What does __FILE__ mean?

Question

I have the following code from Codeigniter index.php

My understanding is that,

If / of string position in $system_folder

Answer 1

__FILE__

The full path and filename of the file. If used inside an include, the name of the included file is returned. Since PHP 4.0.2, FILE always contains an absolute path with symlinks resolved whereas in older versions it contained relative path under some circumstances.

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string dirname  ( string $path  )

Given a string containing a path to a file, this function will return the name of the directory.

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str_replace("\\", "/", $system_folder)

You need this to be consisten in path separators between different operating systems. Windows uses \ and *nix uses /, you keep with /.