CGI Environment Variables

 

 

Environment Variables

 

CGI protocol is defined with a collection of environment variables that hold data set up by a browser. It defines methods such as GET and POST for sending data, and how much data will be sent to server. Other environment variables contain such information as visitor's IP address, visitor's browser type, etc. All the environment variables are stored in the special hash array or associate array called %ENV which is set each time when a script is called.

 

 

A list of environment variable defined by CGI standard is as shown below:

 

AUTH_TYPE

If the server supports user authentication, and the script is protects, this is the protocol-specific authentication method used to validate the user.

 

CONTENT_TYPE

It specifies the media type of the data for queries, which have attached information, such as HTTP POST and PUT, this is the content type of the data.

 

CONTENT_LENGTH

The length (number of bytes) of information passed to the script.

 

GATEWAY_INTERFACE

The name and version of the protocol being used by the server to communicate with the script. Format: CGI/revision

 

PATH_INFO

It provides any extra path information, as given in the URL, for accessing this script. The extra information is sent as PATH_INFO to be decoded by the server before it is passed to the CGI script.

 

PATH_TRANSLATED

It gives the absolute file system path for access the script. The server provides a translated version of PATH_INFO, which takes the path and does any virtual-to-physical mapping to it.

 

QUERY_STRING

Any additional information passed to the script after the ? mark in the URL which referenced this script is called the query information. It should not be decoded in any fashion.

 

 

 

REMOTE_HOST

It contains a fully qualified domain name of the client computer. If the host name cannot be determined, it should set REMOTE_ADDR to hold the IP address of the host and leave this variable unset.

 

REMOTE_ADDR

The IP address of the remote client computer making the request.

 

REMOTE_IDENT

The client machine's username. Usage of this variable should be limited to logging only.

 

SCRIPT_NAME

A virtual path to the script being executed, used for self-referencing URLs.

 

REMOTE_USER

The name used to authenticate the user for accessing the script.

 

SERVER_SOFTWARE

The name and version of the information server software answering the request (and running the gateway).

# Format:

     name/version

 

SERVER_NAME

The server's hostname, DNS alias, or IP address as it would appear in self-referencing URLs.

 

SERVER_PROTOCOL

The name and revision of the information protocol this request came in with. Format: protocol/revision

 

SERVER_PORT

The port number to which the request was sent.

 

REQUEST_METHOD

The method with which the request was made. For HTTP, this is "GET", "HEAD", "POST", etc.

 

HTTP_ACCEPT

Gives a comma-separated list of MIME types that the client can accept.

 

HTTP_REFERER

Provides the address of the page where the request originated.

 

 

HTTP_USER_AGENT

Specifies the name of the client program used to make the request.

 

 

Errors Codes for Client and Server

 

When there is an error the corresponding error code will be sent to client and the message will then displayed for the client. The error codes are as shown below.

 

Client Errors Code

400                 Bad Request

401                 Unauthorized

402                 Payment Required

403                 Forbidden

404                 Not Found

405                 Method Not Allowed

406                 Not Acceptable

407                 Proxy Authentication Required

408                 Request Timeout

409                 Conflict

410                 Gone

411                 Length Required

412                 Precondition Failed

413                 Request Entity Too Large

414                 Request-URI Too Long

415                 Unsupported Media Type

416                 Requested range not valid

417                 Failed

418                 Failed

 

Server Error

500                 Internal Server Error

501                 Not Implemented

502                 Bad Gateway

503                 Service Unavailable

504                 Gateway Timeout

505                 HTTP Version Not Supported

506                 Redirection failed

 


 

HTTP Status Codes

 

HTTP Working Group: http://www.w3.org/Protocols/HTTP

RFC 2616(HTTP 1.1):http://www.cis.ohio-state.edu/htbin/rfc/rfc2616.html

 

 

100                   Continue

101                   Switching Protocols

199                   Misc.                 

 

Successful Codes

 

200                   OK, the request was fulfilled

201                   Created, following a POST command, indicates the URI by which the newly created document should be known

202                   Accepted, the request has been accepted for processing, but the processing has not been completed

203                   Non-Authoritative Information

204                   No Content

205                   Reset Content

206                   Partial Content

299                   Miscellaneous information

 

Redirection Codes

300                   Multiple Choices, multiple documents available

301                   Moved Permanently

302                   Moved temporarily

303                   See other document

304                   Not modified since last retrieval

305                   Use Proxy

306                   Switch proxy

307                   Document moved temporarily

399                   Misc.



 

Perl CGI Programs for viewing $ENV variables

 

The first line of most CGI programs must be an HTTP header, as listed below, to inform the Web browser what type of output is expected. When the Perl print statement is used to send the script file to the browser, typical web HTML tags and display are then followed.

 

Text                             Content Type: text/plain

HTML page                Content Type: text/html

Gif graphics               Content Type: image/gif

Redirection                Location:http://www.newloca.com

Cookie                       Set-cookie:

Error Message          Status: 402

 

 

 

Example 1: You will prepare a Perl CGI script and place it in the cgi-bin directory of a desired server. In addition, you will need to prepare a simple HTML web page for linking to the Perl script for viewing portion information of your browser.

 

The Perl CGI script:

#!/usr/bin/perl

# browserinfo.pl

#

#

print "Content-type: text/html\n\n";

 

print "<HTML>\n<HEAD>\n";

print "<TITLE> Display Brwoser and some Server Info </TITLE>\n";

print "</HEAD>\n";

print "<BODY>\n";

print "<BR><BR>\n";

print "<H2>Your browser information: </H2>\n";

print "<H3>\n";

print "HTTP_USER_AGENT = $ENV{'HTTP_USER_AGENT'}<BR>\n";

print "WINDIR          = $ENV{'WINDIR'}<BR>\n";

print "REMOTE_ADDR     = $ENV{'REMOTE_ADDR'}<BR>\n";

print "SCRIPT_NAME     = $ENV{'SCRIPT_NAME'}<BR>\n";

print "</H3>\n";

print "</BODY>\n";

print "</HTML>\n";

 

The HTML Web page for calling the Perl CGI script:

 

<!-- browserinfo.html -->

 

<HTML>

<HEAD>

<TITLE> Display Browser and some Server Info </TITLE>

</HEAD>

<BODY>

<A HREF="http://149.164.36.204/cgi-bin/browserinfo.pl">

<H2>Click to view browser and server information: </H2> </A>

 

</BODY>

</HTML>

 

 

 

 

 




The Web page for client side user:

 

 

 

The output from running Perl CGI located on the server:

 

 


Example 2: This Perl CGI program, readend.pl, is placed in the cgi-bin directory. Another HTML page called readenv.html is also placed on the server.

 

The Perl CGI program:

#!/usr/local/bin/perl

# readenv.pl

#

# Execute this program to view all the environment variables.

#

print "Content-type: text/html\n\n";

 

print "<HTML><HEAD><TITLE>Environment Variables</TITLE></HEAD><BODY>";

foreach $env_var (keys %ENV)

 {

    print "<BR>";

      # Read the first field of %ENV variable

    print "<FONT COLOR=red>$env_var</FONT>";

    print " == ";

      # Hash the second field of %ENV variable

    print "<FONT COLOR=red>$ENV{$env_var}</FONT>";

}

print "</BODY></HTML>";

 

 

 

The HTML page can be either placed in the client machine or at server:

 


 

The readenv.pl is executed by the server and the send the result back to the client:

 

 

The compete list of environment variables are listed below:

 

PROMPT == $p$g
QUERY_STRING ==
CONTENT_TYPE ==
SERVER_PROTOCOL == HTTP/1.1
HTTP_REFERER ==
COMSPEC == C:\COMMAND.COM
NWLOGIN == G
PATH_TRANSLATED == C:\HTTPD\HTDOCS
HTTP_USER_AGENT == Mozilla/4.0 (compatible; MSIE 5.0; Windows 98; DigExt)
HTTP_ACCEPT == image/gif, image/x-xbitmap, image/jpeg, image/pjpeg, application/vnd.ms-excel, application/msword, application/vnd.ms-powerpoint, */*
REMOTE_HOST ==
GATEWAY_INTERFACE == CGI/1.1
REMOTE_IDENT ==
PATH_INFO ==
SERVER_SOFTWARE == OmniHTTPd/2.07
TMP == C:\WINDOWS\TEMP
WINDIR == C:\WINDOWS
REMOTE_USER ==
REMOTE_ADDR == 149.164.36.104
BLASTER == A220 I7 D1 T2
SCRIPT_NAME == /cgi-bin/readenv.pl
TEMP == C:\WINDOWS\TEMP
WINBOOTDIR == C:\WINDOWS
CMDLINE == WIN
SERVER_NAME == eet499
SNDSCAPE == C:\WINDOWS
HTTP_COOKIE ==
CONTENT_LENGTH == 0
REQUEST_METHOD == GET
VXIPNPPATH == C:\VXIPNP
PATH == C:\httpd;C:\WINDOWS;C:\WINDOWS\COMMAND;C:\PERL\BIN\;C:\WINDOWS;C:\WINDOWS\COMMAND;C:\PROGRA~1\NETWOR~1\MCAFEE~1;S:\WIN32\LOTUS\CCMAIL\;C:\PROGRAM;FILES\MTS;C:\VXIPNP\WIN95\BIN;C:\PROGRAM;FILES\MTS;C:\VXIPNP\WIN95\BIN;C:\HTTPD\PHP
AUTH_TYPE ==
SERVER_PORT == 80