DNS Resolver Information Script

Overview

This script enhances common terminal commands like curl and ping by displaying the DNS resolver used to resolve the hostname. It checks whether the hostname was resolved using:

1. /etc/hosts
2. A specific DNS server

Key Features

• Automatically detects if /etc/hosts was used for resolution.
• Queries configured DNS servers to determine which was used.
• Works seamlessly as a wrapper for curl and ping commands.

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Setup

Prerequisites

• macOS or a Unix-like operating system with the following tools installed:
  • scutil (default on macOS)
  • dig
  • awk

Installation

1. Copy the script into your shell configuration file (e.g., ~/.zshrc or ~/.bashrc).

   resolve_source() {
       local hostname="$1"
   
       # Check if the hostname is in /etc/hosts
       if grep -q "$hostname" /etc/hosts; then
           echo "Resolved using /etc/hosts"
           return
       fi
   
       # Use scutil to determine DNS server and query resolution
       local dns_servers
       dns_servers=$(scutil --dns | grep "nameserver\[[0-9]*\]" | awk '{print $3}')
   
       # Use dig to query the hostname
       for server in $dns_servers; do
           if dig @"$server" +short "$hostname" > /dev/null 2>&1; then
               echo "Resolved using DNS server: $server"
               return
           fi
       done
   
       echo "Resolver source unknown"
   }
   
   resolver_info() {
       local hostname="$1"
       resolve_source "$hostname"
   
       # Run the actual command
       shift
       "$@"
   }
   
   curl_resolver() {
       local host="$(echo "$1" | sed 's|http[s]*://||' | cut -d/ -f1)"
       resolver_info "$host" curl "$@"
   }
   
   ping_resolver() {
       resolver_info "$1" ping "$@"
   }
   
   alias curlr="curl_resolver"
   alias pingr="ping_resolver"

2. Save the file.

3. Reload your shell configuration:

   source ~/.zshrc  # or ~/.bashrc depending on your shell

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Usage

Wrapped Commands

The script provides the following aliases:

• curlr: Enhanced curl command with resolver information.
• pingr: Enhanced ping command with resolver information.

Examples

Curl Example:

curlr http://google.com

Output:

Resolved using DNS server: 8.8.8.8
[Standard curl output]

curlr http://domaininmyhostfile.com

Output:

Resolved using /etc/hosts
[Standard curl output]

Ping Example:

pingr google.com

Output:

Resolved using DNS server: 8.8.8.8
PING google.com (127.0.0.1): 56 data bytes
[Standard ping output]

pingr http://domaininmyhostfile.com

Output:

Resolved using /etc/hosts
[Standard ping output]

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Notes

1. The script uses scutil --dns to retrieve DNS server information on macOS. On other systems, you may need to replace this with an equivalent command (e.g., systemd-resolve --status or resolvectl).
2. Ensure dig is installed and available in your PATH. On macOS, you can install it via Homebrew:

   brew install bind

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Customization

Feel free to modify the aliases or add new functions for other commands that involve hostname resolution. For example, you could extend it to wget or ssh.

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Troubleshooting

• DNS resolution issues: Ensure your system's DNS settings are configured correctly.
• dig not found: Install dig using your system's package manager (e.g., Homebrew, apt, or yum).

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License

This script is open source and provided "as is" without warranty. Feel free to modify and distribute it under the MIT License.