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CGI Programming Part 2. Input Tags. Many different ways of getting data from the user. The <input> tag is used most often. <input> has a type attribute Specifies the method with which to get data from the user. Other Attributes of <input>. name – name of an input field.
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Input Tags • Many different ways of getting data from the user. • The <input> tag is used most often. • <input> has a type attribute • Specifies the method with which to get data from the user.
Other Attributes of <input> • name – name of an input field. • value – value of an input field. • size – width of an input field. • maxlength – maximum number of characters that can be entered in an input field. • checked – whether a radio or checkbox is “turned on”. • src – url of an image.
Input Type: Text • Setting the type to text creates a text box. • For example, <input type=“text” name=“street” size = 30> • Note, name does not appear in the webpage. • It is seen only by the CGI program.
Input Type: Radio • Setting the type to radio creates a radio button. • For example, <input type=“radio” name=“title” value=“ms” checked> Ms. <br> <input type=“radio” name=“title” value=“mrs”> Mrs. <br> <input type=“radio” name=“title” value=“mr”> Mr. <br> <input type=“radio” name=“title” value=“dr”> Dr. <br> • All related radio buttons have the same name. • The values are all preset.
Input Type: Submit and Reset • submit creates a submit button to contact a CGI program. • For example, <input type=“submit” value=“Submit Form”> • reset creates a button to erase all values in a form. • For example, <input type=“reset” value=“Clear Form”> • The “value” appears in the button.
Input Type: Others • checkbox – creates a checkbox • password – creates a password field. A text field with characters displayed as ****. • button – creates a button the user can press. • file – creates a field to upload a file. • image – creates an image the user can click to submit a form.
Inputs Other Than <input> • <textarea> - multi-line text field. You can specify the rows and cols attributes. • <select> - creates a drop down menu.
Handling the Input • Input is sent to the CGI program specified in the <form> tag using either the get or post method. • It is best to write CGI programs that handle both. • Can be done by examining the environment variable, REQUEST_METHOD.
An Example $request_method = $ENV{‘REQUEST_METHOD’}; if ($request_method eq “GET”) { $query_string = $ENV{‘QUERY_STRING’}; } elsif ($request_method eq “POST”) { read(STDIN, $query_string, $ENV{‘CONTENT_LENGTH’}); }
CGI.pm • Many parts of CGI programs are repeated. • Makes sense to capture these parts for reuse. • CGI.pm is a module of Perl functions to do many common tasks. • Many functions provide shortcuts to create HTML. • Module can be used as a collection of functions or an object oriented class.
Object-Oriented Use • Can be used as an object-oriented class by: use CGI; … $q = new CGI; • Access subroutines as methods of $q • For example, print $q ->start_html();
Function-Oriented Use • Import a set of functions to be called directly. • non-object oriented is often faster than object-oriented. • Use a quoted list to tell Perl which functions to import. use CGI (“start_html”, “end_html”, “header”); • CGI.pm also defines sets of these functions. ‘standard’ and ‘html3’ are the most common. use CGI qw(:standard :html3);
header • The header function creates the HTTP header. • The default is “text/html”. • For example, print header(); creates print “Content-type: text/html\n\n”;
start_html • start_html create the HTML header • start_html can take one parameter, the title. • For example, print start_html(‘My Home Page’); creates <HTML> <HEAD> <TITLE> My Home Page </TITLE> </HEAD> <BODY>
start_html (cont.) • start_html can also take named parameters. • Specify attributes to give to the <body> tag. • For example, print start_html (-title => “My Title”, -bgcolor => “Red”); creates <html> <head> <title> My Title </title> </head> <body bgcolor = “Red”>
end_html • end_html creates the ending part of an HTML document. • For example, print end_html(); creates </body> </html>
param • param gets the parameter values sent to a CGI program. • Query String: name=Max%20Powers&job=ceo • Can get the query values by: $name = param(“name”); $job = param(“job”); • This is the scalar context.
Contexts of param • Can be called in list context with no arguments. Returns names of all parameters. • e.g. @params = param(); • Can be called in list context with an argument. Returns an array of all values for that argument. • e.g. @vals = param(“title”);
Locking Files • Many webpages allow multiple users to access the same information. • i.e. multiple user writing to the same file. • Need a mechanism to ensure consistency. • Do not want one user’s action to undo the actions of another. • A file must be locked when being written to.
flock • flock can be used to lock a file. • The syntax is flock (filehandle, mode); • Set mode to • 2 to lock a file. • 8 to unlock a file. • For example, flock (FILE, 2);
Debugging • Debugging a CGI script can be frustrating. • Browser will display “500 Internal Server Error” if any errors occur. • Some useful tips: • Run the program from the command line. • Use perl –c <filename> to see if file compiles.
