Is it possible to rate-limit an scp/sftp/rsync/etc transfer from the command-line? ie, manual QoS on a single command?

Specifically, I am looking to rate-limit an scp or sftp session (or other arbitrary network call) in the call itself.

For example, let's say I want to copy 100MB to one server, and 1GB to another. I'd like to be able to run both of these at the same time, but maintain a QoS for "normal" computer usage - somewhat similar to how you can rate-limit bittorrent.

Is there a way to do this without touching the networking hardware?

I'm envisioning something akin to:

magic-qos-tool 'scp file user@host:/path/to/file'

Or..

scp -rate 40kbps file user@host:/path/to/file

Yes, there's an application that works exactly like your 'magic-qos-tool', called "trickle".

EXAMPLES
     trickle -u 10 -d 20 ncftp

     Launch ncftp(1) limiting its upload capacity to 10 KB/s, and download ca-
     pacity at 20 KB/s.

scp has -l, and rsync has --bwlimit.

Rsync makes this easy on you, it has an option to do this: --bwlimit=KBPS

sftp has a throttle flag, as of Debian 7 and Ubuntu 12.04 in those distributions:

-l limit

Limits the used bandwidth, specified in Kbit/s.

(Of course that's a lower case L.)

Source: stfp(1)