An Introduction to Active Server Pages

An Introduction To ASP
K. Yue, copyright 2000
Created October 23, 2000

Introduction

Active Server Pages (ASP) is Mircrosoft's Web server side technology.
ASP is presentation-oriented.
ASP script code is embedded inside HTML elements.
ASP allows script to be executed by the Web server through an ASP interpreter.
Unlike CGI, ASP script is executed by Microsoft's Web server (IIS).
ASP files usually have the extension .asp. An .asp file is a text file.
The primary scripting language of ASP is VBScript.

Embedded Scripting

Server-side script commands may be enclosed by the delimiters <% and %>.
Any valid primary scripting language commands can be enclosed by the ASP delimiters.
An equal sign can be used to place values into the HTML file.

Example:

helloworld.asp

<html>
<body bgcolor="#ccffff">
<% ="Hello, world from ASP! <hr>" %>
Bye from regular HTML code.
</body>
</html>

The <% ... %> is executed by the Web server and the following HTML contents are sent to the browser.

<html>
<body bgcolor="#ccffff">
Hello, world from ASP! <hr>
Bye from regular HTML code.
</body>
</html>

Example

date.asp

Example

loop.asp

<body bgcolor="#ccffff">
<% for i = 6 to 12 %>
<div style="font-size:<% = i %>px">Hello World</div>
<% next %>
</body>

Example

Time.asp (adapted from Microsoft)

<div style="color:green">
<% If Time >= #12:00:00 AM# And Time < #12:00:00 PM# Then %>
Good Morning!
<% Else %>
Good afternoon!
<% End If %>
</div>

TimeAlt.asp: using the Response.write method to write to the server.

ASP supports other scripting languages. Example:
- JavaScript
- JScript
- PerlScript
The directive @LANGUAGE can be used to specify the scripting language.

Example:

<html>
<% @LANGUAGE="PerlScript" %>
<body bgcolor="#ccffff">
<%
$Response->Write("Hello, world! <br>");
$Response->Write("The server time is : " . (localtime));
%>
</body>
</html>

The HTML <script> element can be uesd to specify script command.
The LANGUAGE and RUNAT attributes are used to specify the script language and the location of execution (client or server).

Example

ScriptTag.asp

<html>
<head>
<script runat="SERVER" language="JSCRIPT">
function Dummy () {
Response.Write("This is a dumb way to write something.")
}
</script>
</head>
<body bgcolor="#ccffff">
<% Dummy() %>
</body>
</html>

Note that JScript is used.

Comment formats:
- <!-- HTML –>
- // JScript
- REM VBScript
- ‘ VBScript
- # Perlscript
ASP scripts can be used to generate client-side script such as:

Server-side includes (SSI) can be used to include a file into a .asp file. The syntax:

Either one of the keyword VIRTUAL or FILE should be included.
- VIRTUAL: use virtual directory of the web server.
- FILE: use relative directory of the file system.
Note that SSI may be more than one level.
It is recommended that included files use the extension .inc.
SSI is executed before other scripting commands.

Example:

(SSI.asp)

<html>
<head>
<title>An example of SSI</title>
</head>
Here is a message from script:
<p>

<% Dummy() %>
<hr>

</body>
</html>

(Dummy.inc):

(ExampleFooter.inc):

<div style="font-size=8px;color:blue">
<script language="JavaScript">

</script>
</div>
<div style="font-size=8px">
Dr. Kwok-Bun Yue <br>
Associate Professor, Computer Science <br>
Chair, Computer Information Systems Program <br>
University of Houston - Clear Lake <br>
2700 Bay Area Boulevard <br>
Houston, TX 77058
</div>

A Brief Introduction to VBScript

VBScript stands for Visual Basic Scripting Edition, a Microsoft's technology.
The following example illustrates some of the basic VBScript syntax on data types.

Example:

<%
' Option Explicit
' If used, all variables must be declared.
'
Dim A ' Declare the variable A.
A = 10
Response.Write("A: " & A & "<br>")

' Convert to Date data type.
strToday = "October 25, 2000"
MyDate = CDate(strToday)
Response.Write("strToday: " & strToday & "<br>")
Response.Write("MyDate month: ")
Response.Write(Month(MyDate) & "<br>")

' String concatenation and line continuation.
longString = "This is a long" & _
"string defined in two lines."
Response.Write("longString: " & longstring & "<br>")

Const PI = 3.141592654
Response.Write("PI: " & PI & "<br>")
' Illegal assignment: PI = 2.0
%>

The following examples illustrative simple functions and procedures.

Example:

<%
Function Celsius(fDegrees)
Celsius = (fDegrees - 32) * 5 / 9
End Function

f = 100
Response.write(f & "F is " & Celsius(f) & " Celsius.<br>")

Sub Dummy()
Response.write ("Hello from Dummy.<br>")
End Sub

Dummy()
%>

The following example illustrates object creation and the dictionary (hash) class.

Example:

<%
' Dictionary object
Dim courses ' Create a variable.
' Creating object using Server.CreateObject.
Set courses = Server.CreateObject("Scripting.Dictionary")
courses.Add "CSCI4230", "Internet Application Development"
courses.Add "CSCI4333", "Design of Database"
courses.Add "CSCI5333", "DBMS"

classnames = courses.Keys ' Get the keys.
For i = 0 To courses.Count - 1 ' Iterate the array.
   Response.Write(classnames(i) & ": " & _
                  courses.Item(classnames(i)) & _
                  "<br>") ' Return results. & ": "
Next ' i
%>

The following example illustrates object assignments and equivalence testing.

Example:

' Using set for object reference assignment
' Using 'is' for object reference test.
Set a = courses
if (a is courses) Then
   Response.Write ("a and courses refer to the same object<br>")
else
   Response.Write ("a and courses do not refer to the same object<br>")
end if

Dim b
' Invalid assignment: b = courses
' Invalid test: If (b is course)
' Both b and courses must be object
' reference for the 'is' test.
Set b = Server.CreateObject("Scripting.Dictionary")
if (courses is b) Then
   Response.Write ("b and courses refer to the same object<br>")
else
   Response.Write ("b and courses do not refer to the same object<br>")
end if

Some useful VBScript tips:
- &: String concatenation
- _: statement continues to next line.
- vbCRLF: constant for the line feed-carriage return.
- No ; at the end.
- " for string literal.
- ' for comments.
- Use "Option Explicit" as the first statement.
- Empty: uninitialized; Null: intentionally contain no data.