Power Tips

Converting TABs to Spaces

ps1 — Fri, 03 Feb 2012 12:00:00 GMT

When you want to publish PowerShell code, you may want to make sure that all TAB characters are converted to one or more spaces to save space.

Here's the code that turns TAB characters to spaces:

PS> $text = "This is a`tTAB-delimited`tText"
PS> $text
This is a       TAB-delimited   Text
PS> $text -replace '\t', '  '
This is a  TAB-delimited  Text

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Removing Multiple White Spaces

ps1 — Thu, 02 Feb 2012 12:00:00 GMT

Removing multiple white spaces from text is easy in PowerShell. Simply use -replace operator and look for whitespaces ("\s") that occur one or more time ("+"), then replace them all with just one whitespace:

PS> '[     Man,     it works!     ]' -replace '\s+', ' '
[ Man, it works! ]

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Removing Options from Command String (Enhancement)

ps1 — Wed, 01 Feb 2012 12:00:00 GMT

In a previous tip we showed how you can remove options from a command line text using -replace. Here is a more versatile approach. It will remove any character or word that starts with "/" and then remove all trailing spaces as well:

PS> $command = 'somecommand "C:\Some Folder" "C:\Some New Folder Name" /y /r /quiet /simple'
PS> ($command -replace '/\w*', $null).trim()
somecommand "C:\Some Folder" "C:\Some New Folder Name"

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Remove Options from Command String

ps1 — Tue, 31 Jan 2012 12:00:00 GMT

Let's assume you'd like to remove all options from a raw text command such as this one:

xcopy "C:\Some Folder" "C:\Some New Folder Name" /y /r /Q

Since all options start with "/" and are a single character, you can derive a pattern and use a regular expression replace operation. Have a look:

PS> 'xcopy "C:\Some Folder" "C:\Some New Folder Name" /y /r /Q' -replace '/.', $null
xcopy "C:\Some Folder" "C:\Some New Folder Name"

All options are removed. -replace was looking for a "/" and then any other character (".") and replacing every occurrence with nothing ($null).

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Using Shared Variables

ps1 — Mon, 30 Jan 2012 12:00:00 GMT

By default, all variables created in functions are local, so they only exist within that function and all functions that are called from within this function.

Sometimes, you'd like to examine variables defined in a function after that function executed. Or you'd like to persist a variable, so next time the function is called it can increment some counter or continue to work with that variable rather than creating a brand new variable each time.

To achieve this, use shared variables by prepending 'Script:' to a variable name. Here's a sample:

PS> function Call-Me { $script:counter ++; "You called me $script:counter times!" }
PS> Call-Me
You called me 1 times!
PS> Call-Me
You called me 2 times!
PS> Call-Me
You called me 3 times!

Note that the variable $counter now does not exist inside the function anymore. Instead, it is created in the context of the caller (the place where you called Call-Me). If you prepended a variable name with 'global:', the variable would be created in the topmost context and thus available everywhere.

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Catching Errors

ps1 — Fri, 27 Jan 2012 12:00:00 GMT

In forums, people often get confused with error handling. For example, this code does not call the error handler. Instead, the red PowerShell error message pops up:

try { Remove-Item \\$name\c$\windows\temp\filename.exe }
catch {Write "Not able to access files on $name"}

When you want to catch errors produced by cmdlets, always make sure you add the parameter -ErrorAction Stop to it. Only then will the cmdlet emit an exception that your script can handle. So this works:

try { Remove-Item \\$name\c$\windows\temp\filename.exe -ErrorAction Stop }
catch {Write "Not able to access files on $name"}

If you want error handling for all cmdlets, you can also change the default mode like this:

$ErrorActionPreference = 'Stop'

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Analyzing System Restarts (Alternative)

ps1 — Thu, 26 Jan 2012 12:00:00 GMT

In a previous tip we showed how to use Get-EventLog to extract all events related to system reboots. In PowerShell v2, a new cmdlet called Get-WinEvent was added. With it, you can not only access and read the "classic" event logs but also the application event logs introduced in Windows Vista.

To illustrate this, here's sample code that uses Get-WinEvent to extract reboot events:

Get-WinEvent -FilterHashtable @{logname='System'; id=1074}  |
  ForEach-Object {
    $rv = New-Object PSObject | Select-Object Date, User, Action, process, Reason, ReasonCode, Comment
    $rv.Date = $_.TimeCreated
    $rv.User = $_.Properties[6].Value
    $rv.Process = $_.Properties[0].Value
    $rv.Action = $_.Properties[4].Value
    $rv.Reason = $_.Properties[2].Value
    $rv.ReasonCode = $_.Properties[3].Value
    $rv.Comment = $_.Properties[5].Value
    $rv
    
  } | Select-Object Date, Action, Reason, User

Note that Get-WinEvent will not work with Windows XP.

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Analyzing System Restarts

ps1 — Wed, 25 Jan 2012 12:00:00 GMT

To find out when a system restarted and why, use the below code to extract the relevant information from the System event log:

Get-EventLog -LogName System -ComputerName storage1 |
where {$_.EventId -eq 1074} |
ForEach-Object {

    $rv = New-Object PSObject | Select-Object Date, User, Action, process, Reason, ReasonCode, Comment, Message
    if ($_.ReplacementStrings[4]) {
        $rv.Date = $_.TimeGenerated
        $rv.User = $_.ReplacementStrings[6]
        $rv.Process = $_.ReplacementStrings[0]
        $rv.Action = $_.ReplacementStrings[4]
        $rv.Reason = $_.ReplacementStrings[2]
        $rv.ReasonCode = $_.ReplacementStrings[3]
        $rv.Comment = $_.ReplacementStrings[5]
        $rv.Message = $_.Message
        $rv
    }
} | Select-Object Date, Action, Reason, User

Event ID 1074 represents a restart event. Rather than extracting the relevant information from the event message text, this code uses the ReplacementStrings property which is an array and holds the significant information bits. Accessing the event entries' replacement strings is much easier than parsing the message text.

The code returns information only if the particular event entry has content in ReplacementStrings[4] (the 5th element of the array) because only then does the event entry represent a shutdown or reboot event.

Note that Get-EventLog supports the -ComputerName parameter, so if a remote system is set up for remote access and you own the appropriate privileges, you can also analyze remote systems.

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Sending Emails Securely (via SSL)

ps1 — Tue, 24 Jan 2012 12:00:00 GMT

In a previous tip we showed how to use the Send-MailMessage cmdlet to send off emails and preserve special characters by using UTF8 encoding. When you try this with your freemailer, you may run into issues where your SMTP server complains about needing a secure connection.

So, when you receive such an error message, make sure you add the switch parameter -UseSsl. This only works right though if you use PowerShell v3 (the public CTP2 is readily available). In PowerShell v2, Send-MailMessage does not use the correct port for SSL connections.

Here is a sample that uses the live.com freemailer (formally called "Hotmail") which does require a secure connection:

PS> Send-MailMessage -Body 'My mail message can contain special characters: äöüß' -From youraccountname@hotmail.com -to someone@somewhere.com -Credential youraccountname@hotmail.com -SmtpServer smtp.live.com -Subject 'Sending Mail from PowerShell' -Encoding UTF8 -UseSsl

Note that PowerShell v3 Send-MailMessage accepts "UTF8" directly so you no longer need to submit the awkward ([System.Text.Encoding]::UTF8).

There are plenty of websites that list SMTP server URLs for your favorite provider: http://www.e-eeasy.com/SMTPServerList.aspx.

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Sending Emails with Special Characters

ps1 — Mon, 23 Jan 2012 12:00:00 GMT

PowerShell has built-in support for sending emails: Send-MailMessage! All you need is an SMTP server. However, with standard encoding you may run into issues where special characters are mangled. Use the -Encoding parameter and specify UTF8 to preserve such characters. Here's a sample with a German freemailer web.de:

Send-MailMessage -Body 'I can send special characters: äöüß' -From youraccountname@web.de -to someone@somewhere.com -Credential (Get-Credential youraccountname@web.de) -SmtpServer smtp.web.de -Subject 'Sending Mail From PowerShell' -Encoding ([System.Text.Encoding]::UTF8)

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Check Active Internet Connection

ps1 — Fri, 20 Jan 2012 12:00:00 GMT

If your machine is connected to the Internet more than once, let's say cabled and wireless at the same time, which connection is used? Here's a function that tells you (thanks for inspiration to fellow MVP Richard Siddaway):

function test-ipmetric {
    Get-WmiObject Win32_NetworkAdapter -Filter "AdapterType='Ethernet 802.3'" |
    ForEach-Object { $_.GetRelated('Win32_NetworkAdapterConfiguration') } |
    Select-Object Description, Index, IPEnabled, IPConnectionMetric
}

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Use WMI and WQL!

ps1 — Thu, 19 Jan 2012 12:00:00 GMT

WMI is a great information resource, and Get-WmiObject makes it easy to retrieve WMI instances. First, use -List parameter to find WMI class names. For example, find classes that deal with network:

Get-WmiObject -List Win32_*network*

Next, pick one of the classes and enumerate its instances:

Get-WmiObject Win32_NetworkAdapterConfiguration

With WQL, a SQL-type query language for WMI, you can even create more sophisticated queries, such as:

Get-WmiObject -Query 'Select * FROM Win32_NetworkAdapterConfiguration WHERE IPEnabled=True'

To learn more about the specific WQL format and the keywords you can use, check this reference: http://msdn.microsoft.com/en-us/library/windows/desktop/aa394606(v=vs.85).aspx

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Convert to Numeric

ps1 — Wed, 18 Jan 2012 12:00:00 GMT

Whenever PowerShell asks for user input or reads text file content, the results are text strings. If you expect numbers and want to calculate, make sure you cast them to a numeric format. Have a look:

PS> $number = Read-Host 'Enter a number'
Enter a number: 100
PS> $number * 12
100100100100100100100100100100100100

Now try the same with casting:

PS> $number = [Double](Read-Host 'Enter a number')
Enter a number: 100
PS> $number * 12
1200

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Read/Delete/Move Every X. File

ps1 — Tue, 17 Jan 2012 05:00:00 GMT

Occasionally, you may want to act on every 2nd or 3rd file in a folder (or line in a file). The easiest way to identify every x. element is to use the "%" (modulus) operator.

This will list every 5th file in the Windows folder (for what it's worth):

PS> Dir $env:windir | ForEach-Object { $x=0 } { $x++; if ($x % 5 -eq 0) { $_ } }

And this would read every 50th line from windowsupdate.log:

PS> Get-Content $env:windir\windowsupdate.log | ForEach-Object { $x=0 } { $x++; if ($x % 50 -eq 0) { $_ } }

It's always the same procedure: ForEach-Object implements a counter in $x, and only if the current counter is dividable by the increment you want (% returns 0) will the object be returned. Now it's just up to you to find use cases for this.

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Managing Internet Cookies

ps1 — Mon, 16 Jan 2012 12:00:00 GMT

Ever wondered what Internet sites store inside cookies when you visit them? This line will dump all cookies:

PS> dir ([system.environment]::GetFolderPath('Cookies'))

Cookies are text files. In older versions of IE, the file name contains the site URL that stored the cookie. To list all cookies from Google, you could try this:

PS> dir ([system.environment]::GetFolderPath('Cookies')) | Where-Object { $_.Name -like '*google*' }

And to actually read the cookie content, simply add Get-Content:

PS> dir ([system.environment]::GetFolderPath('Cookies')) | Where-Object { $_.Name -like '*google*' } | Get-Content

Likewise, by adding Remove-Item you could delete selected or all cookies.

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