Synopsis:
   $twiddle(<tilde-expansion>)

Technical:
   This function is used to do tilde-expansion on the given name.  The tilde
   is required.  If a user exists on the system with a home directory, the
   full path of that directory is returned.  If the user does not exist,
   nothing is returned.  If a tilde is not the first character, the input is
   returned.

Practical:
   This is useful for ensuring that files will be written to your home
   directory, regardless of the current directory.

Returns:
   full path of home directory if user exists, nothing if not, input if error

Examples:
   $twiddle(~)                  returns your home directory
   $twiddle(~jvs)               returns home directory for user jvs
   $twiddle(~nosuchuser)        no such user, returns nothing
   $twiddle(blah)               bad input, returns "blah"

See Also:
   Environment(7); cd(4)