Groovy's ecosystem has grown to fantastic dimensions over the last years. There are libraries and frameworks for virtually every job you can imagine. What is less commonly known is that Groovy can serve as a very efficient and convenient tool on the commandline as well. We will begin with a very brief introduction how to run Groovy on the command line. We will then move on to topics like pipes and FIFOs for command line tools interop, dependency management and testing. In the end you will know the tools required to write effective and well-tested shell scripts in Groovy that can utilize the full power of the JVM's library ecosystem.

1. Making shell scripts Groovy

2. about me
● programmer + DevOps enthusiast
– Java, Groovy, learning Clojure
– Linux, Ansible, Liquibase, Maven
● co-organizing software craftsmanship groups:
– Ruhrgebiet + Düsseldorf (Germany)
– coderetreats, coding dojos
georgberky
georg.berky@valtech-mobility.com

3. my journey to Groovy
● problem in production
● when contacting a remote system via HTTP
● not enough logging
● but access to the machine
● everything works in curl

4. my journey to Groovy
● problem has to be inside the JVM
● google: “run Java as a script”
● Groovy!
● some tinkering, some dependencies
● ⇒ missing certificate in Java’s keystore :)

5. today’s agenda
● shebang + groovyserver
● pipes
● dependency management
● parameter parsing
● external commands
● bonus: XML/JSON
● bonus: FIFOs
● bonus: logging

6. setup
● install sdkman from sdkman.io
● install groovy using sdkman
– groovy --version should work
● use your favorite editor
● Groovy API
http://docs.groovy-lang.org/latest/html/gapi/
● JDK extensions:
http://groovy-lang.org/gdk.html

7. getting started
● start with shebang + make executable
● write “hello world” in Java
● use file extension: .groovy
● run: ./HelloWorld.groovy
● leave out as many syntax elements as you can

8. pipes
● connect two processes
● live outside your root file system
● lifetime: as long as the process creating it
● writing end + reading end
● ends support UNIX file interface

9. protocol for pipes
● one line is one message
● line buffered
● last producer disconnects: EOF
● preserve order

10. exercise: using pipes
● write a program that mimics grep
– e.g. grep groovy < input.txt
● read lines from System.in
– hint: use eachLine
● print line if it contains the argument
– hint: use args[0]

11. testing
● batteries included: JUnit 3 – 5
● power assert
● test doubles: closure + map coercion
● MockFor, StubFor
only in dynamic context
scripts: compiled

12. exercise: testing
● FizzBuzz Kata
● print all numbers from 1 to 100
● if n divisible by 3, print fizz
● if n divisible by 5, print buzz
● if n divisible by 3 and 5, print fizzbuzz

13. dependency management
● @Grab(‘org.apache.commons:commons-lang3:3.9’)
● @Grab(group='org.apache.commons',
module='commons-lang3',
version='3.9')
● at runtime: Grape.grab(
group:’org.apache.commons’,
module:’commons-lang3’,
version:’3.9’)

14. dependency management
● Groovy Grape
● built on top of Apache Ivy
● grabs (transitive) dependencies
– default: from Maven Central
● scripts: replaced with Grape.grab()
– in static initializer

15. command line options
● Groovy Commons CliBuilder
● @Grab(group='org.codehaus.groovy',
module='groovy-cli-commons',
version='2.5.7')
● import groovy.cli.commons.CliBuilder
● supports short and long options
● now supports typed arguments

16. exercise: parsing arguments
● use:
@Grab(group='org.codehaus.groovy',
module='groovy-cli-commons',
version='2.5.7')
● extend your grep script:
● ignore case: -i
● invert matching: -v

17. external commands
● method execute() on String
● e.g. “ls -1”.execute()
● creates and runs instance of Process
● method getText() on Process,
then method eachLine() on String

18. final assignment
● Producer: prints numbers, one per line
● Consumer: read lines
– increment the number
– print the incremented number
● communicate via pipe
● separate concerns
● test drive as much as you can

19. suggested design

20. final assignment - hints
● Isolated tests:
– Map coercion for mocks:
[methodName: { … }] as Interface
– @Grab Mockito for mocks
● integrated tests:
– getInputStream() on Process
– getOutputStream() on Process
●

21. got interested?
● Previous work: Sascha Klein - “Groovy on the Shell”
– https://tinyurl.com/groovy-on-the-shell
● Georg Berky - “Groovy Shell Scripting”
(Never Code Alone Blog)
– http://tinyurl.com/groovy-shell-1
– http://tinyurl.com/groovy-shell-2
– http://tinyurl.com/groovy-shell-3
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22. thank you!
georgberky
georg.berky@valtech-mobility.com