SSHazam!

This tool speculatively opens SSH ControlMaster connections when you use bash autocomplete to fill in a server name. It saves you <duration> of annoyance every day!

How it Works

When you type in an ssh command and auto-complete the server name, it examines your ~/.ssh/config file and suggests completions. If only a few suggestions are presented, it opens a ControlMaster connection to these servers in the background; when you eventually select the correct server ssh automatically uses the ControlMaster connection, saving you precious <duration>,

It supports these types of commands to connect to server yggdrasil:

ssh yg<tab>
ssh freyr@yg<tab>
ssh -o Option=Value ... yg<tab>
ssh -o Option=Value ... freyr@yg<tab>

It does not support changing verbosity for connection debugging: ssh -v, ssh -vvv, etc. (ControlMaster client connections have the same verbosity as the master connection.)

Requirements

This requires a reasonably modern version of bash. We recommend BASH 4.4.18 or later; this corresponds to the default shell on Ubuntu 16.04 and later. However, the default BASH 3.2 on OS X will usually work.

For OS X, the following steps must first be executed. (For Ubuntu, these are unnecessary.):

Optional: Upgrade bash version via instructions here.
Install flock via instructions here.
Install coreutils via instructions here.

Usage

To use this utility once, download the script and run source ssh_autocomp.bash. To install it, save it somewhere and add the source line to your ~/.bashrc or ~/.bash_profile or similar.

Configuration information is stored in the head of the file itself. You can set the following variables:

SSH_CONFIG_PATHS: a space-separated list of paths to search for HOST directives.
MAX_CM_OPEN: the maximum number of ControlMaster connections to open; if there are more than these many possible servers in your auto-complete then use a heuristic to decide which connections to open.
HEURISTIC: the heuristic to use to decide which connections to open; values are "", "last", "most"
HEURISTIC_CACHE_LNC: cache file for last heuristic
HEURISTIC_CACHE_MC: cache file for most heuristic

Remember to run source ssh_autocomp.bash each time you change the file!

Heuristics

"": If a blank heuristic is specified no automatic connections are made.
"last": Open the $MAX_CM_OPEN servers most recently connected to; this heuristic updates its list of recently-connected servers every day or whenever any file in SSH_CONFIG_PATHS is updated.
"most": Open the $MAX_CM_OPEN servers most often connected to; this heuristic updates its list of recently-connected servers every day or whenever any file in SSH_CONFIG_PATHS is updated.

Debugging