problems restoring database from plain text backup from psql

One more thing to mention is that this database is PostGIS enabled. So I
had to remove all CREATE FUNCTION commands in the backup file.
In the mean time I tried to restore with psql:
psql mydb < mybackup.sql -U postgres
Unfortunately I have no possibility to enter my password
Somehow password is entered automatically and prompt jumps over the
place where password should be entered. I am getting:
"psql: FATAL: password authentication failed for user "postgres""
Best regards
Oleg