 executed
The task successfully outputs my username (retrovius), then fails anyway. Any pointers for what I'm doing wrong?
Depending on what you want to achieve, the answer you found is probably still not correct.
All tasks have two main stages: configuration and execution. Everything you put in the outermost block to the task definition is part of the configuration. And the exec method actually executes the command whenever that block of code is evaluated. So when you type:
task myTask() {
def stdout = new ByteArrayOutputStream()
exec {
commandLine 'cmd', '/c', 'whoami'
standardOutput = stdout;
}
println "Output: $stdout"
}
Then it means you are running the whoami command no matter what task you specify. If you run gradle -i help, it will print the name. I expect this is not what you intend.
Most of the time, you will want to run a command only when the task is actually executed. So if you want the command to only run if you type gradle -i myTask, you will need to do defer it to the execution stage instead. There are two ways you can do that.
Either you can put everything in a doLast block like this:
task myTask() {
doLast {
def stdout = new ByteArrayOutputStream()
exec {
commandLine 'cmd', '/c', 'whoami'
standardOutput = stdout
}
println "Output: $stdout"
}
}
Or you use the Exec type, like you already tried. The reason it didn't work for you is that you need to configure it with the command you like - and not actually run the command through the exec method. It could look like this:
task myTask(type: Exec) {
commandLine 'cmd', '/c', 'whoami'
standardOutput = new ByteArrayOutputStream()
doLast {
println "Output: $standardOutput"
}
}
You an also probably get rid of the cmd /c part. And println should only be used for debugging - use logger.info (or .warn, etc) if you need to output something to the user.
I figured out that the only thing I was doing wrong was to include the (type:Exec) in the definition of my task. If I place the following code in my build.gradle file:
task myTask() {
def stdout = new ByteArrayOutputStream()
exec {
commandLine 'cmd', '/c', 'whoami'
standardOutput = stdout;
}
println "Output: $stdout"
}
I get the following output:
> Configure project :
Output: retrovius
BUILD SUCCESSFUL in 2s
My mistake must have been that I was defining the task to be of type exec, but not giving it a command to run. This reveals a fundamental misunderstanding of the exec task and task type on my part. If anyone knows more specifically what I did wrong, please feel free to comment and explain or post a better answer.

Gradle. pass parameters to dependent project build script

I have project ("backend") configuration:
dependencies {
compile project(':model') //I would like to pass some params into this being build.
...
And other project ("frontend") configuration is very similar:
dependencies {
compile project(':model') //but from this project I will not pass params.
...
And when I build the dependant project model- I need to pass a parameter to it's build parameter and do something on condition. So for all projects who needs the sub-projects it will be built according to their needs.
To be more specific: When I build "backtend" - "model"'s project should run some task, but when I build "frontend" I don't.
Is it possible to force clean the sub-project as well?
You can easily pass parameters from command line, or by properties defined in gradle.properties or in ext. Here's a little project:
/build.gradle
ext {
var = "alpha"
}
task hello {
println "Name: $project.name"
println "Var: $var"
println "Param: $param"
println "Prop: $prop"
}
/gradle.properties
prop=gama
/settings.gradle
project.name = 'foo'
include 'bar'
/bar/build.gradle
task hello {
println "Name: $project.name"
println "Var: $var"
println "Param: $param"
println "Prop: $prop"
}
If you run gradle hello -Pparam=beta it will print:
Name: foo
Var: alpha
Param: beta
Prop: gama
Name: bar
Var: alpha
Param: beta
Prop: gama
:hello UP-TO-DATE
:bar:hello UP-TO-DATE

Isolated Gradle Tasks?

I'm trying to port over a somewhat convoluted Makefile to Gradle. I need to be able to have some tasks that execute in isolation of each other, but I cannot figure out how to do this in Gradle; for example, if I have a build.gradle that looks like the following:
apply plugin: 'eclipse'
apply plugin: 'idea'
task foo {
println 'foo'
}
task bar {
println 'bar'
}
task baz {
println 'baz'
}
If I run:
gradle -q foo
Then I expect to see
foo
But instead I see:
foobarbaz
printed to my terminal.
How can I configure Gradle to only perform the single task?
You haven't given the tasks any functionality; what you're seeing is the output of the tasks being instantiated.
Change your build.gradle to this...
task foo {
doLast {
println 'foo'
}
}
task bar << {
println 'bar'
}
task baz {
println 'baz'
}
and then run the foo task:
gradle foo
Your output should be...
baz
:foo
foo
...showing that baz was output when the baz task was created, then the foo task was executed (":foo") followed by the output of the foo task. Note that the "<<" operator is an alias for doLast.
See Build Script Basics in the Gradle User Guide.

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