RFR: 8340133: Add concise usage message to the java executable [v5]

[Jan Lahoda]

On Tue, 22 Oct 2024 11:06:44 GMT, Jan Lahoda <jlahoda at openjdk.org> wrote:

>> Currently, running `java` without any parameters will lead to an output that is a full `--help`, which is over 100 lines (on my computer at least), and it feels overwhelming. And many people might actually want to run JShell/REPL, not the `java` executable, but it is difficult find out about JShell.
>> 
>> The proposal herein is to print a much shorter help, together with a pointer to JShell, when the executable does not know what to do. I.e. there is nothing specified to start, and no option like `--help` is specified. In particular, on my machine, it prints:
>> 
>> openjdk 24-internal 2025-03-18
>> 
>> Usage: java [java options...] <application> [application arguments...]
>> 
>> Where <application> is one of:
>>   <mainclass>                to execute the main method of a compiled class
>>   -jar <jarfile>.jar         to execute the main class of a JAR archive
>>   -m <module>[/<mainclass>]  to execute the main class of a module
>>   <sourcefile>.java          to compile and execute a source-file program
>> 
>> Where key java options include:
>>   --class-path <class path>
>>     where <class path> is a list of directories and JAR archives to search for class files, separated by ":"
>>   --module-path <module path>
>>     where <module path> is a list of directories and JAR archives to search for modules, separated by ":"
>> 
>> For additional help on usage:           java --help
>> For an interactive Java environment:    jshell
>> 
>> 
>> Hopefully, this may be easier both for people trying to run something, and for people that are really looking for JShell.
>> 
>> What do you think?
>> 
>> Thanks!
>
> Jan Lahoda has updated the pull request incrementally with one additional commit since the last revision:
> 
>   Cleaning up the concise message:
>   - using 2 spaces instead of 4,
>   - rewording the "for more use --help" part of the message as suggested to avoid the word "launcher".

> > The file separator is a secondary concern and could be moved to the end of the sentence:
> > ```
> > Where key java options include:
> >   --class-path <class path>
> >       a list of directories and JAR archives to search for class files, separated by ":"
> >   --module-path <module path>
> >       a list of directories and JAR archives to search for modules, separated by ":"
> > ```
> 
> I agree with this comment. I also have another observation - it is not super obvious that "a list of directiories ..." is a description for what a or is. You kind of guess that being the case (what else can it be?) but something like:
> 
> ```
>  --class-path <class path>
>         where <class path> is a list of directories and JAR archives to search for class files, separated by ":"
> ```
> 
> Seems more crystal clear?
> 
> (Btw, the reason I like moving `:` at the end is that you want users to quickly graps what is - and this trick does that: "a class path is a list of directories and jars" - whether they're `:` or `#!?` separated, that's a second-order concern at this point (as we're still defining the term).

Ok:
https://github.com/openjdk/jdk/pull/21411/commits/f1f7cc8006dcd2bdefe5bbc90936c6ccbdf044ab

(text in the description updated)

I checked, and the default line length for `cmd` on Windows 10 appears to be 120 characters. the longest line is now 108 characters long. So, we are nearing the hard-limit for the text.

I also start to wonder if adding the text for these options lights its weight, and whether it wouldn't be better to just skip the options, leading to a leaner, shorter help.

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PR Comment: https://git.openjdk.org/jdk/pull/21411#issuecomment-2437683715