[tlug] sed / shell / redirection question

[Mark Makdad <mark@example.com>]

TLUG,

I would like to write a bash script to automate the update of some 
scripts I have.  I made the mistake of hard-coding the pathname into 
some of them (before I wised up and used a variable), and I don't want 
to go through 100+ php files and update them manually.

I constructed the following sed statement:

sed 's*old/path/name*new_variable_name*' ....

But then I decided to make this into a shell script, so:

#!/bin/bash
for X in *.php
do
   sed 's*old/path/name*new_variable_name*' $X > $X
done

Which seemed to work?  I'm not sure, I tried many things, and when I 
executed sed by itself on the shell I got the desired results.  However, 
I don't want to rename the files a bunch of times; I want to edit them 
as-is.  My question is:

Why did this take all of my input files and truncate them at zero bytes?

Am I screwing up a basic redirection thing there?  And also, does anyone 
have a stiff drink?   I just overwrote 20 files and just lost about an 
hour of work (yay backups).  My mistake, though, for playing with fire 
without backing up.

Cheers,

Mark