Update Sep 2017 – tl;dr
Download a single file from a remote ftp server to your machine:
sftp {user}@{host}:{remoteFileName} {localFileName}
Upload a single file from your machine to a remote ftp server:
sftp {user}@{host}:{remote_dir} <<< $'put {local_file_path}'
Original answer:
Ok, so I feel a little dumb. But I figured it out. I almost had it at the top with:
sftp user@host remoteFile localFile
The only documentation shown in the terminal is this:
sftp [user@]host[:file ...]
sftp [user@]host[:dir[/]]
However, I came across this site which shows the following under the synopsis:
sftp [-vC1 ] [-b batchfile ] [-o ssh_option ] [-s subsystem | sftp_server ] [-B buffer_size ] [-F ssh_config ] [-P sftp_server path ] [-R num_requests ] [-S program ] host
sftp [[user@]host[:file [file]]]
sftp [[user@]host[:dir[/]]]
So the simple answer is you just do : after your user and host then the remote file and local filename. Incredibly simple!
Single line, sftp copy remote file:
sftp username@hostname:remoteFileName localFileName
sftp kyle@kylesserver:/tmp/myLogFile.log /tmp/fileNameToUseLocally.log
Update Feb 2016
In case anyone is looking for the command to do the reverse of this and push a file from your local computer to a remote server in one single line sftp command, user @Thariama below posted the solution to accomplish that. Hat tip to them for the extra code.
sftp {user}@{host}:{remote_dir} <<< $'put {local_file_path}'