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Sending Data Using a Hyperlink

CGI/Perl Programming

By Diane Zak

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Objectives

• In this chapter, you will:

• Create a hyperlink to a CGI script• Append data to a URL• Use the CGI.pm module to parse data• Access data using the param function

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Introduction

• Changes to static web pages can only be made when the page is updated on the server– Requires human intervention

• Changes to dynamic web pages can be made in response to information sent through a hyperlink or form

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Creating a Link to a Script

• Most web pages contain text, images and hyperlinks– Hyperlinks or links appear as different colored text,

underlined text, or clickable images– The HTML anchor tag <A> with the HREF property is

used to create a link• HREF = Hypertext Reference• Syntax: <A HREF=URL>hyperlinktext</A>• hyperlinktext is the clickable text• <A HREF=URL><IMG SRC=imageFile></A> is the

syntax for a clickable image

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Creating a Link to a Script

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Creating a Link to a Script

• When creating a script, remember to:– Enter the shebang line (required for

UNIX)– Enter a comment that includes the

name of the script and the script’s purpose

– Enter the Content-type line:• print “Content-type: text/html\n\n”;

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print Function• Perl can generate HTML output in various

ways:– print– printf– “here” documents

• Syntax for print:– print output;

• Output can be strings, functions, variables• Output can be an expression or a list of

expressions, separated by commas

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print Function• Using the newline character (\n) can

make HTML code easier to read when viewing the HTML source in a browser– Without \n, the HTML code appears all on

one line, and is difficult to read

• It is good practice to include all of the HTML tags - HTML, HEAD, and BODY

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Completing a Script

• Remember that the following needs to be done for each Perl/CGI script that is created:1. Save the document2. cd path

If UNIX - chmod 755 filename3. perl -c filename4. perl -w filename5. Open the script in a web browser

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Sending One Item of Data Using a Link

• Append the data to the URL– Use a question mark (?) to separate the URL from

the data– Use an equal sign (=) to separate the key from

the value– Syntax:

<A HREF=URL?key=value>hyperlinkText</A>– key is the variable name

• One-word name

– value is the value that is assigned to the key

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Sending One Item of Data Using a Link

• When you have clicked on a link that is sending data, the data is viewable in the browser’s address box

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Parsing Data

• Data can be sent through a URL, but the script has to be able to separate the key from the value

• This ability is part of the CGI.pm module– module = collection of prewritten code

stored in a file– Most modules use the file extension .pm,

which stands for perl module

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Parsing Data

• Can find if you have cgi.pm by:– whereis cgi.pm (UNIX)– Start --> Search --> cgi.pm (Windows)– If not, can download from:

• http://www.genome.wi.mit.edu/ftp/pub/software/WWW/cgi_docs.html

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Parsing Data• To use CGI.pm, you need to include the

statement:– use CGI qw(:standard);

• qw = quote words• Same as the statement -

use CGI(‘:standard’);• :standard is an import tag

– Tells the Perl interpreter to allow the use of the standard features of the CGI.pm module

• Can find out more about CGI.pm, by typing:– perldoc CGI.pm

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Parsing Data

• The param function accesses the value associated with a key– param is part of the standard features

of CGI.pm– Syntax:

• param(key) where key is in single or double quotation marks

• Example:– param(‘state’);– param(“state”);

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Parsing Data• When checking for errors, using

perl -w scriptname, you can:– Type key=value after the scriptname– Example:

• perl -w jackson.cgi state=Alabama

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Parsing Data• You can also type in key=value on

a separate line– Example:

• perl -w jackson.cgi• “(offline mode: enter name=value pairs

on standard input)” message should appear

• Type in key=value pairs• Type Ctrl+d (UNIX) or Ctrl+z (Windows)

when done

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Parsing Data

• If the offline mode message does not appear, the use CGI statement needs to be changed:– use CGI qw(:standard -debug);– This is including the -debug pragma,

and tells CGI.pm to pause to let you type in the data• pragma = special type of Perl module.

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Parsing Data

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Parsing Data

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Sending Multiple Items of Data Using a Link

• When sending more than 1 item of data through a link, use the following syntax:<A HREF=URL?key1=value1&key2=value2...&keyN=valueN>hyperlinkText</A>– An ampersand (&) is used to separate each

key and value pair– Some browsers limit the amount of

information that can be attached to a URL

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Sending Multiple Items of Data Using a Link

• When sending a value that contains more than one word, substitute a plus sign (+) for a space– Example:

• <A HREF=“http://yourservername/cgi-bin/chap02/jackson.cgi?state=Arkansas&cap=Little+Rock”>Arkansas</A>

• The jackson.cgi script, when sent that data can get the values of the state and cap keys using param

– print “The capital of “, param(‘state’), “ is “, param(‘cap’), “.\n”;– The capital of Arkansas is Little Rock.

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Sending Multiple Items of Data Using a Link

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Summary• The syntax for creating a hyperlink is:

<A HREF=URL>hyperlinkText</A>– hyperlinkText is the clickable link

• The syntax for creating an image link is:<A HREF=URL><IMG SRC=imageFile></A>– imagefile contains the path and name of the image file

• print output; can be used to generate HTML instructions.– output is an expression or list of expressions separated by

commas

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Summary• To pass one item of data to a script, using a hyperlink, use the

syntax:<A HREF=URL?key=value>hyperlinkText</A>– key is the variable name associated with the value

• To pass more than one item of data to a script, using a hyperlink, separate the key and value pairs with a &, with the syntax:<A HREF=URL?key1=value1&key2=value2...&keyN=valueN>hyperlinkText</A>

• To pass a value that has a space in it, replace the space with a plus sign (+)

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Summary• The CGI.pm module can be used to parse data

– use CGI qw(:standard);

• When testing the script from the command line, with perl -w, you can either:– Enter the data on the same line as the command– Enter each item of data on a separate line– You may need to use the -debug pragma

• You can use CGI.pm’s param function to access the value of a key that was passed to the script