How to create a database from shell command?

You mean while the mysql environment?

create database testdb;

Or directly from command line:

mysql -u root -e "create database testdb"; 

cat filename.sql | mysql -u username -p # type mysql password when asked for it

Where filename.sql holds all the sql to create your database. Or...

echo "create database `database-name`" | mysql -u username -p

If you really only want to create a database.