In an effort to convert some metadata source to the appropriate Source format to apply to a scratch org, I ran this command within my project directory:

sfdx force:mdapi:convert --rootdir mdapi_project --outputdir tmp_convert

in which '--rootdir' and '--outputdir' are specific folder locations within the same project directory.

My result is this error:

ERROR running force:mdapi:convert:  Unexpected arguments: --rootdir, mdapi_project, --outputdir, tmp_convert

Why does this happen? And how to resolve?

--outputdirz

Use Case: if certain field values on a User record changes, I want that change to appear in corresponding fields on all the Contact records that this user owns.

I figure I need to create this trigger on the User object, but how do I call that User's Contact records to update their values?