How to set up temporary path for starting up psql in any folder?
I do not want to disrupt existing settings of paths.
This isn't really a Pg SQL question so I think you're posting to the wrong group. Doing what you want depends on the OS but it's pretty easy to append to a path without overwriting the user account-defined paths on the current console. Or you can create some kind of system batch file that you can use to load Pg which will add the paths you want and then load psql and then unset the paths afterwards.. You might try superuser for help on setting paths and creating batch files along these lines?
