I'm using the library sshj for sending an scp command. It uses the option -f for downloading from a server to another. I can't find the -f option in the man.
What is the signification of -f in an scp command?
-f and -t are undocumented switches which tell the remote scp to send or prepare to receive a file or files from the local scp.
This site explains it in slightly more detail in section 3.8.1. scp1 Details:
That copy is invoked with the undocumented switches -t and -f (for "to" and "from"), putting it into SCP1 server mode. This next table shows some examples; Figure 3-6 shows the details.
This client scp command: Runs this remote command: scp foo server:bar scp -t bar scp server:bar foo scp -f bar scp *.txt server:dir scp -d -t dir