JEP proposed to target JDK 11: 330: Launch Single-File Source-Code Programs

[Peter Levart]

Hi,

If this JEP added a feature that specifying source file name as "-" 
would read STDIN as the Java source file, one could write executable 
scripts in the following "hybrid" way:

#!/bin/bash

exec /path/to/java - $* <<EOF

public class Hello {
     public static void main(String[] args) {
         System.out.println("Hello world");
     }
}

EOF


Notice that this does not need shebang support from java launcher. The 
benefit of this approach would also be that /path/to/java could be 
computed by the bash script prefixing the Java source. Java typically 
does not have a standard installation "place" like bash, so shebang 
scripts with hard-coded java path would be less portable as bash 
scripts. Of course one could do something similar with the following 
trick (using support for shebang in java launcher):

#!/bin/bash
//bin/true; JAVA_HOME=<computed path> exec $JAVA_HOME/bin/java $0 $*

public class Hello {
     public static void main(String[] args) {
         System.out.println("Hello world");
     }
}


..but this still needs shebang support and script author is forced to 
use a special prefix in each line of bash script prefixing the java source:

//bin/true; ...
//bin/true; ....
//bin/true; ...



Support for "-" STDIN source in java launcher does have one drawback. 
Scripts written this way can not process STDIN passed to the script as 
STDIN of java launcher is redirected to obtain Java source.

Regards, Peter