[Feat] g.proj printing in json format for easier parsing

[baharmon]

Is your feature request related to a problem? Please describe.

The GRASS Tools API is supposed to make parsing of tool output easier with Python, but it is now harder for g.proj. Flag g is depreciated and this module suggests using format=shell instead, but in Python that returns a ToolResult object that takes more work to parse. The ToolResult can be returned as a dictionary with method .keyval, but the manual page for this tool does not have an example of this.

# Find units with depreciated flag
projection = gs.parse_command("g.proj", flags=["g"])
units = projection.get("units", "units")

# Find units with shell
projection = tools.g_proj(format="shell", flags="p").keyval
units = projection.get("units")
print(units)

Describe the solution you'd like

I suggest adding a format=json option to g.proj for easier parsing. I also suggest adding up to date examples of parsing results with Python to the manual page.

# Find units with JSON
units = tools.g_proj(format="json", flags="p")["units"]
print(units)

Additional context
GRASS 8.5.0 (2026)

[petrasovaa]

What about projjson format option? See some earlier discussions in the PRs this was implemented, but if I remember correctly, we decided to use the standardized PROJJSON.

[baharmon]

PROJJSON format is much harder to parse and does not serve as a good replacement for flag -g. Adding a regular json format would make it more consistent with other tools and easier to parse.

# Find units with PROJJSON
projection = tools.g_proj(format="projjson", flags="p")
axis = projection["coordinate_system"]["axis"]
units = [a.get("unit") for a in axis]
print(units[0])

metre

Here is the discussion from the pull request implementing projjson format: #6614. The arguments for projjson replacing json are strong being based on standards, but do not address the depreciation of flag g and replacement with shell format. Vaclav's counter argument that "if we say the current format="json" is wrong, we should also remove format="shell" (and change the reason why -g is deprecated)" still stands. Standards are good, but so is usability. With g.proj users need an option to easily parse output.