Amen to cfajohnson, he is absolutely correct. Still, there are some additional points to a script creating users I'd like to stress:

1) Your script has several prerequisites which should be tested. You test for the script being run as as root and quite correctly so. Still there should be tested a lot of more conditions: is your file readable, is it in the expected format (how does your script behave if a line looks "user @host" instead of "user@host"? What will happen if the host specified doesn't exist?), etc.. Robust scripting always takes into account the probable typo and other typical errors.

1a) Corollary: most of these tests are very generic and could be done in (external) functions, for instance the test if it is run under root privileges. Presumably you have a lot of other scripts also depending on being run under root. Why don't you write a function "Being_Root()", which just tests this condition and gives back TRUE or FALSE. Accordingly with some other necessary prerequisites.

2) In your script no effort is undertaken to find (and correct) error conditions. Suppose you let your script run and one of the user accounts does already exist. How does your script react in this case? Terminate? Write a log entry? Issue an error message on the screen? How should your script deal with such a problem?

3) Your script gives back no return value. This way it will not be possible to include it into future scripts, because you don't get back any information if the run was successful or not. Well-behaved programs return an error code upon termination (usually: 0=ok, 1-255 several error conditions, like: input file missing, prerequisites not met, user already existing, ... )

I hope this helps.

bakunin