These repro steps assume you have godot available in your $PATH under the name godot. If not, replace godot with an absolute path to your Godot 3.0.2 binary.

It also assumes your current working directory is the root of this repo.

godot --help states the following:

--path Path to a project ( must contain a 'project.godot' file).

This seems to be wrong.

1. run godot --path pong/project.godot

Note that the project selector menu shows. Close godot.

2. run godot -path pong/project.godot

Now the actual project passed in opens directly.

1. run godot -path pong/project.godot --export "HTML5" dist/

Output:

exporting res://pong.tscn
ERROR: EditorExportPlatform::save_pack: Condition ' !f ' is true. returned: ERR_CANT_CREATE
   At: editor\editor_export.cpp:818

Assumed error: godot is unable to create the folder

2. run mkdir dist
3. run godot -path pong/project.godot --export "HTML5" dist/

Same output.

4. run mkdir dist
5. run godot -path pong/project.godot --export "HTML5" dist/index.html

Same output.

0. delete dist folder if made in previous step (rmdir dist)
1. run godot -path pong/project.godot --export "HTML5" $(pwd)/dist/

Output:

ERROR: EditorExportPlatform::save_pack: Condition ' !f ' is true. returned: ERR_CANT_CREATE
   At: editor\editor_export.cpp:818

Assumed error: godot is unable to create the folder:

2. run mkdir dist
3. run godot -path pong/project.godot --export "HTML5" $(pwd)/dist/

Export seems fine.

Content of dist:

$ ls -al dist/
total 11508
drwxr-xr-x 1 Karl 197121        0 May  7 19:52 ./
drwxr-xr-x 1 Karl 197121        0 May  7 19:52 ../
-rw-r--r-- 1 Karl 197121   338820 May  7 19:52 .js
-rw-r--r-- 1 Karl 197121    16116 May  7 19:52 .pck
-rw-r--r-- 1 Karl 197121 11422500 May  7 19:52 .wasm

Assumption: --export requires a output name.

4. Delete dist, and recreate folder rm -r dist && mkdir dist
5. run godot -path pong/project.godot --export "HTML5" $(pwd)/dist/index

Content of dist

$ ls dist/
index  index.js  index.pck  index.png  index.wasm

Assumption: Output requires .html?

6. Delete dist, and recreate folder rm -r dist && mkdir dist
7. run godot -path pong/project.godot --export "HTML5" $(pwd)/dist/index.html

$ ls dist
index.html  index.js  index.pck  index.png  index.wasm

Output seems correct.

However, running this on a Linux based OS yields the following output:

root@ee0f98ff81a0:~/project# ls dist
index.pck