Adds a hostname to a given IP address in /etc/hosts.

add_hostname_to_etc_hosts.sh

#!/usr/bin/env bash

# The MIT License (MIT)
# 
# Copyright (c) 2023 Christian Haintz
# 
# Permission is hereby granted, free of charge, to any person obtaining a copy of
# this software and associated documentation files (the "Software"), to deal in
# the Software without restriction, including without limitation the rights to
# use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of
# the Software, and to permit persons to whom the Software is furnished to do so,
# subject to the following conditions:
# 
# The above copyright notice and this permission notice shall be included in all
# copies or substantial portions of the Software.
# 
# THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
# IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS
# FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR
# COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER
# IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN
# CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.


###############################################################
# Adds a hostname to a given IP address.                      #
# Doesn't add a new line if IP is already present             #
#                                                             #
# Usage: add_hostname_to_hosts.sh <ip_address> <hostname>     #
###############################################################

# Check if the script is run with root privileges
if [ "$(id -u)" -ne 0 ]; then
    echo "This script must be run as root or with sudo."
    exit 1
fi

# Check if the correct number of arguments is provided
if [ $# -ne 2 ]; then
    echo "Usage: $0 <IP_ADDRESS> <HOSTNAME>"
    exit 1
fi

IP_ADDRESS="$1"
HOSTNAME="$2"
HOSTS_FILE="/etc/hosts"

# Check if the IP address is already present in the hosts file
IP_EXISTS=$(grep -w "$IP_ADDRESS" "$HOSTS_FILE")

if [ -z "$IP_EXISTS" ]; then
    # Add the IP address and hostname to the hosts file
    echo "$IP_ADDRESS $HOSTNAME" >> "$HOSTS_FILE"
    echo "Added $IP_ADDRESS $HOSTNAME to $HOSTS_FILE."
else
    # Check if the hostname is already present for the IP address
    HOSTNAME_EXISTS=$(echo "$IP_EXISTS" | grep -w "$HOSTNAME")

    if [ -z "$HOSTNAME_EXISTS" ]; then
        # Add the hostname to the existing IP address entry
        TEMP_FILE=$(mktemp)
        sed "/$IP_ADDRESS/s/$/ $HOSTNAME/" "$HOSTS_FILE" > "$TEMP_FILE"
        cat "$TEMP_FILE" > "$HOSTS_FILE"
        rm "$TEMP_FILE"
        echo "Added $HOSTNAME to the existing IP address entry in $HOSTS_FILE."
    else
        echo "The hostname $HOSTNAME is already present for the IP address $IP_ADDRESS in $HOSTS_FILE."
    fi
fi