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<title>PATH_INFO Changes in the CGI Environment</title>

<summary>

<p>As implemented in Apache 1.1.1 and earlier versions, the

method Apache used to create PATH_INFO in the CGI environment

was counterintuitive, and could result in crashes in certain

cases. In Apache 1.2 and beyond, this behavior has changed.

Although this results in some compatibility problems with

certain legacy CGI applications, the Apache 1.2 behavior is

still compatible with the CGI/1.1 specification, and CGI

scripts can be easily modified (<a href="#compat">see

below</a>).</p>

</summary>

<section id="prob"><title>The Problem</title>

<p>Apache 1.1.1 and earlier implemented the PATH_INFO and

SCRIPT_NAME environment variables by looking at the filename,

not the URL. While this resulted in the correct values in many

cases, when the filesystem path was overloaded to contain path

information, it could result in errant behavior. For example,

if the following appeared in a config file:</p>

<example>

Alias /cgi-ralph /usr/local/httpd/cgi-bin/user.cgi/ralph

</example>

<p>In this case, <code>user.cgi</code> is the CGI script, the

"/ralph" is information to be passed onto the CGI. If this

configuration was in place, and a request came for

"<code>/cgi-ralph/script/</code>", the code would set PATH_INFO

to "<code>/ralph/script</code>", and SCRIPT_NAME to

"<code>/cgi-</code>". Obviously, the latter is incorrect. In

certain cases, this could even cause the server to crash.</p>

</section>

<section id="solution"><title>The Solution</title>

<p>Apache 1.2 and later now determine SCRIPT_NAME and PATH_INFO

by looking directly at the URL, and determining how much of the

URL is client-modifiable, and setting PATH_INFO to it. To use

the above example, PATH_INFO would be set to

"<code>/script</code>", and SCRIPT_NAME to

"<code>/cgi-ralph</code>". This makes sense and results in no

server behavior problems. It also permits the script to be

guaranteed that

"<code>http://$SERVER_NAME:$SERVER_PORT$SCRIPT_NAME$PATH_INFO</code>"

will always be an accessible URL that points to the current

script, something which was not necessarily true with previous

versions of Apache.</p>

<p>However, the "<code>/ralph</code>" information from the

<code>Alias</code> directive is lost. This is unfortunate, but

we feel that using the filesystem to pass along this sort of

information is not a recommended method, and a script making

use of it "deserves" not to work. Apache 1.2b3 and later,

however, do provide <a href="#compat">a workaround.</a></p>

</section>

<section id="compat">

<title>Compatibility with Previous Servers</title>

<p>It may be necessary for a script that was designed for

earlier versions of Apache or other servers to need the

information that the old PATH_INFO variable provided. For this

purpose, Apache 1.2 (1.2b3 and later) sets an additional

variable, FILEPATH_INFO. This environment variable contains the

value that PATH_INFO would have had with Apache 1.1.1.</p>

<p>A script that wishes to work with both Apache 1.2 and

earlier versions can simply test for the existence of

FILEPATH_INFO, and use it if available. Otherwise, it can use

PATH_INFO. For example, in Perl, one might use:</p>

<example>

$path_info = $ENV{'FILEPATH_INFO'} || $ENV{'PATH_INFO'};

</example>

<p>By doing this, a script can work with all servers supporting

the CGI/1.1 specification, including all versions of

Apache.</p>

</section>

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