Using Here-Document as password Input for ssh

Question

First, I do know this is a security risk. I do know about ssh keys and sshpass. This belongs to a fun project.

I wondered if a bash Here-Document could be used as a password input for ssh.

I unseccessfully tried something like

ssh localhost <<!
mytestpasswd
/bin/bash
!

Sadly the bash terminates. I belive it's because the Here-Document closes stdin.

Did someone figure out how to achieve this?

Answer 1

You're right that a simple here-document won't work for SSH password input because SSH reads passwords directly from the terminal /dev/tty, not from stdin.

• Why heredoc does not work for sftp password?

• Can I use a heredoc to enter a password in bash?

You can use expect, a tool designed for automation to achieve this in a fun project.

• Expect Script SSH Example Tutorial

• Expect script for remote SSH login and executing commands

If you don't want to write an expect script, you can use sshpass in a one-liner.

sshpass -ffilename ssh user@host                                # prefer this
SSHPASS=$(secret-tool lookup mypasswd) sshpass -e ssh user@host # or this
sshpass -pPa5sw0rd ssh user@host                                # avoid this

• How to specify password in ssh command

• sshpass – Login to ssh server with a password using a shell script

• How to automate SSH login with password?

Both sshpass and expect are external tools and not part of Bash itself. The original point was more about syntax. But as you mentioned, you're aware of the security risks.

The best method is always to work with SSH keys, whether for fun or production.

• GitHub error - Key is invalid. You must supply a key in OpenSSH public key format