Well, the *RIGHT* answer is to stop using text files! That might have been an okay answer when you had a handful of members, but once you got to even 100 or so it was past time to start using a database.
And that means writing server-side code: PHP or ASP or JSP.
If I found you were doing this, I might be tempted to sue you for breach of privacy.
An optimist sees the glass as half full.
A pessimist sees the glass as half empty.
A realist drinks it no matter how much there is.