Why can't I sudo some commands? (e.g., vim)

When running sudo, many systems are configured to clear the environment of all non-whitelisted values, and to reset the PATH variable to a sanitized value.

You will find the former as Defaults env_reset and several Defaults env_keep += "SOME_VARIABLE_NAME" in /etc/sudoers. The latter "secure" PATH override is specified as Defaults secure_path = /sbin:/bin:/usr/sbin:/usr/bin – delete this line to remove this behavior when sudoing.

How which environment variable is handled is printed when you run sudo -V as root.

If you don't want to get rid of these defaults, you can always specify programs using their full path (sudo /usr/local/bin/vim).

Alternatively, you can allow your account to SETENV in the sudoers file, for example:

%wheel  ALL=(ALL)       SETENV: ALL

This allows you to override environment defaults like this: sudo PATH=$PATH which vim, as the variable is intepreted by your shell before the command is executed, resulting in an inherited PATH (which will likely not include /sbin etc. though).

sudo echo $PATH

does not do what you think. $PATH gets replaced by the (your) shell before execuitng the command.

To accomplish the desired behavior, you can use sudo -i.

From man sudo:

-i [command]

The -i (simulate initial login) option runs the shell specified in the passwd(5) entry of the target user as a login shell. This means that login-specific resource files such as .profile or .login will be read by the shell. If a command is specified, it is passed to the shell for execution.

How do I get sudo <command> to work?

Until you resolve the problem with paths use a full pathname

  sudo /usr/local/bin/vim /var/www/html/index.html