SFTP / SCP using password

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http://www.unix.com – Hi, I was provided with sftp servername, user and password and the requirement is to connect to sftp server using credentials provided and drop the file. Manually i am able to connect with commands like sftp user@servername and after clicking enter, i was asked for a password and entering the password i am able to get it the remote server. How can i do the same using scripts i.e when i execute the script, it should connect to server using credentials ( without any manual interverntion )? I used to do these sftp connections via key exchange ( public key deployed to remote server ) but not (HowTos)