What exactly is PATH_INFO in PHP?

Solution 1:

Actually, PATH_INFO is related to the Apache Web Server serving PHP pages and not PHP per se.

PATH_INFO is an environment variable set by Apache when the AcceptPathInfo directive is turned on. It will contain trailing pathname information that follows an actual filename or non-existent file in an existing directory, whether the request is accepted or rejected. Environment variables are then passed on to the Apache/CGI module in charge of rendering the page.

The variable is accessible in PHP using $_SERVER['PATH_INFO'].

For example, assume the location /test/ points to a directory that contains only the single file here.html. Then requests for /test/here.html/more and /test/nothere.html/more both collect /more as PATH_INFO.

Apache Core Documentation: AcceptPathInfo Directive

Solution 2:

As the variable PATH_INFO is part of the definition for CGI you should also take a look in there ;)

The PATH_INFO variable specifies a path to be interpreted by the CGI script. It identifies the resource or sub-resource to be returned by the CGI script, and is derived from the portion of the URI path hierarchy following the part that identifies the script itself. Unlike a URI path, the PATH_INFO is not URL-encoded, and cannot contain path-segment parameters. A PATH_INFO of "/" represents a single void path segment.

 PATH_INFO = "" | ( "/" path )
 path      = lsegment *( "/" lsegment )
 lsegment  = *lchar
 lchar     = <any TEXT or CTL except "/">

https://www.rfc-editor.org/rfc/rfc3875#section-4.1.5