$ sftp -i /home/ubuntu/.ssh/yourprivatekeyfile loginname@ssome.server.com
 
sftp>

echo ls -alt | sftp someserver > somehost_available_files.txt
 
Connected to someserver.

echo get somefile.csv | sftp someserver

echo "ls -alt | grep ^someprefix_" | sftp someserver > somehost_available_files.txt
 
$ while read FILE; do echo "Downloading $FILE..."; echo "get $FILE" | sftp someserver; done < somehost_available_files.txt

sftp hostaspersshconfig << EOF
get *
quit
EOF