Power$nippets

ConvertTo-Expression

Serializes an object to a PowerShell expression

The ConvertTo-Expression cmdlet converts (serializes) an object to a PowerShell expression. The object can be stored in a variable, file or any other common storage for later use or to be ported to another system.

Converting back from an expression

An expression can be restored to an object using the native Invoke-Expression cmdlet:

$Object = Invoke-Expression ($Object | ConverTo-Expression)

Or Converting it to a [ScriptBlock] and invoking it with cmdlets along with Invoke-Command or using the call operator (&):

$Object = &([ScriptBlock]::Create($Object | ConverTo-Expression))

An expression that is stored in a PowerShell (.ps1) file might also be directly invoked by the PowerShell dot-sourcing technique, e.g.:

$Object | ConvertTo-Expression | Out-File .\Expression.ps1
$Object = . .\Expression.ps1

Warning: Invoking partly trusted input with Invoke-Expression or [ScriptBlock]::Create() methods could be abused by malicious code injections.

Examples

Convert a Calendar object to a PowerShell expression:

PS C:\> (Get-UICulture).Calendar | ConvertTo-Expression

[pscustomobject]@{
	'AlgorithmType' = 1
	'CalendarType' = 1
	'Eras' = ,1
	'IsReadOnly' = $False
	'MaxSupportedDateTime' = [datetime]'9999-12-31T23:59:59.9999999'
	'MinSupportedDateTime' = [datetime]'0001-01-01T00:00:00.0000000'
	'TwoDigitYearMax' = 2029
}

PS C:\> (Get-UICulture).Calendar | ConvertTo-Expression -Strong

[pscustomobject]@{
	'AlgorithmType' = [System.Globalization.CalendarAlgorithmType]'SolarCalendar'
	'CalendarType' = [System.Globalization.GregorianCalendarTypes]'Localized'
	'Eras' = [array][int]1
	'IsReadOnly' = [bool]$False
	'MaxSupportedDateTime' = [datetime]'9999-12-31T23:59:59.9999999'
	'MinSupportedDateTime' = [datetime]'0001-01-01T00:00:00.0000000'
	'TwoDigitYearMax' = [int]2029
}

Save an object in a file and to restore it later:

PS C:\>Get-Date | Select-Object -Property * | ConvertTo-Expression | Out-File .\Now.ps1

PS C:\>$Now = .\Now.ps1	# Simular to: $Now = Get-Content .\Now.Ps1 -Raw | Invoke-Expression

PS C:\>$Now

Date        : 1963-10-07 12:00:00 AM
DateTime    : Monday, October 7, 1963 10:47:00 PM
Day         : 7
DayOfWeek   : Monday
DayOfYear   : 280
DisplayHint : DateTime
Hour        : 22
Kind        : Local
Millisecond : 0
Minute      : 22
Month       : 1
Second      : 0
Ticks       : 619388596200000000
TimeOfDay   : 22:47:00
Year        : 1963

Compress the PowerShell expression output:

PS C:\>@{Account="User01";Domain="Domain01";Admin="True"} | ConvertTo-Expression -Expand -1	

@{'Admin'='True';'Account'='User01';'Domain'='Domain01'}

Convert the WinInit Process to a PowerShell expression:

PS C:\>WinInitProcess = Get-Process WinInit | ConvertTo-Expression

Reveal complex object hierarchies:

PS C:\>Get-Host | ConvertTo-Expression -Depth 4

Inputs

Any. Each objects provided through the pipeline will converted to an expression. To concatinate all piped objects in a single expression, use the unary comma operator, e.g.: ,$Object | ConvertTo-Expression

Outputs

String[]. ConvertTo-Expression returns a PowerShell expression for each input object.

Parameters

-InputObject
Specifies the objects to convert to a PowerShell expression. Enter a variable that contains the objects, or type a command or expression that gets the objects. You can also pipe one or more objects to ConvertTo-Expression.

-Depth
Specifies how many levels of contained objects are included in the PowerShell representation. The default value is 9.

-Expand
Specifies till what level the contained objects are expanded over separate lines and indented according to the -Indentation and -IndentChar parameters. The default value is 9.

A negative value will remove redundant spaces and compress the PowerShell expression to a single line (except for multi-line strings).

Xml documents and multi-line strings are embedded in a “here string” and aligned to the left.

-Indentation
Specifies how many IndentChars to write for each level in the hierarchy.

-IndentChar
Specifies which character to use for indenting.

-Strong
By default, the ConvertTo-Expression cmdlet will return a weakly typed expression which is best for transfing objects between differend PowerShell systems. The -Strong parameter will strickly define value types and objects in a way that they can still be read by same PowerShell system and PowerShell system with the same configuration (installed modules etc.).

-Explore
In explore mode, all type prefixes are omitted in the output expression (objects will cast to to hash tables). In case the -Strong parameter is also supplied, all orginal (.Net) type names are shown. The -Explore switch is usefull for exploring object hyrachies and data type, not for saving and transfering objects.

-NewLine
Specifies which characters to use for a new line. The default is defined by the operating system.