Simple bash completion for ssh

#
# Add to ~/.bash_profile or put in /etc/bash_completion.d/ssh
# NB: May not be as "complete" as, say, /usr/share/bash-completion/completions/ssh,
#     but at least it hits all the files I need and only uses a single awk to do it
#     (a lot of other implementations are far less efficient or overly complicated).
# NB: Supports known_hosts(5) and ssh_config(5) formats based on filename
#
_ssh()
{
    local file files=
    for file in \
        ~/.ssh/config ~/.ssh/config.d/* \
        ~/.ssh/known_hosts /etc/ssh/known_hosts \
    ; do [ -e "$file" ] && files="$files $file"; done
    [ ! "$files" ] || COMPREPLY=( $( compgen -W "$( awk '
        FILENAME ~ /config/ && tolower($1) == "host" {
            for (n = 2; n <= NF; n++) if ($n !~ /[?*]/) print $n
        }
        FILENAME ~ /hosts/ {
            for (n = split($1, hosts, /,/); n > 0; n--) {
                if ((len = length(hosts[n])) < 1) continue
                if ((host = hosts[n]) ~ /^\[.*\]$/)
                    host = substr(host, 2, len - 2)
                print host
            }
        }
    ' $files 2> /dev/null )" -- ${COMP_WORDS[COMP_CWORD]} ) ) || : ok
}
complete -F _ssh ssh