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From Maarten Boekhold <>
Subject Trick: using groovy script as a "shell script" on UNIX
Date Tue, 02 Jun 2015 09:25:29 GMT
Hi all,

I recently discovered a neat trick to create a standalone groovy script 
on UNIX that you can run as if it was a shell/bash script. The first 
part of the trick I got from the following StackOverflow post:

You can "embed" a groovy script inside a bash script as follows:

    //usr/bin/env /path/to/groovy "$0" @0; exit $?

    println "My groovy script"

This launches a bash shell that runs the groovy interpreter /on this 
same file/ ("$0"), because "//usr/bin/env" is just equivalent to 
"/usr/bin/env" (eg the double leading slash is collapsed to a single 
slash by bash). Groovy ignores the first line if it starts with a #, and 
the second line starts with // which is a comment in groovy.

If you need to add classpath entries or java properties or any other 
command line options to groovy, you can insert them on that second line 
as well of course, but that can generate quite a long and unreadable 
line if you have a lot of entries. However you can use the same "// 
trick" to set environment variables /before/ you launch groovy:

    //usr/bin/true && export CLASSPATH=....
    //usr/bin/true && export OPTS="-Dmy.opt1=foo -Dmy.opt2=bar"
    //usr/bin/true && export OPTS="$OPTS -Dmy.opt3=foobar"
    //path/to/groovy $OPTS "$0" @0; exit $?

    println System.env[my.opt1]

Note that on the line starting groovy you don't even need to prefix it 
with //usr/bin/env as long as you use a fully qualified path to the 
groovy interpreter. If you want bash to find groovy in your PATH however 
you do need that //usr/bin/env prefix.

Neat eh? Maybe we can include this in the documentation somewhere?


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