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Using sftp on the command line, with or without a proxy

· 3 min read
Christophe
Christophe
Markdown, WSL and Docker lover ~ PHP developer ~ Insatiable curious.

Using sftp on the command line, with or without a proxy

After my article SSH - Launch a terminal on your session without having to authenticate yourself, it was obvious that, next to the ssh and scp commands, I forgot the sftp one.

In this article, we'll explore how to start a SFTP connection to a remote server; from the command line.

In the second section, we'll also learn how to configure the sftp connection to use a proxy server.

How to run a sftp connection​

The easiest way is sftp <username>@<hostname_or_ip> so, if you need to connect to the server having the IP 1.2.3.4 with the user christophe, the command to start is simply sftp christophe@1.2.3.4.

You'll be prompted to enter your password before being connected to the server.

If you need some automation, you can install sshpass using sudo apt-get update && sudo apt-get install sshpass.

note

The sshpass Linux utility is used by the script to allow a SFTP connection without to have to use the password in plain-text. Get more info

Let's imagine your user is christophe, your password is p@ssword and the server IP is 1.2.3.4 then you can connect to your user like this: SSHPASS="p@ssword" sshpass -e sftp christophe@1.2.3.4.

Here above, we're creating a temporary OS variable called SSHPASS with our password in plain text then run sshpass -e followed by our sftp command so sftp <username>@<hostname_or_ip>.

Using a proxy server​

Using a proxy is not so intuitive. The flag to use is -o ProxyCommand='' and a specific command. The command is /usr/bin/nc --proxy-type http --proxy PROXY:PORT %h %p where:

  • proxy-type should be initialized to http or https depending on your proxy.
  • --proxy should be set to the proxy domain name (f.i. my.proxy.be) and perhaps followed by :8080 i.e. the port to use
  • then %h %p should be part of the command
    • %h is a placeholder that will be replaced by the hostname of the SFTP server you're trying to connect to.
    • %p is another placeholder that will be replaced by the port number of the SFTP server.

The final command will looks something like:

sftp -o ProxyCommand='/usr/bin/nc --proxy-type http --proxy my.proxy.be:8080 %h %p' christophe@1.2.3.4

And, if you want to use sshpass:

SSHPASS="p@ssword" sshpass -e sftp -o ProxyCommand='/usr/bin/nc --proxy-type http --proxy my.proxy.be:8080 %h %p' christophe@1.2.3.4

Setting the port number to use for the SFTP server​

If your SFTP server is not running on port 22, you'll need to specify the port number by using the -P flag: sftp <username>@<hostname_or_ip> -P <port_number>.

Running commands on the SFTP server then exit​

Imagine you wish to retrieve ZIP files from your SFTP server.

As already seen, using sshpass we can bypass the authentication. We just need to make sure a SSHPASS variable exists just before calling the sshpass command.

Then, to be able to automate some commands on the SFTP server, we can use a here-document syntax.

The general look&feel will be this one:

(
    SSHPASS="<your_password_in_plain_text>"
    sshpass -e sftp <username>@<hostname_or_ip> << !
        <a_list_of_commands>
!
)

So, if your user is christophe, your password is p@ssword and the server IP is 1.2.3.4, we can connect to the server and, for instance, jump in a folder called input_folder then display the list of files / folders and, finally, download all zip files present in the folder:

(
    SSHPASS="p@ssword"
    sshpass -e sftp christophe@1.2.3.4 << !
        cd input_folder
        ls -alh
        get *.zip
!
)