CGI Programming

Institute for Visualization and Perception ResearchI VPR 1

© Copyright 1998 Haim Levkowitz

CGI Programming• The Common Gateway Interface (CGI)• Generic script ...• Client-server interaction ...• Accessing Form Input ...• Output from the Common Gateway Interface• Forms and CGI• Server Side Includes• Hypermedia Documents• Advanced forms and gateways ...• Advanced Form Applications• Multiple Form Interaction



The Common Gateway Interface (CGI)• What Is CGI? ...

• CGI Applications ...

• Some Working CGI Applications ...

• Internal Workings of CGI ...

• Configuring the Server ...

• Programming in CGI ...

• CGI Considerations ...



What Is CGI? ...

• Communicate with other programs on server

• Pass data to program

• Process data

• Response back to browser

• Model ...



Model ...

• Browser server application

CGI

Form

CGI program's response

CGI program's response

Submit completed form

Call CGI



CGI Applications ...

• Interactive

• User ask questions, run app's

• Forms ...

• Gateways ...

• Virtual documents ...



Forms ...• Subset of HTML• User supply information• Graphical widgets for form creation

• Radio buttons, text fields, checkboxes, selection lists

• Submit button send info to server• Execute program associated with form

• Back-and-forth interaction



Gateways ...• Programs/scripts

• Access info not readable by client

• E.g., SQL queries to read database ...

• E.g., Archie, WAIS, any other Internet info service

• Use forms to query, search

• Retrieve & display dynamic, virtual documents



Virtual documents ...

• Create on the fly; response to info query

• HTML, plain, image, audio

• Simple example ...

• More sophisticated example: Art gallery ...



Simple example ...

• Welcome to IVPR's WWW Server!

• You are visiting from cs.uml.edu. The load average on this machine is 1.25.

• Happy navigating!

• Dynamic information



More sophisticated example: Art gallery ...• Form for user info• Search field for user-searches• E-mail/store form info• Response

• Image of requested painting w/info on painting• Form w/ image processing options

• Or message: doesn't exist



Some Working CGI Applications (old) ...• Lycos: www.lycos.com• Coloring book: www.ravenna.com/coloring• ArchiePlex gateway:

http://pubweb.nexor.co.uk/public/archie/archieplex/archieplex.html

• Guestbook with world map: www.cosy.sbg.ac.at/rec/guestbook

• Japanese <-> English dictionary: www.wg.omron.co.jp/cgi-bin/j-e?SASE=jfield.html• or http://enterprise/ic.gc.ca/cgi-bin/j-e



Internal Workings of CGI ...• Programs in cgi-bin, w/ certain file extensions

(usually)• User open URL ==> client sends request to server,

ask for file• Server tries to execute program in file• E.g., ...• Program gets input from STDIN ...• Program sends output on STDOUT ...• Out directly to client or via server ...



E.g., ...

• GET /cgi-bin/welcome.pl HTTP/1.0• Accept: www/source• Accept: text/html• Accept: image/gif• User-Agent: Lynx/2.4 libwww/2.14• From: [email protected]• All files in cgi-bin recognized as programs• Data formats accepted by client



Program gets input from STDIN ...

• + UNIX environment variables

• Input search string, format, length, remote host & user, other client info, server name, comm. protocol, server sw



Program sends output on STDOUT ...• Program creates output/gives URL of

existing• Send as data stream

• HTTP header (at least format - HTML, plain text, gif, )

• Blank line (= end of header)• Body (data in appropriate format - not

modified by server)



Out directly to client or via server ...

• If complete HTTP header ==> directly to client

• OW, to server• Adds complete header info• Sends to client using HTTP protocol

• E.g., with complete header ...• E.g., with partial header ...



E.g., with complete header ...HTTP/1.0 OK

Date: Tuesday, 9-April-96 11:37:00 GMT

Server: NCSA/1.4.2

MIME-Version: 1.0

Content-type: text/html

Content-length: 2000

<HTML>

<HEAD><TITLE>Welcome to IVPR's WWW Server!</TITLE></HEAD>

<BODY>

<H1>Welcome!</H!>

.

.

</BODY>

</HTML>



E.g., with partial header ...

Content-type: text/html

<HTML>

<HEAD><TITLE>Welcome to IVPR's WWW Server!</TITLE></HEAD>

<BODY>

<H1>Welcome!</H!>

.

.

</BODY>

</HTML>



Configuring the Server ...

• ServerRoot• /usr/local/etc/httpd (in httpd.conf)

• ScriptAlias• /cgi-bin/ /usr/local/etc/httpd/cgi-bin

• E.g., http://domain/cgi-bin/welcome <--> /usr/local/etc/httpd/cgi-bin/welcome

• Can have multiple CGI script directories• Can run programs anywhere (dangerous!) ...



Can run programs anywhere (dangerous!) ...

• AddType

• application/x-httpd-cgi .pl .sh .cgi

• In srm.conf ==> exec files w/ given extensions



Programming in CGI ...

• Which programming language? Features ...• AppleScript (Mac only) ...• C/C++ (UNIX, Mac, Windows) ...• C shell (UNIX only) ...• Tcl (UNIX only) ...• Visual Basic (Windows only) ...• Perl (UNIX, Mac, Windows) ...



Which programming language? Features ...

• Ease of text manipulation

• Interface w/other sw libs and utilities

• Access environment variables (in UNIX)



AppleScript (Mac only) ...• Integral part of MacOS 7.5 +• No inherent pattern matching

• Extensions• Interface w/ other Mac app's through

AppleEvents• E.g., present form to user, decode

contents, query & search Microsoft FoxPro database



C/C++ (UNIX, Mac, Windows) ...

• No database extensions

• No inherent pattern matching

• Modules/function

• +: Compiled



C shell (UNIX only) ...

• No pattern matching• ==> Must use e.g., sed or awk

• uncgi sw tool (in C)• Decode form data + store in shell envi.

vars.• No direct database access• Bugs & limitations



Tcl (UNIX only) ...

• Shell, tcsh• Simple constructs, a little more diff.

than Perl• Extensions to database and graphic

libs.• Supports regular expressions

• Insufficient handling at compile time



Visual Basic (Windows only) ...

• Communicate with other Windows programs

• No string manipulations



Perl (UNIX, Mac, Windows) ...• Most widely used• Highly portable• Powerful string manipulation op's, functions for

binary data• Simple, concise constructs• Easy calling shells, equivalents of UNIX systems

functions• Extensions (e.g., oraperl for Oracle)• Perl primer ...



CGI Considerations ...

• Data readable by client?

• Text/HTML ok

• Others: need gateway to translate

• How to present?

• E.g., Graphics, plots



Generic script ...• 1. Print header w/ Content-type declaration• 2. Print start of HTML doc.• 3. Try to get query string• 4. No string ==> user's 1st access

• Create searchable doc. w/ <ISINDEX> or <FORM>• 5. Query string: create doc w/ result of request / ack

request processed• 6. Print end of HTML doc, inc. signature• 7. Exit• skeleton.pl



Client-server interaction ...

• Input to the Common Gateway Interface



Input to the Common Gateway Interface

• Introduction ...

• Using Environment Variables ...



Introduction ...

• In CGI environment variables

• Info about client, server, user

• Form data from user

• In environment variable / body of request

• Add'l pathname info



Using Environment Variables ...• List of CGI Environment variables

• Perl: %ENV associative array• Example: About this server ...• Example: Check the client browser ...• Restricting access for specified domains ...• User authentication and identification ...• Where did you come from? ...



Example: About this server ...about_this_server.pl

Typical output

<HTML>

<HEAD><TITLE>About this Server</TITLE></HEAD>

<BODY><H1>About this Server</H1>

<HR><PRE>

Server Name: cs.uml.edu

Running on Port: 80

Server Software: NCSA/1.4.2

Server Protocol: HTTP/1.0

CGI Revision: CGI/1.1

<HR></PRE>

</BODY></HTML>



Example: Check the client browser ...

• check_browser.pl



Restricting access for specified domains ...

• Different documents for internal, external users

• restrict_domain.pl



User authentication and identification ...

• Access restricted

• Need user name & password

• Unencrypted: DON'T use real

• Server passes in REMOTE_USER env. var.

• Identify users ...



Identify users ...

• $remote_use = $ENV{'REMOTE_USER'};• if ($remote_user eq "haim") {

• print "Who are you?", "\n"• } elseif ($remote_use eq "john") {

• print "Hi John." "\n";• }



Where did you come from? ...• Last URL you were before coming here• HTTP_REFERER env. var. (from client)• referer.pl• Not all browsers set var.• Not set for first server accessed• Meaningless if accessed from bookmark /

straight typing of URL• ==> Not entirely accurate



Accessing Form Input ...• Form interaction with CGI ...

• Query strings ...

• Simple form ...

• GET and POST methods ...

• Encoded data ...

• Extra Path Information ...

• Other Languages Under UNIX

• Other Languages Under Microsoft Windows

• Other Languages on Macintosh Servers

• Examining Environment Variables



Form interaction with CGI ...• Browser Server Application

NETWORK

1. User requests a form

Retrieves form

2. Sends form to clientUser fills out form

3. User submits form

4. Forwards to CGI Application Process data

5. Output to server

T



Query strings ...• http://domain/cgi-bin/program?query-string

• Call program • Store query-string (after ?) in QUERY_STRING• E.g., name.pl

• http://domain/cgi-bin/name.pl?fortune• http://domain/cgi-bin/name.pl?finger• http://domain/cgi-bin/name.pl

• Security warning ...



Security warning ...

• Caution not to execute system commands

• NEVER: print `$query_string`;

• E.g., rm -fr /

• ==> delete everything



Simple form ...

• Form: simple_form.html• Script: unix.pl (GET version)• GET method ==>

• All form data in URL ==>• Can also access directly

• http://domain/cgi-bin/unix.pl?command=fortune

• Same result as with form



GET and POST methods ...POST: server sends data to program as input stream

<FORM ACTION="unix.pl" METHOD="POST">

==> Request

POST /cgi-bin/unix.pl HTTP/1.0

.

(header)

.

Content-length: 15

command=fortune

unix.pl (POST version, both version)

GET version only down to here



Encoded data ...

• GET ==> form info as part of URL

• ==> No spaces, special character

• ==> Encoding

• HTML form ...

• Clients issues request ...



HTML form ...• birthday.html• <HTML>• <HEAD><TITLE>When's your birthday?</TITLE></HEAD>• <BODY>• <H1>When's your birthday?</H1>• <HR>• <FORM ACTION="birthday.pl" METHOD="POST">• Birthday (in the form of mm/dd/yy): <INPUT TYPE="text" NAME="birthday"

SIZE=40>• <P>• <INPUT TYPE="submit" VALUE="Submit Form!">• <INPUT TYPE="reset" VALUE="Clear Form">• </FORM>• <HR>• </BODY>• </HTML>



Clients issues request ...Enter: 08/30/53

POST /cgi-bin/birthday.pl HTTP/1.0

.

. (information)

.

Content-length: 21

birthday=08%2F30%2F53

Decode "%2F" to "/”

Program: birthday.pl ...



Program: birthday.pl ...#!/usr/local/bin/perl

$size_of_form_information = $ENV{'CONTENT_LENGTH'};

read (STDIN, $form_info, $size_of_form_information);

$form_info =~ s/%([\dA-Fa-f][\dA-Fa-f])/pack ("C", hex ($1))/eg; ...

($field_name, $birthday) = split (/=/, $form_info);

print "Content-type: text/plain", "\n\n";

print "Hey, your birthday is on: $birthday. That's what you told me, right?", "\n";

exit (0);



$form_info =~ s/%([\dA-Fa-f][\dA-Fa-f])/pack ("C", hex ($1))/eg; ...• s: substitute; starts with %• ( ): store in var. ($1)• 2 chars., [\dA-Fa-f]: digit or letter A-F (or a-f)• /pack ("C", hex ($1)): convert val. in $1 to

ASCII equiv.• e: eval replacement string as expression• g: replace all occurrences of hexa. string



Extra Path Information ...• Can pass as part of URL• Server needs to know where name of prog. ends

• Understand that what's following is extra• http://domain/cgi-bin/display.pl/cgi/cgi_doc.txt

• /cgi/cgi_doc.txt --> PATH_INFO• Set PATH_TRANSLATED, map info in PATH_INFO to doc.

root dir.• Can use PATH_INFO + DOCUMENT_ROOT (not set by all

servers• $path_translated = join ("/",

$ENV{'DOCUMENT_ROOT'}, $ENV{'PATH_INFO'};



Output from the Common Gateway Interface• Overview ...• CGI and Response Headers ...• Accept Types and Content Types ...• The Content-length Header ...• Server Redirection ...• The “Expires” and “Pragma” Headers ...• Status Codes ...• Complete (Non-Parsed) Headers ...



Overview ...

• Execute program• Return output in a way browser can handle• Output to browser

• Plain text / HTML• Graphics / binary• HTTP status codes• Tell server to send a document



CGI and Response Headers ...• Valid HTTP headers ...• Netscape-compatible headers ...• Complete list:

http://www.w3.org/hypertext/WWW/Protocols/HTTP/Object_Headers.html

• Header lines don't have to be in any special order

• Header block must end with blank line



Valid HTTP headers ...

• Content-length: in bytes• Content-type: MIME type• Expires: expiration date & time of doc.

==> reload• Location: server redirection• Pragma: Turn doc. caching on/off• Status: of request



Netscape-compatible headers ...

• Refresh: client reloads specified doc.

• Set-cookie: client stores specified data

• Keep track of data between requests



Accept Types and Content Types ...

• CGI can handle any type that client can

• E.g., plain, HTML, PS, PDF, SGML, ...

• Client sends list of "accept types"

• Supports directly / via helper app's

• Server stores in HTTP_ACCEPT

• Code to check, accept JPEG or GIF? ...



Code to check, accept JPEG or GIF? ...

#/usr/local/bin/perl

$gif_image = "logo.gif";

$jpeg_image = "logo.jpg";

$plain_text = "logo.txt";

$accept_types = $ENV{'HTTP_ACCEPT'};

if ($accept_types =~ m|image/gif|) {

$html_document = $gif_image;

} elseif ($accept_types =~ m|image/jpeg|) {

$html_document = $jpeg_image;

} else {

$html_document = $plain_text;

}



The Content-length Header ...

• Entire file: contents_length.pl• stat command to get contents length• 13 element array; [7] is file size in

bytes• Good for small graphics, not for large

• In pieces: gif_pieces.pl



Server Redirection ...

• Retrieve existing doc from somewhere• Send location header: tell server which doc.• Result appears as if client requested doc. not

prog.• "Canned" response• E.g., thanks.html ...• Simple redirection code ...• Decide what gets returned based on ...



E.g., thanks.html ...<HTML>

<HEAD><TITLE>Thank You!</TITLE></HEAD>

<BODY>

<H1>Thank You!</H1>

<HR>

Thank You for filling out this form. We will be using your input to improve our products.

Thanks again,

WWW Software, Inc.

</BODY>

</HTML>



Simple redirection code ...#!/usr/local/bin/perl

print "Location: /thanks.html", "\n\n";

exit (0);

Can't return content type headers

Can return any location on web



Decide what gets returned based on ...

E.g., load

#!/usr/local/bin/perl

$uptime = `/usr/ucb/uptime`;

($load_average) = ($uptime =~ /average: ([^,]*)/);

$load_limit = 10.0;

$simple_document = "/simple.html";

$complex_document = "/complex.html";

if ($load_average >= $load_limit) {

print "Location: $simple_document", "\n\n";

} else {

print "Location: $complex_document", "\n\n";

}

exit (0);



The "Expires" and "Pragma" Headers ...

• Caching stores virtual doc.

• ==> CGI prog. not run again ==> out-of-date

• E.g., click for date and time ...

• Click again, date/time same, should be diff. ...



E.g., click for date and time ...#!/usr/local/bin/perl

chop ($current_date = `/bin/date`);

$script_name = $ENV{'SCRIPT_NAME'};

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

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

print "<HEAD><TITLE>Effects of Browser Caching</TITLE></HEAD>", "\n";

print "<BODY><H1>", $current_date, "</H1>", "\n";

print "<P>", qq|<A HREF="$script_name">Click here to run again!</A>|, "\n";

print "</BODY></HTML>", "\n";

exit (0);



Click again, date/time same, should be diff. ...

• Contents from cached doc. rather than prog.

• To fix, tell browser not to cache ...

• Or cause to expire ...

• But some browsers don’t handle correctly



To fix, tell browser not to cache ...



print "Pragma: no-cache", "\n\n";



Or cause to expire ...



print “Expires: Tuesday, 16-April-96 17:30:00 GMT", "\n\n";



Status Codes ...

• Codes ...

• Example ...



Codes ...• 200: Success• 204: No response ...• 301: Document moved• 401: Unauthorized • 403: Forbidden• 404: Not found• 500: Internal server error• 501: Not implemented



204: No response ...

• Don’t load new page

• Good for invalid values in forms, or clicks on unassigned sections in imagemaps

• E.g., ...



E.g., ...#!/usr/local/bin/perl

print "Content-type: text/plain", "\n";

print "Status: 204 No Response", "\n\n";

print "You should not see this message. If you do, your browser does", "\n";

print "not implement status codes correctly.", "\n";

exit (0);



Example ...#!/usr/local/bin/perl

$remote_host = $ENV{'REMOTE_HOST'};

print "Content-type: text/plain", "\n";

if ($remote_host eq "uml.edu") {

print "Status: 200 OK", "\n\n";

print "Great! You are from UMass Lowell!", "\n";

} else {

print "Status: 400 Bad Request", "\n\n";

print "Sorry! You need to access this from UMass Lowell!", "\n";

}

exit (0);



Complete (Non-Parsed) Headers ...• So far, partial HTTP headers (Content-type)• Can generate complete header• ==> No overhead on server

• Output goes directly CGI prog. --> client ...• ==> + Faster response• ==> – Careful! Server can’t avoid errors• Programs start with “nph-” (non-parsed header)• E.g., this will count in real time ...• But, with partial header, not! ...



Output goes directly CGI prog. --> client ...

• .

BrowserServer

CGI Application

Partial header

Complete header

Server response with Complete header



E.g., this will count in real time ... #!/usr/local/bin/perl

$server_protocol = $ENV{'SERVER_PROTOCOL'};$server_software = $ENV{'SERVER_SOFTWARE'};

print "$server_protocol 200 OK", "\n";print "Server: $server_software", "\n";print "Content-type: text/plain", "\n\n";

print "OK, Here I go. I am going to count from 1 to 50!", "\n";

for ($loop=1; $loop <= 50; $loop++) { print $loop, "\n"; sleep (2);}

print "All Done!", "\n";

exit (0);



But, with partial header, not! ...

• Leave only Content-type

• Remove nph- from name

• Result is entire document at once



Forms and CGI

• HTML Form Tags ...

• Sending Data to the Server ...

• Designing Applications Using Forms in Perl ...

• Decoding Forms in Other Languages



HTML Form Tags ...• <FORM ACTION="/cgi-bin/prog.pl" METHOD="POST">• <INPUT TYPE="text" NAME="name" VALUE="value" SIZE="size">• <INPUT TYPE="password" NAME="name" VALUE="value"

SIZE="size">• <INPUT TYPE="checkbox" NAME="name" VALUE="value">• <INPUT TYPE="radio" NAME="name" VALUE="value">• <SELECT NAME="NAME" SIZE=1>• <OPTION SELECT>ONE• <OPTION>Two• </SELECT>• More form Tags ...



More form Tags ...

• <SELECT NAME="NAME" SIZE=n MULTIPLE>• <TEXTAREA ROWS=yy COLS=xx NAME="name">• </TEXTAREA>• <INPUT TYPE="submit" VALUE="Message">• <INPUT TYPE="submit" NAME="name"

VALUE="value">• <INPUT TYPE="image" SRC="/image"

NAME="name" VALUE="value">• <INPUT TYPE="reset" VALUE="Message">



Sending Data to the Server ...

• MIME type to encode form data: application/x-www-form-urlencoded

• Equate each NAME with entered value• key-value_pair&key-value_pair&key-value_pair• text, password: value = user input [blank]• radio: value = [on]; unchecked ==> ignored• GET vs. POST ...• Decoding form data ...



GET vs. POST ...• GET

• + Access CGI prog. w/ query without a form• Pass parameters to program ...• Can send extra path info ...

• – Query might get truncated• Post

• + Unlimited query length• – No “canned” queries



Pass parameters to program ...

• <A HREF="cgi-bin/prog.pl?user=Haim%20Levkowitz&Occupation=Professor">CGI Program</A>

• Need to encode spaces, special char's

• encode.pl (not a CGI prog!)



Can send extra path info ...

• <A HREF="cgi-bin/prog.pl/user=Haim%20Levkowitz/Occupation=Professor">CGI Program</A>



Decoding form data ...

• REQUEST_METHOD: how data passed by client• GET: get QUERY_STRING / PATH_INFO from

env. var.• POST: read CONTENT_LENGTH bytes from

STDIN• Split query string on “&” (key=value&key=value ...)• Decode hexadec. and “+” in key-value pairs• Create key-value table, key as index



Designing Applications Using Forms in Perl ...

• Simple form: Testing A Form

• Form: name.html

• Program: greeting.pl

• Combining graphics and queries

• Form: color_text.html

• Program: gd_text.pl



Server Side Includes• Introduction ...

• How SSI work? ...

• Configuration ...

• Environment Variables ...

• Including Boilerplates ...

• File Statistics ...

• Executing External Programs ...

• Executing CGI Programs ...

• Tailoring SSI Output ...

• Common Errors ...



Introduction ...

• Directives in HTML doc ...

• Execute progs, output data, e.g., envi. vars.

• Not all servers support

• CERN: no; NCSA, Netscape: yes

• fakessi.pl simulates



Directives in HTML doc ...

Command Parameter Description echo var Insert value of SSI/envi. vars. include Insert text of doc. into curr. file file Pathname relative to curr. dir. virtual Virtual path to doc. on server fsize file Insert size of spec'd file flastmod file Insert last mod data/time exec Exec. ext.prog; output -> cur. doc cmd Any application on host cgi CGI program config Modify aspect of SSI errmsg Default error message sizefmt Format for size of file timefmt Format for dates



How SSI work? ...

• Client request doc. from SSI-enabled server• Server parsed doc., returns evaluated doc. ...• No auto parsing of all files, only those configured• Powerful, but

• Expensive: computational load parsing• Security risk: directives to exec risky sys

commands



Server parsed doc., returns evaluated doc. ...

Server

Process SSI Statements

Browser

Visitor HTML

HTMLw/SSI

Request document

Retrieve document from file system

1234



Configuration ...

• Extensions of files server should parse (srm.conf) ...

• Access configuration (access.conf) ...



Extensions of files server should parse (srm.conf) ...

• .shtml: • AddType text/x-server-parsed-html

.shtml• All HTML:

• AddType text/x-server-parsed-html.html• ==> Performance degradation



Access configuration (access.conf) ...

• Includes: embed SSI directives to display env. vars. & file stats. in HTML docs.

• Exec: execute external programs from HTML docs.

• Options Includes ExecCGI

• Options IncludesNoExec



Environment Variables ...

• • DOCUMENT_NAME current file• DOCUMENT_URI virtual path to file• QUERY_STRING_UNESCAPED undecoded query string,

shell metachars escaped w “\”• DATE_LOCAL current date & time (local)• DATE_GMT current date & time (GMT)• LAST_MODIFIED last mod’n date & time



Including Boilerplates ...

• Include file in HTML doc

• 



File Statistics ...

• The size of the file is  bytes

• It was last modified on  .



Executing External Programs ...• Execute CGI / sys program• Output in HTML doc• Welcome . Here is

some info about you:• <PRE></PRE> • ==> Finger user in var.• WARNING: strip SSI commands from input

• E.g., 



Executing CGI Programs ...

• E.g., access counter

• This page has been accessed  times



Tailoring SSI Output ...• • • 

• %D: Date as “%m/%d/%y” (04/16/96)• %r: Time as “%I:%M:%S AM | PM” (05:00:00

PM)• 21 SSI Time formats

• Table omitted



Common Errors ...

• • No “#”

• • Space between “-” and “#”

• ==> Whole expression treated as HTML comment • No error message!



Hypermedia Documents

• Graphics creation and manipulation w/ CGI• Creating Dynamic Home Pages ...• CGI Examples with PostScript ...• The gd Graphics Library• CGI Examples with gnuplot• CGI Examples with pgperl• Animation ...



Creating Dynamic Home Pages ...

• Creating Dynamic Home Pages ...Tell server to exec CGI prog ...

• E.g., greeting with time of access

• homepage_welcome.pl



Creating Dynamic Home Pages ...• Tell server to exec CGI prog• Instead of displaying HTML file• In srm.conf:

• AddType application/x-httpd-cgi index.html

• CERN server (httpd.conf): • Exec /index.html /usr/local/etc/httpd/cgi-

bin/index.pl



CGI Examples with PostScript ...• Dynamic graphics• PostScript on screen same as on page• Run through interpreter (browsers don't handle PS)

• E.g., GNU GhostScript (http://www.phys.ufl.edu/docs/goodies/unix/previewers/ghostscript.html)

• ==> GIF image to browser• E.g., http://domain/cgi-bin/ps_time.pl• Or <IMG SRC="/cgi-bin/ps_time.pl">



Animation ...

• Client pull ...

• Server push ...



Client pull ...

• New HTTP connection for ea. requested doc

• E.g. display time continuously w/ HTML ...

• And with Perl ...

• E.g., random fortune message every 10 secs. ...



E.g., display time continuously w/ HTML ...

<META HTTP-EQUIV="Refresh" CONTENT=5>





And with Perl ...

• #!/usr/local/bin/perl

• $delay = 5;• $date = "/bin/date";

• print "Refresh: ", $delay, "\n";• print "Content-type: text/plain", "\n\n";• print `$date`;

• exit(0);



E.g., random fortune message every 10 secs. ...#!/usr/local/bin/perl

$fortune = "/usr/local/bin/fortune";$refresh_time = 10;

print "Refresh: ", $refresh_time, "\n";print "Content-type: text/plain", "\n\n";

print "Here is another fortune...", "\n";print `$fortune`;

exit(0);



Server push ...

• Connection open till all data received

• multipart/x-mixed-replace MIME type

• E.g., server_push.pl