Windows Script Host (WSH) is a powerful, useful, and flexible facility for executing scripts in the Windows environment, but with its power comes a degree of complexity. This month, to begin an examination of WSH, I'll describe what WSH is and how it provides a way to run scripts in Windows. Then I'll look at the various types of script files and means of running them. In future articles, I'll cover the specifics of the .wsf script file format and Windows Script Components (WSC).
What Is WSH?
WSH is a Windows component that provides an environment for executing scripts at the OS level rather than in some other context (such as in a Web browser). WSH isn't a language like Perl or a script interpreter like perl.exe; it's a COM-based script host that executes scripts in Windows. WSH is a native OS component in Windows 2000 and later. You can install it on earlier platforms such as Windows NT 4.0 and Windows 98 after downloading it from Microsoft's Web site.
WSH comes with two standard scripting engines: VBScript and JScript. VBScript is commonly used in systems administration scripting, and JScript (Microsoft's implementation of JavaScript) is more widely used in Web browsers due to JavaScript's broad platform support. Depending on the task, both languages are suitable for WSH-based scripting. WSH can also execute scripts in other languages if you install the appropriate language engines.
WSH comes standard with a set of useful objects. Some of these objects, such as the WScript object and its related objects and collections, exist only in scripts executed by WSH (e.g., you can't use the WScript.Echo method in the script section of a Web page). Some of the objects, however, are general-purpose objects that you can use in any COM-compatible programming language.
There are two basic types of WSH scripts: standalone (i.e., language-specific) scripts and .wsf (Windows script file) scripts. Standalone scripts have a language-specific file extension—for example, .vbs ( VBScript) or .js (JScript). In contrast, .wsf scripts are language-neutral XML text files, and they provide some features beyond what standalone scripts provide. WSH also has two script hosts: WScript and CScript, which I'll describe shortly. The associated WSC technology, formerly known as server scriptlets, allows you to create your own COM components in a script.
Understanding the Script Hosts
You can execute WSH scripts by using the GUI-based host WScript or the console-based host CScript. These two hosts are provided by the wscript.exe and cscript.exe programs, respectively. Windows defaults to using the WScript host, but you can change this default, as I'll show you in a moment.
When you run a script with CScript, the script writes WScript .Echo output and runtime error messages to a console window (i.e., a command-prompt window). When you use Cscript at the command prompt to run a script, the script's output and errors appear in the current command window. When you use Cscript to run a script in the GUI (e.g., in Windows Explorer or in the Run dialog box), Windows creates a temporary console window for the script and executes it inside that window. The script's output and errors appear in the temporary console window, which disappears when the script is completed.
The WScript host, by contrast, executes scripts without a console window. When you use the WScript host, WScript.Echo output and runtime errors are displayed in Windows message boxes.
Both script hosts support a set of command-line options that control script execution and define the default host. The default host is the host used when you execute a script from the GUI or type only its filename at a command prompt. To see the command-line options, type one of the following commands at a command prompt:
cscript /?
or
wscript /?
(If you use the Wscript command, the usage message will appear in a Windows message box instead of in the command window.)
Table 1 shows the command-line options. Note that the script host's command-line options are prefixed with two forward slashes (//) to prevent confusion with the commandline options for user-written scripts, which use a single forward slash (/). For example, to set the default host to CScript, disable the logo, and save the options for the current user, type the following command at a command prompt:
cscript //h:cscript //nologo //s
After setting these defaults, you no longer have to type the cscript command before running scripts at the command line, and the Microsoft copyright notice isn't shown. I generally recommend using these settings because lots of scripts (including many of the administrative scripts provided by Microsoft) require the CScript host. Also, some properties of the WScript object (not to be confused with the WScript host) exist only when CScript is the active host.
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