cgi programming part 2
DESCRIPTION
CGI Programming Part 2. Input Tags. Many different ways of getting data from the user. The tag is used most often. has a type attribute Specifies the method with which to get data from the user. Other Attributes of . name – name of an input field. - PowerPoint PPT PresentationTRANSCRIPT
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.• 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 isflock (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.