This a very simple script that will comment host names depending on their initial numbering. My home network setup is different than my home's, and therefore I use this script to change the hostnames I use for development testing purposes.

change_hosts.sh

#!/bin/sh

if [ "$1" != "work" ] && [ "$1" != "home" ];
then
    echo "Wrong arguments Usage: $0 home|work"
    exit 65
fi

work_test_regex="^10"
home_test_regex="^192"
work_off_regex="/^10/#10/g"
work_on_regex="/^#10/10/g"
home_off_regex="/^192/#192/g"
home_on_regex="/^#192/192/g"

if [ "$1" == "work" ];
then
    
    work_test=`grep $work_test_regex /etc/hosts`

    if [ -z "$work_test" ]; 
    then
        sed -i.bak "s$work_on_regex" /etc/hosts
        sed -i.bak "s$home_off_regex" /etc/hosts
    else 
        echo "Aborting switch to work mode since work mode seems to be activated."
        exit 1   
    fi
else

    home_test=`grep $home_test_regex /etc/hosts`

    if [ -z "$home_test" ]; 
    then
        sed -i.bak "s$home_on_regex" /etc/hosts
        sed -i.bak "s$work_off_regex" /etc/hosts
    else 
        echo "Aborting switch to home mode since home mode seems to be activated."
        exit 1
    fi
fi

Since `$work_test isn't used, it might be easier to read with just:

if ! grep -q $work_test_regex /etc/hosts;
then

A cleaner way to use if with exit status, just a small suggestion.