give_me_hostname

#!/bin/bash
#
# Copyright (C) 2015 barbUk
#
# This program is free software: you can redistribute it and/or modify it under
# the terms of the GNU General Public License as published by the Free Software
# Foundation, either version 3 of the License, or (at your option) any later
# version.
#
# This program is distributed in the hope that it will be useful, but WITHOUT
# ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS
# FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details.
#
# You should have received a copy of the GNU General Public License along with
# this program. If not, see <http://www.gnu.org/licenses/>.
#

set -o errexit -o pipefail -o nounset

readonly mode="${1:-}"

awk_command=awk
if [ "$(uname)" = "Darwin" ]; then
    awk_command=gawk
fi

dsh_hosts() {
    local file
    file="$HOME/.dsh/group/all"
    if [ -f "$file" ]; then
        grep -vE '^#' "$file"
    fi
}

known_hosts() {
    local file
    file="$HOME/.ssh/known_hosts"
    if [ -f "$file" ]; then
        "$awk_command" '{print $1}' "$file"    \
            | grep -v ^\|           \
            | cut -d, -f 1          \
            | sed -e 's/\[//g'      \
            | sed -e 's/\]//g'      \
            | cut -d: -f1           \
            | grep -v ssh-rsa
    fi
}

bash_history() {
    local file
    file="$HOME/.bash_history"
    if [ -f "$file" ]; then
        grep -E "^host|^dig|^drill|^ping|^whois" "$file" \
            | "$awk_command" '{print $NF}'
    fi
}

ssh_config() {
    local file
    file="$HOME/.ssh/config"
    if [ -d "$(dirname "$file")" ]; then
        "$awk_command" '/^Host/ && ! /\*/ {print $2}' "$file"
    fi
}

ssh_config_d() {
    local file
    file="$HOME/.ssh/config.d/*"
    if [ -d "$(dirname "$file")" ]; then
        # shellcheck disable=2086
        "$awk_command" '/^Host/ && ! /*/ {print $2}' $file
    fi
}

main() {
    case "$mode" in
        "dsh") dsh_hosts | sort -u;;
        "hosts") known_hosts | sort -u;;
        "ssh")
            (
                ssh_config_d
                dsh_hosts
                known_hosts
            ) | grep -vE "\\b([0-9]{1,3}\\.){3}[0-9]{1,3}\\b" | sort -u
        ;;
        "ips")
            (
                bash_history
                known_hosts
            ) | grep -oE "\\b([0-9]{1,3}\\.){3}[0-9]{1,3}\\b" | sort -u
        ;;
        "all")
            (
                dsh_hosts
                ssh_config_d
                known_hosts
                bash_history
            ) | sort -u
        ;;
        *)
            (
                dsh_hosts
                known_hosts
                bash_history
            ) | grep -vE "\\b([0-9]{1,3}\\.){3}[0-9]{1,3}\\b|^@|^\\+|^\\.'" | sort -u
        ;;
    esac

    return 0
}
main