Given that Java 9 is upon us and we can finally have a java REPL with jshell I was hoping there was a way to add a shebang to a script and have jshell interpret it.
I tried creating test.jsh:
#!/usr/bin/env jshell -s
System.out.println("Hello World")
/exit
However that gives:
⚡ ./test.jsh
| Error:
| illegal character: '#'
| #!/usr/bin/env jshell -s
| ^
| Error:
| illegal start of expression
| #!/usr/bin/env jshell -s
| ^
Hello World
It turns out there is an enhancement request for this in OpenJDK https://bugs.openjdk.java.net/browse/JDK-8167440.
Is there any other way to do this?
Use
//usr/bin/env jshell --show-version --execution local "$0" "$@"; exit $?
as the first line of test.jsh. The test.jsh script could look like:
//usr/bin/env jshell --show-version "$0" "$@"; exit $?
System.out.println("Hello World")
/exit
The command line option --show-version is optional, of course, but gives immediate feedback that the tool is running.
The extra command line option --execution local prevents jshell to spawn another VM. This speeds up launch time and if an exception is thrown by your script code, the local VM will exit.
Consult the output of jshell --help and jshell --help-extra for more options.
Update
Also take a look at https://github.com/maxandersen/jbang Having fun with Java scripting, which offers a neat wrapper around running .java files from the command line.
It turns out that with a bit of trickery there is a way, although I haven't fully managed to suppress the interpreted commands but pretty close to what I want.
Change test.jsh to:
#!/usr/bin/env sh
tail -n +4 "$0" | jshell -s "$@"
exit $?
System.out.println("Hello World")
/exit
Which gives us:
⚡ ./test.jsh
-> System.out.println("Hello World")
Hello World
-> /exit
Inspired by steiny answer, I came up with a more generic solution
https://gist.github.com/ffissore/012d7e32a096fde5266f49038c93dcaf
In essence: jshell-wrapper will strip the first line of the script (which is supposed to be the shebang) and will add a /exit at the end of the script
