Shell (general)

This section talks about some Groovy features handled by this shell and how to use them.

This shell can use most of Groovy SDK. It is based on Groovy 2.4.XX. The version used will be displayed when you’ll start the shell.

You can use groovy syntax features, write functions, call them, define classes instantiate objects… You can also use Java classes such as LocalDateTime, Instant and even Streams. Groovy syntax is compatible with Java syntax, but note that it doesn’t support Java lambda expression syntax. Use closure instead (e.g { Object o -> println(o) }).

Groovy meta-programming also works. You can define, override method of classes/objects at runtime. To perform that, check the Groovy documentation

Variable declarations

Be careful with variable declaration. If you put the type (or def) before the variable, you submit the code (a prompt) and then try to access the same variable, it won’t exist anymore. If you want to keep the variable after you submitted your code you’ll have to omit the type/def.

The following example will not work images prompts

def a = 2
String variable = "some value"

then prompts

// will throw an exception because shell doesn't know 'a' and 'variable' anymore
a == variable

Here is the proper way to declare variables if you want to keep them in your next prompts

a = 2
variable = "some value"

Imports

Here is an example of import Example:

import java.nio.file.Path

In addition, of Groovy default imports, here is the list of package imported by default in this shell

java.time.*
java.time.format.*
java.util.concurrent.*
groovy.json.*
groovy.xml.*
java.nio.file.*
java.util.zip.*
java.util.regex.*
java.nio.file.*
java.util.concurrent.atomic.*

Furthermore, you can import many packages (and enums) with import aliases

Ask permission

In order for the app to perform I/O operations, you’ll need to grant some permissions. The available permissions depend on the version of your Android device (which is displayed everytime you start a new shell).

Pre Android 11

Android restricts the app access to files. To grant this permission, you’ll need to ask permission like in the following example.

permission = Permissions.WRITE_EXTERNAL_STORAGE
requestPermission(permission)

If you want to ask all permissions, you can enter

requestPermission(*PERMISSIONS)

Here is the list of permissions you can ask

• WRITE_EXTERNAL_STORAGE
• READ_EXTERNAL_STORAGE
• ACCESS_NETWORK_STATE

You can also see granted permissions in the preferences screen.

Post Android 11

Since Android 11 new restrictions, a the READ/WRITE_EXTERNAL_STORAGE permissions became useless, they have been replaced by the MANAGE_EXTERNAL_STORAGE, allowing to read AND write to external storage. To request this permission, you’ll need to request READ_EXTERNAL_STORAGE and/or WRITE_EXTERNAL_STORAGE (they are treated as same permissions, post Android 11), but note that you’ll need to request these file permissions separatly from others

// requesting file permissions
requestPermission(Permissions.WRITE_EXTERNAL_STORAGE)
// *prompt*
// then requesting other permission
requestPermission(Permissions.ACCESS_NETWORK_STATE)

Class definition

You can define classes. When you do so, by default, you can’t put any other instructions after in the same prompt, they won’t be processed (yeah, this is weird but this is how it works). You CAN put other instructions only if between the class definition and the rest, you put special the comment/*PROMPT*/. To get instances from the defined class, you’ll need to use java.reflect methods. You can construct instances with the syntax a = new A(). Also, all defined classes will appear in the variable CLASSES, a map of class name -> class.

e.g:

Class definition

class A {
 int b
}

Getting instances

a = new A()
a2 = new A(b: 1)
a3 = CLASSES.A.newInstance()
a4 = CLASSES.A.newInstance(b: 1)

Special comment /*PROMPT*/

This comment allows you to define classes in a script/shell works, or even defining multiple classes.

Defining multiple classes and doing things after (in a same prompt)

int value = 2
doSomething()
/*PROMPT*/
class A {
 int b
}
/*PROMPT*/
class B {
 int a
}
/*PROMPT*/
a = new A(b: value)
b = new B()
/*PROMPT*/
doSomething(a, b)

Standard Input (STDIN)

You can also write programs using the standard input with the help of the System.console() (or variable console)

input = System.console().readLine 'Enter some input'

In the above example, the String passed in a parameter will be displayed in the standard output (in the shell, like a println would), then You’ll have to enter some input. The text color should be blue when entering some input in STDIN. Click the prompt button when finished, to submit the text to STDIN.

So you can write scripts that takes input data.