no it doesn't:
open to write (will overwrite the file)
int $fileid = `fopen $filename "w"`;
open to append to the file
int $fileid = `fopen $filename "a"`;
//from the docs
"w" open file for writing (destroys prior contents of file).
"a" append for writing (appends to end of file).
"r" open for reading.
Technical Director - Framestore
Currently working on: Your Highness