sshd_configure.bash

#!/bin/bash

# Set bash execution flags:
# - Treat unset variables as an error when substituting
# - Exit immediately if a command exits with a non-zero status
# - Print each command to stdout before executing it (useful for debugging)
set -u
# set -e
# set -x

# ANSI Colors
RED='\033[0;31m' # Error
GREEN='\033[0;32m' # Success
BLUE='\033[0;34m' # Info
YELLOW='\033[0;93m' # Warning/Useful info
NC='\033[0m' # No Color

# Usage example: show_usage
show_usage() {
    echo "= = Usage = ="
    echo "    Directly in CLI:"
    echo "        $0 [setting_name] [value]"
    echo "        Examples:"
    echo "            $0 Port 2222"
    echo "            $0 PermitRootLogin no"
    echo "            $0 PasswordAuthentication no"
    echo "    From WEB:"
    echo "        To run the script from the internet use:"
    echo "        curl:"
    echo "            curl -Ls https://raw.githubusercontent.com/voiduin/linux-host-setup/main/sshd_configure.bash | sudo bash -s [setting_name] [value]"
    echo "        wget:"
    echo "            wget -qO - https://raw.githubusercontent.com/voiduin/linux-host-setup/main/sshd_configure.bash | sudo bash -s [setting_name] [value]"
    echo -e "\n"
    echo "Requirements:"
    echo "    - Run as root"
    echo "Supported settings:"
    echo "    - Port, PermitRootLogin, PasswordAuthentication, and other valid sshd settings"
    echo "Config file requirements:"
    echo "    - The file must contain one active or commented 'Port' line"
    echo -e "\n"
    echo "Script created by \"Voiduin\""
    echo "Source available at https://github.com/voiduin/linux-host-setup"
}

# Exit with an error message and show usage
# Usage example: exit_with_err "Error message"
exit_with_err() {
    local message="$1"
    echo -e "${RED}Error: $message${NC}"
    echo -e "\n"
    show_usage
    exit 1
}

# Usage example: assert_run_as_root
assert_run_as_root() {
    if [[ $EUID -ne 0 ]]; then
        exit_with_err "This script must be run as root"
    fi
}

# Usage example: assert_file_exists "/path/to/file"
assert_file_exists() {
    local file_path="$1"
    if [[ ! -f "$file_path" ]]; then
        exit_with_err "The specified file does not exist: $file_path"
    fi
}

# Check SSHD configuration for a specified setting
#   check_sshd_config_setting <!config_file!> <!setting_name!>
# Usage example:
#   check_sshd_config_setting "/etc/ssh/sshd_config" "Port"
check_sshd_config_setting() {
    local config_file="$1"
    local setting_name="$2"

    # Find active setting lines and their line numbers.
    # This line must catch incorrect lines, e.g., lines with non-digit value:
    #     Port new_port # Changed by root on 2024-03-18, 12:24:41
    local setting_lines_info=$(grep -nE "^[[:blank:]]*${setting_name}[[:blank:]]" "${config_file}")

    # Count the number of active setting lines
    # Calculate active lines only if 'setting_lines_info' is not empty
    local active_lines
    if [[ -n "${setting_lines_info}" ]]; then
        active_lines=$(echo "${setting_lines_info}" | wc -l)
    else
        active_lines=0
    fi

    if [[ $active_lines -eq 1 ]]; then
        # OK
        local line_info=$(echo "$setting_lines_info" | awk -F ":" '{printf "%s\n%s\n", "    Line number " $1 ":", "    "$2}')
        echo "  - One active '$setting_name' line found in \"$config_file\":"
        echo "$line_info"
    elif [[ $active_lines -gt 1 ]]; then
        # ERR
        echo "  - Multiple active '$setting_name' lines found in \"$config_file\":"
        echo "$setting_lines_info" | awk -F ":" '{printf "%s\n%s\n", "    Line number " $1 ":", "        "$2}'
        exit_with_err "Multiple active '$setting_name' lines found. Please clean up the file."
    else
        echo "  - No active '$setting_name' line found in \"$config_file\""
        echo "    A new one will be added"
    fi
}

# Usage example: set_new_sshd_config "/etc/ssh/sshd_config" Port 2222
set_new_sshd_config() {
    local config_file="${1}"
    local setting="${2}"
    local value="${3}"

    local modifying_user="${SUDO_USER:-$(whoami)}"
    # Time delimiter set as "-" for easy AWK processing of "grep -n" output, which has the line number format "256:<string_value>"
    local modifying_time="$(date +'%Y-%m-%d, %H-%M-%S')"

    local original_line_val=$(grep -nE "^[[:blank:]]*${setting}[[:blank:]]" "${config_file}")
    local original_line_number=$(echo "$original_line_val" | cut -d':' -f1)
    # TODO: Return logic display previous value which set now
    # local original_port=$(echo "$original_line_val" | grep -Po '(?<=Port\s)\d+')

    local comment="# Changed by script on ${modifying_time} by user \"${modifying_user}\""

    if [[ ! -z "${original_line_number}" ]]; then
        sed -i "${original_line_number}s/.*/$setting $value ${comment}/" "$config_file"
        echo "    > ${setting} changed to $value on line ${original_line_number} in $config_file."
    else
        # Add new line in file end
        echo "${setting} ${value} ${comment}" >> "${config_file}"
        echo "    > ${setting} added with value \"${value}\" in \"${config_file}\""
    fi
}

main() {
    local config_file_path="/etc/ssh/sshd_config"
    local setting="$1"
    local value="$2"

    if [[ $# -gt 2 ]]; then
        exit_with_err "Too many arguments. Please provide only two arguments [name] [value]."
    fi

# TODO: Return check on port value
#     if ! [[ "$new_port" =~ ^[0-9]+$ ]] || [ "$new_port" -lt 1024 ] || [ "$new_port" -gt 65535 ]; then
#         exit_with_err "Invalid port number: $new_port. Please specify a number between 1024 and 65535."
#     fi

    if [[ -z "$setting" ]] || [[ -z "$value" ]]; then
        exit_with_err "ERR: Missing arguments. Please specify a setting and a value."
    fi

    assert_run_as_root
    assert_file_exists "${config_file_path}"
    check_sshd_config_setting "${config_file_path}" "${setting}"
    set_new_sshd_config "${config_file_path}" "${setting}" "$value"
}

main "$@"