fish-shell/share/functions/__fish_print_hostnames.fish

function __fish_print_hostnames -d "Print a list of known hostnames"
    # Print all hosts from /etc/hosts
    # use 'getent hosts' on OSes that support it (OpenBSD and Cygwin do not)
    if type -q getent; and getent hosts >/dev/null 2>&1 # test if 'getent hosts' works and redirect output so errors don't print
        # Ignore zero ips
        getent hosts | string match --regex --invert '^0.0.0.0' \
            # Remove left addresses column
            | string replace --regex '^\s*\S+\s+' '' \
            # Tokenize remaining hostnames and aliases columnss
            | string split ' '
    else if test -r /etc/hosts
        # Ignore commented lines and functionally empty lines
        string match --regex --invert '^\s*0.0.0.0|^\s*#|^\s*$' </etc/hosts \
            # Strip comments
            | string replace --regex --all '#.*$' '' \
            # Remove left addresses column
            | string replace --regex '^\s*\S+\s+' '' \
            # Tokenize remaining hostnames and aliases columns
            | string trim | string replace --regex --all '\s+' ' ' | string split ' '
    end

    # Print nfs servers from /etc/fstab
    if test -r /etc/fstab
        string match -r '^\s*[0-9]{1,3}\.[0-9]{1,3}\.[0-9]{1,3]:|^[a-zA-Z\.]*:' </etc/fstab | string replace -r ':.*' ''
    end

    # Check hosts known to ssh
    set -l known_hosts ~/.ssh/known_hosts{,2} /etc/ssh/known_hosts{,2} # Yes, seriously - the default specifies both with and without "2"
    # Check default ssh configs
    set -l ssh_config
    # Get alias and commandline options
    set -l ssh_command (functions ssh | string split ' ') (commandline -cpo)
    # Extract ssh config path from last -F short option
    if contains -- '-F' $ssh_command
        set -l ssh_config_path_is_next 1
        for token in $ssh_command
            if contains -- '-F' $token
                set ssh_config_path_is_next 0
            else if test $ssh_config_path_is_next -eq 0
                set ssh_config (eval "echo $token")
                set ssh_config_path_is_next 1
            end
        end
    else
        set ssh_config $ssh_config ~/.ssh/config
    end

    # Extract ssh config paths from Include option
    function _ssh_include --argument-names ssh_config
        # Relative paths in Include directive use /etc/ssh or ~/.ssh depending on
        # system or user level config. -F will not override this behaviour
        if test $ssh_config = '/etc/ssh/ssh_config'
            set relative_path '/etc/ssh'
        else
            set relative_path $HOME/.ssh
        end

        function _recursive --no-scope-shadowing
            set paths
            for config in $argv
                set paths $paths (cat $config ^/dev/null \
                # Keep only Include lines
                | string match --regex --ignore-case '^\s*Include\s+.+' \
                # Remove Include syntax
                | string replace --regex --ignore-case '^\s*Include\s+' '' \
                # Normalize whitespace
                | string trim | string replace --regex --all '\s+' ' ')
            end
            if test -n "$paths"
                # Expand paths which may have globbing and tokenize
                set paths (eval "echo $paths" | string split ' ')
                for path_index in (seq (count $paths))
                    # Resolve relative paths
                    if string match --invert '/*' $paths[$path_index] >/dev/null
                        set paths[$path_index] $relative_path/$paths[$path_index]
                    end
                    echo $paths[$path_index]
                end
                _recursive $paths
            end
        end
        _recursive $ssh_config
    end
    set -l ssh_configs (_ssh_include /etc/ssh/ssh_config) (_ssh_include $ssh_config)

    for file in $ssh_configs
        if test -r $file
            # Print hosts from system wide ssh configuration file
            string match --regex --ignore-case '^\s*Host\s+\S+' <$file \
                # We only want the value(s)
                | string replace --regex --ignore-case '^\s*Host\s+' '' \
                # Print one per line
                | string trim | string replace --regex '\s+' ' ' | string split ' ' \
                # Ignore hosts with a glob
                | string match --invert '*\**'
            # Extract known_host paths
            set known_hosts $known_hosts (string match -ri '^\s*UserKnownHostsFile|^\s*GlobalKnownHostsFile' <$file \
                | string replace -ri '.*KnownHostsFile\s*' '')
        end
    end
    for file in $known_hosts
        # Ignore hosts that are hashed, commented or have custom ports (like [localhost]:2200)
        test -r $file
        and string replace -ra '(\S+) .*' '$1' <$file | string match -r '^[^#|[=]+$' | string split ","
    end
    return 0
end