$ sudo apt-get install sshpass
$ sshpass -p your_password ssh user@hostname

Don't use a password. Generate a passphrase-less SSH key and push it to your VM.

If you already have an SSH key, you can skip this step… Just hit Enter for the key and both passphrases:

$ ssh-keygen -t rsa -b 2048
Generating public/private rsa key pair.
Enter file in which to save the key (/home/username/.ssh/id_rsa):
Enter passphrase (empty for no passphrase):
Enter same passphrase again:
Your identification has been saved in /home/username/.ssh/id_rsa.
Your public key has been saved in /home/username/.ssh/id_rsa.pub.

Copy your keys to the target server:

$ ssh-copy-id id@server
id@server's password:

Now try logging into the machine, with ssh 'id@server', and check-in:

.ssh/authorized_keys

Note: If you don't have .ssh dir and authorized_keys file, you need to create it first

to make sure we haven’t added extra keys that you weren’t expecting.

Finally, check to log in…

$ ssh id@server

id@server:~$

You may also want to look into using ssh-agent if you want to try keeping your keys protected with a passphrase.

While the correct answer for your question is sshpass (see other answer for details), there is a more secure way - SSH keys. You are just three easy steps away from the solution:

All the following commands are being run on the client side, i.e. your machine

Enter the following command to start generating a rsa keypair:

# ssh-keygen

When the message 'Enter file in which to save the key' appears, just leave the filename blank by pressing Enter.

When the terminal asks you to enter a passphrase, just leave this blank (Warning: read below) too and press Enter.

Then copy the keypair onto the server with one simple command:

# ssh-copy-id userid@hostname

you can now log in without a password:

# ssh userid@hostname

WARNING: Leaving SSH keys exposed without encrypting them is a not good practice even if you encrypt your whole drive. What is much safer is to actually enter a passphrase when generating keys and then use Keychain (MacOS, Linux) or SSH agent to remember the passphrase until you signout or suspend or timeout, depending on what you prefer.

Use expect:

#!/usr/bin/expect -f
#  ./ssh.exp password 192.168.1.11 id
set pass [lrange $argv 0 0]
set server [lrange $argv 1 1]
set name [lrange $argv 2 2]

spawn ssh $name@$server
match_max 100000
expect "*?assword:*"
send -- "$pass\r"
send -- "\r"
interact

Example:

# ./1.ex password localhost ooshro
spawn ssh ooshro@localhost
ooshro@localhost's password: 
Linux ubuntu-1010-server-01 2.6.35-25-generic-pae #44-Ubuntu SMP Fri Jan 21 19:01:46 UTC 2011 i686 GNU/Linux
Ubuntu 10.10

Welcome to Ubuntu!
 * Documentation:  https://help.ubuntu.com/
Last login: Tue Mar  1 12:41:12 2011 from localhost

SSH single sign-on is usually achieved with public key authentication and an authentication agent. You could easily add your test VM key to an existing auth agent (see example below). Other methods such as gssapi/kerberos exist but are more complex.

sshpass

In situations where password is the only authentication method available, sshpass can be used to automatically enter the password. Please pay particular attention to the SECURITY CONSIDERATIONS section of the man page. In all three options, the password is visible or stored in plaintext at some point:

Anonymous pipe (recommended by sshpass)

# Create a pipe
PIPE=$(mktemp -u)
mkfifo -m 600 $PIPE
# Attach it to file descriptior 3
exec 3<>$PIPE
# Delete the directory entry
rm $PIPE
# Write your password in the pipe
 echo 'my_secret_password' >&3
# Connect with sshpass -d
sshpass -d3 ssh user@host

# Close the pipe when done
exec 3>&-

It is quite cumbersome in bash, arguably easier with programming languages. Another process could attach to your pipe/fd before the password is written. The window of opportunity is quite short and limited to your processes or root.

Environment variable

# Set your password in an environment variable
 export SSHPASS='my_secret_password'
# Connect with sshpass -e
sshpass -e ssh user@host

You and root can read your process' environment variables (i.e. your password) while sshpass is running (cat /proc/<pid>/environ | tr '\0' '\n' | grep ^SSHPASS=). The window of opportunity is much longer but still limited to your own processes or root, not other users.

Command-line argument (least secure)

 sshpass -p my_secret_password ssh user@host

This is convenient but less secure as described in the man page. Command line arguments are visible to all users (e.g. ps -ef | grep sshpass). sshpass attempts to hide the argument, but there is still a window during which all users can see your password passed by argument.

Side note

Set your bash HISTCONTROL variable to ignorespace or ignoreboth and prefix your sensitive commands with a space. They won't be saved in history.

SSH public key authentication

# Generate a key pair
# Do NOT leave the passphrase empty
ssh-keygen
# Copy it to the remote host (added to .ssh/authorized_keys)
ssh-copy-id user@host

The passphrase is very important. Anyone somehow obtaining the private key file won't be able to use it without the passphrase.

Setup the SSH authentication agent

# Start the agent
eval `ssh-agent`
# Add the identity (private key) to the agent
ssh-add /path/to/private-key
# Enter key passphrase (one time only, while the agent is running)

Connect as usual

ssh user@host

The advantage is that your private key is encrypted and you only need to enter its passphrase once (via a safer input method too).

I am surprised nobody mentioned plink from the putty-tools package in Ubuntu:

plink user@domain -pw mypass  [cmd]

It also available on Windows and the syntax is mostly compatible with the openssh client.

This might not be any use to you, but you can do it with Perl:

\#!/usr/bin/perl  
use warnings;  
use strict;  

use Net::SSH::Perl;  
my $host = 'remote.serv.er';  
my $user = 'root';  
my $pass = 'hunter2';  
my $ssh = Net::SSH::Perl->new('$host');  
$ssh->login('$user', '$pass') or die "Oh noes! $!";

I prefer passh https://github.com/clarkwang/passh

sshpass is broken by design.

when the ssh server is not added already in my known_hosts, sshpass will not show me the message to add the server to my known hosts, passh do not have this problem.

Login to a remote server:

$ passh -p password ssh user@host

Sure you don't want to use SSH keys rather than passwords? That way it's both secure and automatic.

Depending on your automation needs, perhaps Ansible would be a good fit for you. It can nicely manage things like prompting for password, prompting for sudo password, various ways of changing use, securely using encrypted secrets (vault).

If that’s not suitable, I would suggest Expect, as suggested in another answer.