Finding nonprintable characters?

[VanL]

Hello,

I have a function

isBinary(filehandle)

that I'm not sure how to implement.  I've decided to define binary as 
containing characters above \x80.  But  what is the best way to do this?

1. iterate through xreadline, so the whole thing doesn't get loaded into 
memory?

2. String searching?  If so, for what string?  Searching for anything 
greater  than \x7f?

3. Re searching?  for what class?


Thanks in advance,

Van