I have a trailhead playground org (not a scratch org) for which I've created multiple aliases and now I'd like to know how I can keep one and delete all the others using the Salesforce CLI? Also, is there a command that allows renaming an org's alias?
To see all the orgs you have with the aliases associated use the command:
To see all aliases you set:
To remove the alias alone, you can use the command:
sfdx alias:unset <aliasName1> <aliasName2> <aliasName3> ...
this will remove the alias, but keep the org.
If you want to remove the org you can logout of the org using:
sfdx force:auth:logout -u <aliasOrUsername>
this will remove it from your list until you authorize it again.
to rename an alias, you can use the command
sfdx alias:set <newAlias>=<usernameOrValue>
if the org already has an alias, I don't believe that the newAlias will override that alias displayed in your org list, so best way to go about it would be to first unset the alias for a username and then reset it as necessary.
hope that helps answer your question.
Salesforce CLI Command Reference