Pass a password to ssh in pure bash
I want to pass a password to ssh using a bash script (Yes, I know that there are ssh keys that I could use, but this is not what I intend).
I found some solutions that were using expect but since it is not a standard bash tool I am wondering if I can do this using pipes.
Can someone explain to me, why exactly something like this:
echo "password\n" | ssh somehost.com
or
ssh somehost.com <(echo "password\n")
doesn't work? Is there any possibility to make it work? Maybe executing ssh as a different process, obtaining its PID and then sending a string directly to it?
You can not specify the password from the command line but you can do either using ssh keys or using sshpass as suggested by John C. or using a expect script.
To use sshpass, you need to install it first. Then
sshpass -f <(printf '%s\n' your_password) ssh user@hostname
instead of using sshpass -p your_password. As mentioned by Charles Duffy in the comments, it is safer to supply the password from a file or from a variable instead of from command line.
BTW, a little explanation for the <(command) syntax. The shell executes the command inside the parentheses and replaces the whole thing with a file descriptor, which is connected to the command's stdout. You can find more from this answer https://unix.stackexchange.com/questions/156084/why-does-process-substitution-result-in-a-file-called-dev-fd-63-which-is-a-pipe
Since there were no exact answers to my question, I made some investigation why my code doesn't work when there are other solutions that works, and decided to post what I found to complete the subject.
As it turns out:
"ssh uses direct TTY access to make sure that the password is indeed issued by an interactive keyboard user." sshpass manpage
which answers the question, why the pipes don't work in this case. The obvious solution was to create conditions so that ssh "thought" that it is run in the regular terminal and since it may be accomplished by simple posix functions, it is beyond what simple bash offers.