To save the mysql username & password you use via command line, use the following;
Add ~/.my.cnf file with the following content
[Client]
user=myusernamehere
password=mypasswordhere
host=localhost
database=mydbnamehere
For DB Dumps via command line (in *nix);
Compressing;
mysqldump dbname | gzip -c > myfilename.sql.gz
Resoring DB;
gunzip -c myfilename.sql.gz | mysql dbname