Input Output Streams

Overview

Even with the graphical user interface, command-line console applications are still important, especially when mass repetitive changes are required that would take a great amount of time to perform through the graphical user interface or when scripts are designed to perform operations that do not require user interaction.

Windows Script Host (WSH) 1.0 allowed the processing of command-line parameters. WSH version 2.0 introduces the ability to process standard input and output streams (StdIn and StdOut). This new feature is of great importance for the creation of flexible console applications.

The command-line environment has always supported the capability of "piping" streams from one console application to another, but it has never provided a great number of built-in commands to use this ability, apart from the MORE and SORT commands.

This capability has always been an important feature in the UNIX environment, and most native UNIX shell commands allow (or require) input to be provided via standard input, allowing complex sequences of operations to be executed within a single command line.

Using Regular Expressions to Filter the Contents of an Input Stream

Problem

You require a routine that filters supplied information and then outputs any results that meet the criteria to the standard output (StdOut). The resulting output can be used by other console applications.

Solution

The following script reads input from standard input using the WScript.StdIn object, and then it filters the line against a regular expression. Only lines that match the expression are written to standard output:

Discussion

WSH version 2.0 provides access to the standard input and outputs (StdIn and StdOut) from the Windows console. This allows scripts to "pipe" information between console applications.

Piping allows for information to be passed from one console application to another. Using the vertical bar (|) pipes information between one or more console applications. For example:

dir /b | sort | more

To access the StdIn or StdOut stream, use the StdIn and StdOut property of the WScript object. These properties return TextStream objects that can be read and written to as if they were text files. For example, the following WSH script reads a line from the standard input and writes its uppercase equivalent to the standard output by using the StdIn and StdOut properties:

'ucasein.vbs 'converts standard Input stream to uppercase 'and redirects to stdout Dim strText strText = WScript.StdIn.ReadAll WScript.StdOut.Write Ucase(strText)

To use the ucasein script, pipe output to it from other applications. The following command-line snippet pipes the file users.txt to the script:

cscript ucasein.vbs < users.txt > ucusers.txt

The contents of the input stream (in this case, users.txt) is converted to uppercase and written to standard output. The standard output in this case is redirected to a new file: ucusers.txt. Information can be piped to a WSH script from any existing console application or other scripts that write information to the StdOut stream.

If you execute a console script that reads StdIn but does not have information piped from another application or from a file, the application will take input from the user's standard input device, the keyboard. In this case, the script will pause to accept keyboard input. The following command line starts the ucasein script and accepts input from the keyboard because no other source is redirected/piped to the script:

cscript ucasein.vbs

Press Ctrl-Z to end the processing of keyboard input from StdIn. This key-stroke combination sends an end of file (EOF) sequence to the stream. Pressing Ctrl-Break when reading keyboard input from StdIn will force an EOF.

To pipe information to a WSH script, execute a console application and pipe the output to the WSH script. The following script pipes the contents of a dir command to the ucasein script:

dir | cscript ucasein.vbs | more

The output of the dir command is converted to uppercase. This result is then piped to the more command, which displays one screen of text at a time.

When you chain commands together on non-Windows 2000/XP machines, the script must be prefixed by Cscript or Wscript. The following command line is the equivalent of the previous sample:

dir | ucasein.vbs | more

This generates an error when run on Windows NT 4.0/9x/ME computers. On Windows 2000/XP, it will use the default script host, either Cscript or Wscript. If a script writes to StdOut, you should use Cscript because if the result of the out-put is not piped to another process, an error will occur. The following example will not work:

dir | wscript ucasein.vbs

The preceding example doesn't work because the results are not piped to another process and the Wscript script host does use the results. Replacing Cscript with Wscript in the example would result in the output being displayed in the console. The earlier example in which the results were piped to the more command would work using Wscript.

Even though you can use Wscript to execute scripts that use StdIn, you should avoid using it to write to StdOut.

The Solution script evaluates each line on the StdIn against a regular expression. Any resulting matches are written to StdOut. For example, say you want to output the routing tables to a file without any of the additional headings:

route print | cscript //NoLogo wshgrep.wsf (d+.d+.d+.d.+){4} > rt.txt

The Route Print command pipes the routing information to the wshgrep.wsf script. WshGrep filters out all lines that meet the criteria and outputs them to StdOut. This output is redirected to the file rt.txt.

The //Nologo switch ensures that no "logo" information from the execution of the script appears with the output. This includes the Microsoft WSH version and copyright information.

If you want to prevent the display of the Microsoft logo and copyright information by default, use the //S switch to save the command-line settings as the default:

wscript //NoLogo //S

This saves the //NoLogo switch as a default switch.

The wshgrep.wsf script and other scripts in this section include an fsolib.vbs script library to implement repetitive functions. The fsolib.vbs script library is shown here:

'fsolib.vbs 'Description: Contains routines used by FSO scripts 'check if script is being run interactively 'Returns:True if run from command line, otherwise false Function IsCscript() IsCScript = (StrComp(Right(WScript.Fullname,11)," cscript.exe",1) = 0) End Function 'display an error message and exist script 'Parameters: 'strMsg Message to display 'strUseWscript Use Wscript.Echo to display message. ' By default StdErr is used, but this cannot be used in ' interactive (wscript) mode unless redirected to somewhere else. Sub ExitScript(strMsg, bUseWscript) If bUseWscript Then WScript.Echo strMsg Else 'get the standard error stream WScript.StdErr.WriteLine strMsg End If WScript.Quit -1 End Sub 'returns contents of specified file. If file doesn't exist 'terminates script and displays error message 'Parameters: 'strFile Path to file to return 'Returns 'contents of specified file Function GetFile(strFile) On Error Resume Next Dim objFSO, objFile Set objFSO = CreateObject("Scripting.FileSystemObject") Set objFile = objFSO.OpenTextFile(strFile) If Err Then ExitScript _ "Error "& Err.Description & "opening file "& _ strFile, False GetFile = objFile.ReadAll objFile.Close End Function 'terminates script with message if script not run using cscript.ext 'Parameters:None Sub CheckCScript() If Not IsCscript Then ExitScript _ "This script must be run from command line using cscript.exe", True End Sub 'checks if specified number of arguments have been passed and exits script 'displaying usage information if not 'Parameters: 'nCount Number of arguments expected Sub CheckArguments(nCount) If WScript.Arguments.Count <> nCount Then WScript.Arguments.ShowUsage WScript.Quit End If End Sub

See Also

Solution 3.1 and Solution 8.1.

Reading Keyboard Input

Problem

You want to create a simple text-based menu.

Solution

You can read a character from standard input using the Read method:

Discussion

Even though Windows provides an advanced graphical user interface, it can still be useful to provide text-based menus for console applications. StdIn provides a method of reading input from the console.

If no stream is redirected to StdIn, the keyboard is used to read StdIn. StdIn returns a TextStream object and supports the methods provided through this object to read input (Read, ReadLine, and ReadAll methods).

Using the Read method, you can specify the number of characters you want to read. The method does not terminate once the number of characters specified has been entered; you must press the Enter key or the EOF key combination (Ctrl-Z). Only the number of characters specified by the Read method is actually returned.

See Also

Solution 3.2.

Generating Template Based Data

Problem

You want to be able to search and replace values from standard input.

Solution

You can read the standard input stream using WScript.StdIn and then use the results to populate templates that are provided through a command-line parameter or external file:

Out.txt Suppose Replacements.txt contained Bob,*.doc Sue,*.txt and Template.txt contained net use \odin /user:admin /password:bigsecret copy \odinackmeup \lokiackups net use /d \odin then Out.txt would contain net use \odinob /user:admin /password:bigsecret copy \odinobackmeup*.doc \lokiackupsob net use /d \odinob net use \odinsue /user:admin /password:bigsecret copy \odinsueackmeup*.txt \lokiackupssue net use /d \odinsue ]]>

Discussion

The search and replace script creates output in which tags in a template string are replaced by elements from standard input.

Each line of the standard input must consist of data elements delimited by a comma. These elements are identified by their ordinal position in the line, so the first element is 1, the second element is 2, and so on.

The following users.txt text file contains information that can be piped to the script. In this example, there are three elements for each line:

Freds,Fred Smith,Accounting Manager Joeb,Joe Blow,Computer Operator

The template string can either be a text file or a command-line parameter. In the template, any instance of an element number surrounded by is replaced by the first element from standard input, with the second, and so on:

net user password /ADD /FULLNAME:"" /COMMENT:""

Using first line of users.txt as input, the following output is generated:

net user password Freds /ADD /FULLNAME:" Fred Smith" /COMMENT:" Accounting Manager" net user password Joeb /ADD /FULLNAME:" Joe Blow" /COMMENT:" Computer Operator"

To run the users.txt file against a layout string and redirect the output to a batch file called newusers.bat, use the following:

cscript sar.wsf template.txt < users.txt > newusers.bat

The sar script processes each line of the standard input for data. You can use this ability to use the search and replace script to fill in a template with data as a very flexible tool for creating formatted output. For example, suppose that you want to take the list of users from a text file and generate an HTML file containing the user list in a table. The following layout file, details.txt, contains the template table details for each user:

With this template, you can generate the HTML table details using the users.txt file:

cscript sar.wsf details.txt < users.txt

However, to create a complete HTML document, you need to include the appropriate HTML

,

, and elements to surround the detail lines. You can't use the sar.wsf script to insert the details into the body because it processes line by line and would generate an unusable HTML document. You require results of the table generation to be inserted into the body of an HTML document.

To do this, create a modified version of the sar.wsf script called sarw.wsf to treat the standard input as one element to be replaced in a template:

Out.txt Suppose Replacements.txt contained Fred Smith 555-1234 Joe Blow 555-2432 and Template.txt contained Phone List Name Phone then Out.txt would contain: Phone List Name Phone Fred Smith 555-1234 Joe Blow 555-2432 ]]>

The sarw.wsf script replaces the element in a template file with the StdIn contents and writes the results to StdOut. The following template file, body.txt, is used to generate the body of the HTML file:

The following command sequence generates the HTML file usrs.htm using the details.txt and body.txt templates:

cscript sar.wsf details.txt < users.txt | cscript sarw.wsf body.txt > usrs.htm

The resulting output is similar to this:

The first step redirects the users.txt file to sar.wsf, which generates the HTML table details. The result of this operation is piped to sarw.wsf, which inserts it into the body.txt template. The result of this operation is redirected to the usrs.htm file.

6 4 Creating Multiple User Prompts

Problem

Existing data files usually provide the standard input that scripts read. This is useful when processing multiple items, but it can be a bit impractical for single pieces of information. You want to be able to query the user with one or more predefined prompts and then take the results and send them to the standard output.

Solution

You can use the StdErr output stream to prompt users for information, which is then piped to standard output for further processing. Using StdErr instead of StdOut to output information ensures that the user prompts do not get piped with the user input results.

Discussion

The prompt.wsf script queries the user for input with prompts that are defined by a template file. This allows the script to prompt the user for information that is piped or redirected to another process, and it provides an alternative to building data files to redirect to scripts.

You use the script to create a solution that builds a batch file to create a new NT user by prompting for user details. The following nusr.txt file contains the prompts to create a new user:

Enter user id: Enter user full name Enter comment:

Each prompt appears on its own line in the file. You now need a template file to fill in the user details. Use the sar.wsf script from Solution 6.3 to insert the prompts into a template. The following text file contains the layout for the nuser.txt template:

rem nuser.txt Rem create user net user /ADD Rem create a user directoryMd d:users rem Create the share net share $=d:users rem Grant and Domain Admins full access to the share rem shrperm is part of Backoffice resource kit shrperm \Odin$ :F "Domain Admins":F rem Grant user full access to his or her directory cacls d:users /T /E /G :F rem Remove Everyone access from directory cacls d:users /T /E /R Everyone remPermit Domain Admins to have full access in directory. cacls d:users /T /E /P "Domain admins":F rem set the home directory setting for user net user /HOMEDIR:\Odin$ net user /FULLNAME:"" net user /COMMENT:""

The following command line uses prompt.wsf to prompt for a user ID, description, and comment:

cscript prompt.wsf inp.txt | cscript sar.wsf nuser.txt > nuser.bat

Next, this information is piped to the sar.wsf script, which builds the nuser.bat batch file using the nuser.txt template file.

The prompt.wsf script generates user prompts from a file. These prompts are displayed using the StdErr stream. The standard error (StdErr) output stream is used to display the prompts. Functionally, StdErr appears similar to StdOut. It returns a TextStream object and any output written to it appears on the console.

The difference is that anything written to the StdErr stream is not available to be read by the StdIn stream. The purpose of the StdErr stream is to display error messages in console scripts that perform StdIn/StdOut operations. This behavior is used by prompt.wsf to display the prompts. If StdOut or WScript.Echo had been used, the prompts would be piped with the results of user prompts.

See Also

Solution 3.8 and Solution 3.9 .

Chapter 7 Registry Operations