The file .pgpass in the home directory is a file that can contain passwords to be used if the connection requires a password. This file should have the format:
hostname:port:database:username:password
Any of these may be a literal name, or *, which matches anything. The first matching entry will be used, so put more-specific entries first. When an entry contains : or \, it must be escaped with \.
The permissions on .pgpass must disallow any access to world or group; achieve this by the command chmod 0600 .pgpass. If the permissions are less strict than this, the file will be ignored.