Changing your htbin scripts to CGI scripts

If you have upgraded your server from NCSA httpd 1.0a5 to NCSA httpd 1.0, you have probably discovered that your old scripts don't work in their ScriptAlias locations. This is because NCSA httpd 1.0 implements the CGI specification.

CGI stands for the Common Gateway Interface. It is the next generation of the script interface, called Common because many of the major HTTP servers will be implementing it.

To use your scripts with CGI, you will have to change a few minor semantic things to reflect the fact that CGI passes information in different locations than htbin did.

Method

Whether your script is a GET script or a POST script, you should check that your script is being accessed with the proper method. This can be done with the environment variable REQUEST_METHOD. This variable will be either GET, HEAD, or POST depending on which method was used to access your script.

The command line

For GET scripts, argv[1] used to be path information, and argv[2] used to be the query string. This information can now be found in the environment variables PATH_INFO and QUERY_STRING respectively.

In addition, for non-form GET requests, the query string will be decoded and placed on the command line. If you are writing a script to handle forms, you will not get this information on the command line.

For POST scripts, argv[1] used to contain the content length. This has been moved into the environment variable CONTENT_LENGTH.

DocumentRoot and ServerRoot

Because the environment variables DOCUMENT_ROOT and SERVER_ROOT may have no equivalent in server packages besides NCSA httpd, these have been removed from the CGI specification. You should not have need of this data unless you are looking for the unescape support program.

The Location: output header

If you used the Location: output header for scripts, you'll note that URL specifications still work, but file paths are no longer absolute filesystem paths. They are now virtual paths. This means the server will perform Alias and DocumentRoot translation on this path before retrieving the document.

There are many more features in the specification which you will want to take advantage of. The amount of information now given to the script is much greater than it was.

Rob McCool, robm@ncsa.uiuc.edu