IF ERRORLEVEL is a special syntax supported since the DOS days, the %ERRORLEVEL% variable support was added in WinNT.

The original syntax is used like this:

call someapp.exe
if errorlevel 1 goto handleerror1orhigher
if errorlevel 0 echo succuess...

To use the variable, use the normal IF syntax: if %errorlevel%==0 echo success...

Note that %errorlevel% stops working if someone does set errorlevel=foo and it might not get updated for internal cmd.exe commands.

An alternative solution is to use &&:

call someapp.exe && (echo success) || (echo error!)

File “Date modified” property are not updating while modifying a file without closing it.

These days, we are monitoring this issue:
when one was developing a utility that monitors log files as they are updated.

On 2003, opening the log file folder in explorer, you can see the timestamp and files size change before your eyes each time the log is updated.

On 2008, “Last Modified” field on log files is not updated unless another program attempts to open the file or the utility is stopped, even if F5 is pressed to refresh the view.

Explorer gets is information from NTFS, by using a cmd prompt and “dir” we found that the NTFS metadata for the files is not updated until the handle to a file is closed.

Refreshing the information of a FOLDER is just going to go to the (memory resident) metadata cached by NTFS, but querying the file explicitly will force disk I/O to get the properties – this was a design change introduced in Vista to reduce unnecessary disk I/O to improve performance

There are some exceptions to this rule:
– in some, but not all, cases a simple “dir filename” is enough to refresh the metadata
– “special” folders may be treated differently, such as user profiles where we do not expect a large number of files and want to be able to rely on the file data presented
– kernel filter drivers may change the behaviour as by design they “add, remove or
change functionality of other drivers”

As the workaround is for any process to open and close a handle to the log files, a tool was written to do exactly that, plus get the file information, using the following APIs:


Environment Variables

Every process has an environment block that contains a set of environment variables and their values. There are two types of environment variables: user environment variables (set for each user) and system environment variables (set for everyone).

By default, a child process inherits the environment variables of its parent process. Programs started by the command processor inherit the command processor’s environment variables. To specify a different environment for a child process, create a new environment block and pass a pointer to it as a parameter to the CreateProcess function.

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The ‘Sysnative’ folder in 64-bit Windows explained

In this article we explained that in a 64-bit Windows the System32 folder is intended for 64-bit binary files (DLL files etc.) and the SysWOW64 folder is intended for 32-bit binary files. In the article we also explained that if a 32-bit application includes the “\System32” folder name in a folder path, the system automatically makes a redirection to the SysWOW64 folder. This is to prevent compatibility problems when applications are compiled to 64-bit executables.

Continue reading “The ‘Sysnative’ folder in 64-bit Windows explained”

Efficient Windows PowerShell Administration with WMI and CIM

Timothy Warner, author of Sams Teach Yourself Windows PowerShell in 24 Hours, differentiates between the often-confused terms WMI and CIM, and explains how best to use these technologies with Windows PowerShell.

Let’s imagine that you and I started a business manufacturing and selling network interface cards (NICs). Industry standards would be pretty important to us, right? How could we make it easier for our Ethernet NICs to work natively with systems based on, say, Windows, Linux, and OS X? What about compatibility with different network architectures, protocols, and client/server applications? (Whoa-I’m glad we don’t really need to worry about that particular set of problems!)
Continue reading “Efficient Windows PowerShell Administration with WMI and CIM”

What does PowerShell’s [CmdletBinding()] Do?

It’s not unusual to see folks write PowerShell scripts and functions whose first line is [CmdletBinding()]. What’s it do?

It’s generally a big part of advanced functions, or what some folks call “script cmdlets.” Basically, it turns on cmdlet-style parameter binding capabilities, either for a script or for a function. You really get four magical capabilities with it:

  • The ability to add [Parameter()] decorators to parameters – see “about_functions_advanced_parameters” in PowerShell for more detail. Technically, these can be used without adding [CmdletBinding()], but you almost always see them together.
  • The ability to use Write-Verbose and Write-Debug in your script or function, and have their output controlled by -Verbose and -Debug parameters of that script or function. You don’t need to declare those parameters – [CmdletBinding()] adds them.
  • Your script or function picks up the other common parameters, too, like -EV and -EA (see “about_common_parameters”)
  • The ability to have -whatif and -confirm added to your script or function, by specifying something like [CmdletBinding(SupportsShouldProcess=$True,ConfirmImpact=Medium)]. You still have to implement support for these switches by using $pscmdlet.ShouldProcess() in your script.

Unblock a file with PowerShell?

If you are using PowerShell v3, you can use the Unblock-File cmdlet.

The “blocking” part is simply an alternate data stream of the file, named “Zone.Identifier”. You can display it in CMD by using input redirection (no other way to get to a stream in CMD, though):

H:\Downloads> more < test.exe:Zone.Identifier

You can find them using dir /r on Windows Vista and later:

2009-10-24  12:18        54.538.056 test.exe
                                 24 test.exe:Zone.Identifier:$DATA

Also in CMD you can easily get rid of that by overwriting it (using output redirection, this time):


which isn’t quite the same as removing the ADS completely, but works in that Explorer doesn’t complain anymore.

There doesn’t seem to be native support for handling ADS from within PowerShell (as mentioned on The PowerShell Guy’s blog here. That article also has some information how to get that functionality in PowerShell). You could, however, simply call cmd:

cmd /c "echo.>test.exe:Zone.Identifier"

That works from PowerShell as well.

Another option would be Mark Russinovich’s streams utility which allows you to inspect a file’s ADS and also to delete them. So

streams -d myDownloadedFile.exe

does work as well.

Variable scoping in PowerShell

ou can use scope modifiers or the *-Variable cmdlets.

The scope modifiers are:

    • global used to access/modify at the outermost scope (eg. the interactive shell)
    • script used on access/modify at the scope of the running script (.ps1 file). If not running a script then operates as global.


(For the -Scope parameter of the *-Variable cmdlets see the help.)

Eg. in your second example, to directly modify the global $array:

& {
  $global:array +="s"
  Write-Host $array

For more details see the help topic about_scopes.

Log4net tutorial – Great library for logging

log4net tutorial– Great library for logging

A lot of applications use logging as a way to store information about performed operations. Such data is very useful when you have to diagnose an issue. Logging could be done on many ways, but sometimes it’s just easier to use an existing solution. I’d like to introduce one of many libraries for logging, but quite powerful – log4net.

Get log4net

Let’s create a console application – log4netTutorial. Next you have to reference log4net library. The easiest way is to install NuGet package:

    • Right click your project
    • Click Manage NuGet Packages…
    • Click Online on the left hand panel
    • Type log4net in search box on the right side
    • Select log4net package and click Install

Continue reading “Log4net tutorial – Great library for logging”