from the man page of su:
EXAMPLES
Example 1: Becoming User bin While Retaining Your Previously
Exported Environment

To become user bin while retaining your previously exported
environment, execute:

example% su bin

Example 2: Becoming User bin and Changing to bin's Login
Environment

To become user bin but change the environment to what would
be expected if bin had originally logged in, execute:

example% su - bin

Found the info for my orig ques "what's the diff btwn su and su - when switching to root?"

I just don't understand it. Can anyone explain with an example of when to use su or su - when switching to root?

I have always just done "su" and I always see evryone else using "su -" when switching to root. ??

If you login as root on console, you get root's environment set up - which may include more paths to commands/libraries/whatever.

If you su - root, it would be the same as logging in as root.

If you su root, you are only getting the priviledges of root, but the environment is yours, which may not include the correct paths to do some commands.

This is one example!

Any reasons for not just always using "su -"? Just one extra key. Why would you even bother using "su"?

If you want to inherit the current shell we have to use su with out - ;
You will have subshell having all the previous environment.

When you do su - userid .., you will lose the current shell. it is equivalent to rlogin command. You will lose current shell environement.

See the following example.

$ export var1="hello"
$ echo $var1
hello
$ su user1
user1's Password:
$ echo $var1
hello
------------------> see var1 is retained to the new sub shell.
$ export var2="world"
$ su - user1
user1's Password:

$echo $var2

$

------------------> see var2 is NOT retained to the new shell.

Thanks - that really help's. Make sense now.

Thanks for the example.