Simple command that switches between two host files

Question

I am using /etc/host to map localhost to a web domain. I would like a fast way of doing this rather than searching and replacing every time. I put this in my .bashrc file.

alias hostchange='
nowdir=$PWD;
cd /etc;
mv hosts hoststempname;
mv hostssecondary hosts;
mv hoststempname hostssecondary;
cd $nowdir'

I am getting this error and it won't progress regardless y or n.

mv: rename hosts to hoststempname: Permission denied
override rw-r--r--  root/wheel for hosts? (y/n [n]) 

I got it to work by adding sudo.

alias hostchange='
nowdir=$PWD;
cd /etc;
sudo mv hosts hoststempname;
sudo mv hostssecondary hosts;
sudo mv hoststempname hostssecondary;
cd $nowdir'

Is this legitimate, I'm taking a shot in the dark here?

Answer 1

You are on the right track! A couple comments about this. It is usually better practice to leave multi-line actions like this to functions. I'd probably write it like this:

change_etc_hosts_file() {
  set -e # stop running if we encounter an error
  sudo \mv -f /etc/hosts /etc/hoststempname
  sudo \mv -f /etc/hostssecondary /etc/hosts
  sudo \mv -f /etc/hoststempname /etc/hostssecondary
  set +e
}
alias changehosts=change_etc_hosts_file

You'll notice I also used absolute paths instead of changing directory. This is usually a better idea (to use absolute paths). If you do want to keep using relatives then it is usually better to do that in a sub-shell so you don't have to handling changing directory back to $PWD (which if you abort will leave you in a weird state). To do it as a sub-shell it would look like this:

change_etc_hosts_file() {
  ( # use subshell
    cd /etc
    set -e # stop running if we encounter an error
    sudo \rm -f hoststempname # the \ escapes aliases which might cause prompting
    sudo \cp -f hosts hoststempname
    sudo \cp -f hostssecondary hosts
    sudo \cp -f hoststempname hostssecondary
  )
}

The cd happens inside the () which is a new process so it won't affect your current working directory.

Answer 2

_{The fact of you having doubts about the sudo command shows that somehow you survived so far in the Unix world without possessing the basic knowledge about the concept of unix users (root especially). Although this situation is incomprehensible to me, your question along with the comments clearly indicate that is the case.}

Yes, what you achieved with sudo is just what is expected. This is because:

• On Unix systems, there is a number of system users - you can call them 'virtual' (these are not to be mistaken with human computer users).
• Each file and directory has it's owner, which is always one of the (virtual) users.
• The root user, known as superuser is the special system account every Unix has to have. He can do everything - has full power over the system.
• sudo is a command used to temporarily leverage "normal" user's privileges to root so that some special tasks can be performed.

Do have a further read about root, sudo and file permissions on these example sites: 1, 2, 3, 4, 5, 6