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Sending Data Using a Hyperlink

Sending Data Using a Hyperlink. CGI/Perl Programming By Diane Zak. 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. Introduction.

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Sending Data Using a Hyperlink

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  1. Sending Data Using a Hyperlink CGI/Perl Programming By Diane Zak

  2. 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

  3. 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

  4. 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

  5. Creating a Link to a Script

  6. 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”;

  7. 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

  8. 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

  9. Completing a Script • Remember that the following needs to be done for each Perl/CGI script that is created: 1. Save the document 2. cd path If UNIX - chmod 755 filename 3. perl -c filename 4. perl -w filename 5. Open the script in a web browser

  10. 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

  11. 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

  12. 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

  13. 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

  14. 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

  15. 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”);

  16. 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

  17. 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

  18. 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.

  19. Parsing Data

  20. Parsing Data

  21. 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

  22. 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.

  23. Sending Multiple Items of Data Using a Link

  24. 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

  25. 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 (+)

  26. 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

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