Public/Watch-Command.ps1
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Function Watch-Command { <# .SYNOPSIS Runs a scriptblock or the preceeding pipeline repeatedly until there is change. .DESCRIPTION The Watch-Command cmdlet runs a specified scriptblock repeatedly at the specified interval (or every 1 second by default) and returns the result of the scriptblock when the output has changed. For the command to work the specified scriptblock must return a result to the pipeline. .PARAMETER ScriptBlock The scriptblock to execute, specified via curly braces. If you provide input via the pipleine that isn't a scriptblock then the entire invocation line that preceeded the cmdlet will be used as the scriptblock input. .PARAMETER Seconds Number of seconds to wait between checks. Default = 1 .PARAMETER Difference Switch: Use to only output items in the collection that have changed dditions or modifications). .PARAMETER Continuous Switch: Run continuously (even after a change has occurred) until exited with CTRL+C. .PARAMETER AsString Switch: Converts the result of the scriptblock into an array of strings for comparison. .PARAMETER ClearScreen Switch: Clears the screen between each different result. You can also use 'cls' as an alias. .PARAMETER PassThru Switch: Passes through the initial result from the command (before any change has occurred). .PARAMETER Property Manually specify one or more property names to be used for comparison. If not specified, the default display property set is used. If there is not a default display property set, all properties are used. You can also use '*' to force all properties. .EXAMPLE Watch-Command -ScriptBlock { Get-Process } Runs Get-Process and waits for any returns the result when the data has changed. .EXAMPLE Get-Service | Watch-Command -Diff -Cont Runs Get-Service and returns any differences in the resultant data, continuously until interrupted by CTRL+C. .EXAMPLE Watch-Command { Get-Content test.txt } -Difference -Verbose -ClearScreen Uses Get-Content to monitor test.txt. Shows any changes and clears the screen between changes. .EXAMPLE Get-ChildItem | Watch-Command -Difference -AsString Monitors the result of GEt-ChildItem for changes, returns any differences. Treats the input as strings not objects. .EXAMPLE Get-Process | Watch-Command -Difference -Property processname,id -Continuous Monitors Get-Process for differences in the specified properties only, continues until interrupted by CTRL+C. #> [cmdletbinding()] Param( [parameter(ValueFromPipeline, Mandatory)] [object] $ScriptBlock, [int] $Seconds = 1, [switch] $Difference, [switch] $Continuous, [switch] $AsString, [alias('cls')] [switch] $ClearScreen, [switch] $PassThru, [string[]] $Property ) if ($ScriptBlock -isnot [scriptblock]) { if ($MyInvocation.PipelinePosition -gt 1) { $ScriptBlock = [Scriptblock]::Create( ($MyInvocation.Line -Split "\|\s*$($MyInvocation.InvocationName)")[0] ) } else { Throw 'The -ScriptBlock parameter must be provided an object of type ScriptBlock unless invoked via the Pipeline.' } } Write-Verbose "Started executing $($ScriptBlock | Out-String)" $FirstResult = Invoke-Command $ScriptBlock if ($AsString) { $FirstResult = $FirstResult | Out-String -Stream } elseif (($FirstResult | Select-Object -First 1) -isnot [string]){ if (-not $Property) { $Property = ($FirstResult | Select-Object -First 1).PSStandardMembers.DefaultDisplayPropertySet.ReferencedPropertyNames } if (-not $Property -or $Property -eq '*') { $Property = ($FirstResult | Select-Object -First 1).PSObject.Properties.Name } Write-Verbose "Watched properties: $($Property -Join ',')" } if ($PassThru) { if ($ClearScreen) { Clear-Host } Write-Output $FirstResult } do { do { if ($Result) { Start-Sleep $Seconds } $Result = Invoke-Command $ScriptBlock if ($AsString) { $Result = $Result | Out-String -Stream } $CompareParams = @{ ReferenceObject = @($FirstResult | Select-Object) DifferenceObject = @($Result | Select-Object) } if ($Property) { $CompareParams.Add('Property', $Property) } $Diff = Compare-Object @CompareParams -PassThru } until ($Diff) if ($ClearScreen) { Clear-Host } Write-Verbose "Change occurred at $(Get-Date)" if ($Difference) { $Diff | Where-Object {$_.SideIndicator -eq '=>'} } else { $Result } $FirstResult = $Result } until (-not $Continuous) } |