Select-String -Context
A lot of people use Select-String but I haven’t seen much discussion of the –Context parameter. This is an awesome feature that we added in V2. If you haven’t tried it, you should spend a few minutes experimenting. I can guarantee you that will you be glad you did.
Let’s see what the HELP has to say about the Context parameter:
PS> Get-Help Select-String -Parameter Context
-Context <Int32[]>
Captures the specified number of lines before and after the line with the m
atch. This allows you to view the match in context.
If you enter one number as the value of this parameter, that number determi
nes the number of lines captured before and after the match. If you enter t
wo numbers as the value, the first number determines the number of lines be
fore the match and the second number determines the number of lines after t
he match.
In the default display, lines with a match are indicated by a right angle b
racket (ASCII 62) in the first column of the display. Unmarked lines are th
e context.
This parameter does not change the number of objects generated by Select-St
ring. Select-String generates one MatchInfo (Microsoft.PowerShell.Commands.
MatchInfo) object for each match. The context is stored as an array of stri
ngs in the Context property of the object.
When you pipe the output of a Select-String command to another Select-Strin
g command, the receiving command searches only the text in the matched line
(the value of the Line property of the MatchInfo object), not the text in
the context lines. As a result, the Context parameter is not valid on the r
eceiving Select-String command.
When the context includes a match, the MatchInfo object for each match incl
udes all of the context lines, but the overlapping lines appear only once i
n the display.
Required? false
Position? named
Default value
Accept pipeline input? false
Accept wildcard characters? false
Let’s have some fun. I’m going to use Superstar James O’Neil’s Hypervisor Management Library to experiment with. He has a number of functions the work with NICs. Let’s party.
PS> #First Let’s find the functions
PS> dir *.ps1 |Select-String function.*NIC
network.ps1:3:Function Add-VMNIC
network.ps1:64:Function Get-VMNic
network.ps1:94:Function Get-VMNicport
network.ps1:104:Function Get-VMnicSwitch
network.ps1:121:Function Get-VMNICVLAN
network.ps1:282:Function Remove-VMNIC
network.ps1:332:Function remove-VMSwitchNIC
network.ps1:366:Function Select-VMNIC
network.ps1:392:Function Set-VMNICAddress
network.ps1:422:Function Set-VMNICSwitch
network.ps1:459:Function Set-VMNICVLAN
PS> # That gave me too many so let’s add a $ to the end of the SEARCH STRING
PS> # That indicates a Line end
PS> dir *.ps1 |Select-String function.*NIC$
network.ps1:3:Function Add-VMNIC
network.ps1:64:Function Get-VMNic
network.ps1:282:Function Remove-VMNIC
network.ps1:366:Function Select-VMNIC
PS> # Let’s see 1 line before and after each matching line
PS> dir *.ps1 |Select-String function.*NIC$ -Context 1
network.ps1:2:
> network.ps1:3:Function Add-VMNIC
network.ps1:4:{# .ExternalHelp MAML-VMNetwork.XML
network.ps1:63:
> network.ps1:64:Function Get-VMNic
network.ps1:65:{# .ExternalHelp MAML-VMNetwork.XML
network.ps1:281:
> network.ps1:282:Function Remove-VMNIC
network.ps1:283:{# .ExternalHelp MAML-VMNetwork.XML
network.ps1:365:
> network.ps1:366:Function Select-VMNIC
network.ps1:367:{# .ExternalHelp MAML-VMNetwork.XML
PS> # Notice the line numbers and that the matching line has a > in front
PS> # Now let’s try 3 lines before and after the matching line
PS> dir *.ps1 |Select-String function.*NIC$ -Context 3
network.ps1:1:
network.ps1:2:
> network.ps1:3:Function Add-VMNIC
network.ps1:4:{# .ExternalHelp MAML-VMNetwork.XML
network.ps1:5: [CmdletBinding(SupportsShouldProcess=$true)]
network.ps1:6: param(
network.ps1:61:}
network.ps1:62:
network.ps1:63:
> network.ps1:64:Function Get-VMNic
network.ps1:65:{# .ExternalHelp MAML-VMNetwork.XML
network.ps1:66: param(
network.ps1:67: [parameter(ValueFromPipeline = $true)]
network.ps1:279:}
network.ps1:280:
network.ps1:281:
> network.ps1:282:Function Remove-VMNIC
network.ps1:283:{# .ExternalHelp MAML-VMNetwork.XML
network.ps1:284: [CmdletBinding(SupportsShouldProcess=$true)]
network.ps1:285: param(
network.ps1:363:
network.ps1:364:
network.ps1:365:
> network.ps1:366:Function Select-VMNIC
network.ps1:367:{# .ExternalHelp MAML-VMNetwork.XML
network.ps1:368: param(
network.ps1:369: [parameter(ValueFromPipeline = $true)]
PS> # The line before is boring so let’s get rid of that and then see a
PS> # few lines after
PS> dir *.ps1 |Select-String function.*NIC$ -Context 0,3
> network.ps1:3:Function Add-VMNIC
network.ps1:4:{# .ExternalHelp MAML-VMNetwork.XML
network.ps1:5: [CmdletBinding(SupportsShouldProcess=$true)]
network.ps1:6: param(
> network.ps1:64:Function Get-VMNic
network.ps1:65:{# .ExternalHelp MAML-VMNetwork.XML
network.ps1:66: param(
network.ps1:67: [parameter(ValueFromPipeline = $true)]
> network.ps1:282:Function Remove-VMNIC
network.ps1:283:{# .ExternalHelp MAML-VMNetwork.XML
network.ps1:284: [CmdletBinding(SupportsShouldProcess=$true)]
network.ps1:285: param(
> network.ps1:366:Function Select-VMNIC
network.ps1:367:{# .ExternalHelp MAML-VMNetwork.XML
network.ps1:368: param(
network.ps1:369: [parameter(ValueFromPipeline = $true)]
PS> # Let’s take a look at the body of Remove-VMNIC
PS> dir *.ps1 |Select-String function.*Remove-VMNIC$ -Context 0,20
> network.ps1:282:Function Remove-VMNIC
network.ps1:283:{# .ExternalHelp MAML-VMNetwork.XML
network.ps1:284: [CmdletBinding(SupportsShouldProcess=$true)]
network.ps1:285: param(
network.ps1:286: [parameter(Mandatory = $true , ValueFromPipeline = $true)]
network.ps1:287: $Nic,
network.ps1:288:
network.ps1:289: $PSC,
network.ps1:290: [switch]$force,
network.ps1:291:
network.ps1:292: $VM, $Server #VM no longer required, but preserved for compatibility with V1
network.ps1:293: )
network.ps1:294: process {
network.ps1:295: if ($psc -eq $null) {$psc = $pscmdlet} ; if (-not $PSBoundParameters.psc) {$PSBoundParameter
s.add("psc",$psc)}
network.ps1:296: if ($NIC -is [Array] ) {[Void]$PSBoundParameters.Remove("NIC") ; $NIC | ForEach-object {Remo
ve-VMNIC -NIC $_ @PSBoundParameters}}
network.ps1:297: if ($nic -is [System.Management.ManagementObject]) {remove-VMRasd -rasd $NIC -PSC $psc }
network.ps1:298: # note: In V1 the switch port was removed before removing the NIC, but this is done autom
atically.
network.ps1:299: }
network.ps1:300:}
network.ps1:301:
network.ps1:302:
Party on your own. You are going to love –Context!
Experiment! Enjoy! Engage!
Jeffrey Snover [MSFT]
Distinguished Engineer
Visit the Windows PowerShell Team blog at: http://blogs.msdn.com/PowerShell
Visit the Windows PowerShell ScriptCenter at: http://www.microsoft.com/technet/scriptcenter/hubs/msh.mspx
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