If you are not appending to the end of the file then you are overwriting. That's how files work. There is no way to insert at the beginning or in the middle of a file.

If you want to prepend your records then
a) load the entire file into memory, prepend, and write it all back out, or
b) write the new record to a temporary file, append the old file into it, and rename the new file onto the old one

"There is no way to insert at the beginning or in the middle of a file." That statement appears to be incorrect.

https://www.php.net/manual/en/function.fseek.php

Sets the file position indicator for the file referenced by handle. The new position, measured in bytes from the beginning of the file, is obtained by adding offset to the position specified by whence.

The coding that I submitted does insert in the middle of the file. The "bug" I'm reporting inserts white space in addition to the output which is what I want to delete.

You cannot *insert* into the file. You can *overwrite*.

Open up your favorite text editor. Pull open any file you like and put the cursor somewhere in the middle. Then turn on your editor's overwrite/overtype mode (probably Ins key) and start typing. That's what fseek-ing into the middle and fwrite-ing will do, except it will overwrite newlines as well.

Please tell me something I don't know. I want insert and no overwrite.

fseek() determines the pointer position. fopen determines truncate or append and also pointer position. "fopen" appears to be the root of my problem, and not "fseek" as I first thought.

https://www.php.net/manual/en/function.fopen.php
'a' Open for writing only; place the file pointer at the end of the file. If the file does not exist, attempt to create it. In this mode, fseek() has no effect, writes are always appended.

Is it possible to have a mode similar to 'a' as follows?
Open for writing only; place the file pointer at the beginning of the file. If the file does not exist, attempt to create it. In this mode, fseek() to be effective, writes are always appended.

If I knew where to amend coding in PHP, I could probably fix this myself.

Inserting something into a file is a very expensive operation,
since everything that follows the insertion position would have to
be moved.  This is why this operation is not available; if you
need it, you have to move the existing contents yourself.

Please advise the path to "fopen" and "fwrite" and I'll attempt to fix the problem?

And if it works I'll share it as no doubt others will want to insert & no overwrite.

If it is an expensive operation to insert, then it will probably be less expensive to modify an existing mode such as "x" or "c", which would be more useful to the wider community.