Pass Custom Private Key in SFTP Using SSH Options

To pass custom private key (custom identity file, rather than the default one from .ssh directory) when connection via sftp, use the following command:  

sftp -v -oIdentityFile=/path/to/custom/.ssh/id_rsa  username@www.serverexample.com

The “-v” option will print out verbose debugging information, “-o” allows us to pass ssh options, in this case we pass “IdentityFile” with value “/path/to/custom/.ssh/id_rsa”.