Java command line options for Clojure CLI

whats the difference between

-Jopt Pass opt through in java_opts, ex: -J-Xmx512m
-Oalias... Concatenated jvm option aliases, ex: -O:mem

https://clojureverse.org/t/how-to-pass-jvm-opts-to-clj-from-terminal/1940/3?u=drewverlee

ClojureVerseClojureVerse
How to pass :jvm-opts to clj from terminal?

The -O flag is used to pass alias names, not options. So one choice is to create an alias: :aliases {:xb {:jvm-opts ["–add-modules java.xml.bind"]}} then activate the alias at the command line: clj -O:xb ...etc...

Supply jvm options directly in the command line with -J: clj -J–add-modules java.xml.bind ...etc...

aliases are a feature of tools.deps, where you can kind of group alternative configurations together and give them a name, and -O lets you apply them

-J is for passing arguments directly to the command that launches the jvm, typically 'java'

What would it look like to psas multiple arguments to the jvm? each one gets a J-

clojure J- J-

it is passing options, flags like -Xmx512m

so for example, you could pass -J-server (which is the default these days)

so for multiple its like clojure ... -J-Xmx512m -j-Xms512

clojure -J-Dfoo=bar -J-Dquux=wibble
Clojure 1.10.1
user=> (System/getProperty "foo")
"bar"
user=> (System/getProperty "quux")
"wibble"
user=> ^D

One -J per argument you want to pass. Beware of white space

some arguments are for scripts, some for jvms, and some for clojure, and some for your code
00:02
clj/clojure also have another of different ways to combine aliases, but -A will usually do want you want

(aliases can also specify jvm options, and -O combines those ignoring the other stuff specified in the aliases)

Start with the clj/clojure command-line entry points and the -J and -O options described in the issue. Compare them with the linked ClojureVerse explanation, including how multiple JVM arguments are passed. Done means the documentation clearly distinguishes direct JVM options from alias-based options and shows the correct repeated-flag syntax.