这一章节主要介绍gradle命令行的基础，我们使用gradle开头的命令来运行一个构建任务
我们可以一次性运行多个gradle任务，使用空格做为每个任务之间的分隔符，比如：命令 gradle compile运行任务compile，compile test运行任务compile和任务test，其中compile和test按顺序执行（执行顺序是：compile的依赖任务-compile-test的依赖任务-test）。
注意：每个任务仅仅会被执行一次，下面举个🌰说明一下：
定义了四个任务，dist、test、compileTest、compile
依赖关系如箭头所示。dist依赖test和compile任务，test依赖compileTest和compile任务，compileTest又依赖compile任务。
task compile {
doLast {
println 'compiling source'
}
}
task compileTest(dependsOn: compile) {
doLast {
println 'compiling unit tests'
}
}
task test(dependsOn: [compile, compileTest]) {
doLast {
println 'running unit tests'
}
}
task dist(dependsOn: [compile, test]) {
doLast {
println 'building the distribution'
}
}
执行gradle dist test后的输出：
> gradle dist test
:compile
compiling source
:compileTest
compiling unit tests
:test
running unit tests
:dist
building the distribution
BUILD SUCCESSFUL in 0s
4 actionable tasks: 4 executed
执行顺序是compile compileTest test dist
每个任务仅仅执行了一次，所以gradle test test和gradle的效果是一样的
假如不需要执行test任务，则可以使用-x选项进行排除
执行gradle dist -x test后的输出
> gradle dist -x test
:compile
compiling source
:dist
building the distribution
BUILD SUCCESSFUL in 0s
2 actionable tasks: 2 executed
可以看出test任务没有被执行，test的依赖任务compileTest也没有执行。
默认情况下，gradle遇到执行出错的任务会停止执行，这样构建任务可以快速的停止，并且抛出异常。但是这样会导致未被执行到的任务的错误不能被发现。为了尽可能发现更多的错误，可以使用 --continue 选项。
当使用 --continue 选项的时候，gradle执行时遇到错误会继续执行下一个任务，并且在执行完成时在命令行末尾抛出所有错误。
如果一个任务执行失败了，那么依赖（直接或间接）这个任务的其他任务将不会被执行。
task任务的名称支持缩略形式，我们只需要提供足够的特征字符就可以。比如上边的例子，我们可以使用 gradle d 命令执行dist任务
执行gradle di命令
> gradle di
:compile
compiling source
:compileTest
compiling unit tests
:test
running unit tests
:dist
building the distribution
BUILD SUCCESSFUL in 0s
4 actionable tasks: 4 executed
也可以依照驼峰命名规则来书写缩略名称，gradle compileTest =
gradle compTest = gradle cT
gradle cT的输出
> gradle cT
:compile
compiling source
:compileTest
compiling unit tests
BUILD SUCCESSFUL in 0s
2 actionable tasks: 2 executed
使用 -x（排除） 选项时依然可以使用缩写形式。
当我们使用gradle命令时，会在当前目录下寻找build文件，我们可以使用-b选项选择其他目录下的build文件
比如说：存在文件subdir/myproject.gradle
task hello {
doLast {
println "using build file '$buildFile.name' in '$buildFile.parentFile.name'."
}
}
执行gradle -q -b subdir/myproject.gradle hello
> gradle -q -b subdir/myproject.gradle hello
using build file 'myproject.gradle' in 'subdir'.
或者我们也可以使用 -p 选项来指定整个项目目录，多项目目录使用 -p 代替 -b 选项
gradle -q -p subdir hello
> gradle -q -p subdir hello
using build file 'build.gradle' in 'subdir'.
-q 参数的作用是什么?
该文档的示例中很多地方在调用 gradle 命令时都加了 -q 参数。该参数用来控制 gradle 的日志级别，可以保证只输出我们需要的内容。
日志级别：
ERROR 错误消息
QUIET 重要的信息消息
WARNING 警告消息
LIFECYCLE 进度信息消息
INFO 信息性消息
DEBUG 调试消息
日志参数：
没有日志选项 LIFECYCLE 及更高
-q or –quiet QUIET 及更高
-i or –info INFO 及更高
-d or –debug DEBUG 及更高
-s or –stacktrace 打印关键堆栈信息
-S or –full-stacktrace 打印全栈信息
gradle内置的任务一般都是支持增量构建的，任务执行与否，取决于任务的input和output是否存在修改。如果任务不需要执行则出现 UP-TO-DATE 标识
gradle doIt
> gradle doIt
:doIt UP-TO-DATE
gradle --rerun-tasks doIt
> gradle --rerun-tasks doIt
:doIt
这个 --rerun-tasks 选项会强制执行所有任务（当前任务依赖的任务），和 clean 命令有些类似，但是不会清除构建产出。
运行 gradle projects 会以分层的形式打印出当前project的所有子project
gradle -q projects
> gradle -q projects
------------------------------------------------------------
Root project
------------------------------------------------------------
Root project 'projectReports'
+--- Project ':api' - The shared API for the application
\--- Project ':webapp' - The Web application implementation
To see a list of the tasks of a project, run gradle <project-path>:tasks
For example, try running gradle :api:tasks
可以看到打印出了子project名字和描述信息，描述信息是可以通过description属性进行设置的
比如在build.gradle文件中：
description = 'The shared API for the application'
运行命令 gradle tasks 会列出当前project的主要tasks和每个task的description
gradle -q tasks
> gradle -q tasks
------------------------------------------------------------
All tasks runnable from root project
------------------------------------------------------------
Default tasks: dists
Build tasks
-----------
clean - Deletes the build directory (build)
dists - Builds the distribution
libs - Builds the JAR
Build Setup tasks
-----------------
init - Initializes a new Gradle build.
wrapper - Generates Gradle wrapper files.
Help tasks
----------
buildEnvironment - Displays all buildscript dependencies declared in root project 'projectReports'.
components - Displays the components produced by root project 'projectReports'. [incubating]
dependencies - Displays all dependencies declared in root project 'projectReports'.
dependencyInsight - Displays the insight into a specific dependency in root project 'projectReports'.
dependentComponents - Displays the dependent components of components in root project 'projectReports'. [incubating]
help - Displays a help message.
model - Displays the configuration model of root project 'projectReports'. [incubating]
projects - Displays the sub-projects of root project 'projectReports'.
properties - Displays the properties of root project 'projectReports'.
tasks - Displays the tasks runnable from root project 'projectReports' (some of the displayed tasks may belong to subprojects).
To see all tasks and more detail, run gradle tasks --all
To see more detail about a task, run gradle help --task <task>
仅仅是展示了分组下的task（包括子project的task），称作可见task，我们可以给task指定group属性，当然和project类似，也存在description属性。
build.gradle
dists {
description = 'Builds the distribution'
group = 'build'
}
使用 --all 选项，可以查看所有的task
gradle -q tasks --all
> gradle -q tasks --all
------------------------------------------------------------
All tasks runnable from root project
------------------------------------------------------------
Default tasks: dists
Build tasks
-----------
clean - Deletes the build directory (build)
api:clean - Deletes the build directory (build)
webapp:clean - Deletes the build directory (build)
dists - Builds the distribution
api:libs - Builds the JAR
webapp:libs - Builds the JAR
Build Setup tasks
-----------------
init - Initializes a new Gradle build.
wrapper - Generates Gradle wrapper files.
Help tasks
----------
buildEnvironment - Displays all buildscript dependencies declared in root project 'projectReports'.
api:buildEnvironment - Displays all buildscript dependencies declared in project ':api'.
webapp:buildEnvironment - Displays all buildscript dependencies declared in project ':webapp'.
components - Displays the components produced by root project 'projectReports'. [incubating]
api:components - Displays the components produced by project ':api'. [incubating]
webapp:components - Displays the components produced by project ':webapp'. [incubating]
dependencies - Displays all dependencies declared in root project 'projectReports'.
api:dependencies - Displays all dependencies declared in project ':api'.
webapp:dependencies - Displays all dependencies declared in project ':webapp'.
dependencyInsight - Displays the insight into a specific dependency in root project 'projectReports'.
api:dependencyInsight - Displays the insight into a specific dependency in project ':api'.
webapp:dependencyInsight - Displays the insight into a specific dependency in project ':webapp'.
dependentComponents - Displays the dependent components of components in root project 'projectReports'. [incubating]
api:dependentComponents - Displays the dependent components of components in project ':api'. [incubating]
webapp:dependentComponents - Displays the dependent components of components in project ':webapp'. [incubating]
help - Displays a help message.
api:help - Displays a help message.
webapp:help - Displays a help message.
model - Displays the configuration model of root project 'projectReports'. [incubating]
api:model - Displays the configuration model of project ':api'. [incubating]
webapp:model - Displays the configuration model of project ':webapp'. [incubating]
projects - Displays the sub-projects of root project 'projectReports'.
api:projects - Displays the sub-projects of project ':api'.
webapp:projects - Displays the sub-projects of project ':webapp'.
properties - Displays the properties of root project 'projectReports'.
api:properties - Displays the properties of project ':api'.
webapp:properties - Displays the properties of project ':webapp'.
tasks - Displays the tasks runnable from root project 'projectReports' (some of the displayed tasks may belong to subprojects).
api:tasks - Displays the tasks runnable from project ':api'.
webapp:tasks - Displays the tasks runnable from project ':webapp'.
Other tasks
-----------
api:compile - Compiles the source files
webapp:compile - Compiles the source files
docs - Builds the documentation
