Recently, I came across an interesting bug in PowerShell. Let\u2019s create a repro.<\/p>\n
First, we create a string \u201ca\u201d and generate an xml based representation of it using the Export-Clixml cmdlet. Since we need to have the class id, we pipe the string to format-table as shown in the example below.<\/p>\n
PS><\/span> "a"<\/span> |<\/span> format-table<\/span> -auto<\/span> |<\/span> Export-Clixml<\/span> a.xml<\/span><\/pre>\n<\/font><\/p>\n
Here is the content of the xml file.<\/p>\n
<Objs Version="1.1.0.1" xmlns="http:\/\/schemas.microsoft.com\/powershell\/2004\/04">
<Obj RefId="0">
<TN RefId="0">
<T>Microsoft.PowerShell.Commands.Internal.Format.FormatEntryData<\/T>
<T>Microsoft.PowerShell.Commands.Internal.Format.PacketInfoData<\/T>
<T>Microsoft.PowerShell.Commands.Internal.Format.FormatInfoData<\/T>
<T>System.Object<\/T>
<\/TN>
<ToString>Microsoft.PowerShell.Commands.Internal.Format.FormatEntryData<\/ToString>
<Props>
<S N="ClassId2e4f51ef21dd47e99d3c952918aff9cd">27c87ef9bbda4f709f6b4002fa4af63c<\/font><\/S>
<Obj N="formatEntryInfo" RefId="1">
<TN RefId="1">
<T>Microsoft.PowerShell.Commands.Internal.Format.RawTextFormatEntry<\/T>
<T>Microsoft.PowerShell.Commands.Internal.Format.FormatEntryInfo<\/T>
<T>Microsoft.PowerShell.Commands.Internal.Format.FormatInfoData<\/T>
<T>System.Object<\/T>
<\/TN>
<ToString>Microsoft.PowerShell.Commands.Internal.Format.RawTextFormatEntry<\/ToString>
<Props>
<S N="ClassId2e4f51ef21dd47e99d3c952918aff9cd">29ED81BA914544d4BC430F027EE053E9<\/S>
<S N="text">a<\/S>
<\/Props>
<\/Obj>
<B N="outOfBand">true<\/B>
<B N="writeErrorStream">false<\/B>
<\/Props>
<\/Obj>
<\/Objs><\/font><\/pre>\nThen, we remove the class id (in blue) and save the xml file. Next, we recreate an object using the import-cliXml cmdlet and we assign it to a variable, i.e. $a. We should get an exception because the class id is missing but, we do not.<\/p>\n
PS><\/span> $a<\/span> =<\/span> Import-Clixml<\/span> .\\a.xml<\/span><\/font><\/pre>\nOn the other hand, if we execute the same command without assigning it to a variable, the exception is thrown.<\/p>\n
PS><\/span> Import-Clixml<\/span> .\\a.xml<\/span>
<\/pre>\nUnknown class Id . \n
+ CategoryInfo : InvalidData: (Microsoft.Power…FormatEntryData:PS <\/p>\nObject) [out-lineoutput], PSArgumentException <\/p>\n
+ FullyQualifiedErrorId : FormatObjectDeserializerDeserializeInvalidClassId, <\/p>\n
Microsoft.PowerShell.Commands.OutLineOutputCommand<\/font><\/p>\n
Why is this happening?<\/h3>\n
In the first instance, the object gets assigned to the variable and it never goes to the F&O system. Thus the terminating error is never generated. <\/p>\n
The workaround<\/h3>\n
The fix is fairly simple, Out-String will send the object to the host through the F&O system. <\/p>\n
PS><\/span> $a<\/span> =<\/span> Import-Clixml<\/span> .\\a.xml<\/span> |<\/span> Out-String<\/span><\/pre>\nout-lineoutput : Unknown class Id . \n
+ CategoryInfo : InvalidData: (Microsoft.Power…FormatEntryData:PSObject <\/p>\n ) [out-lineoutput], PSArgumentException <\/p>\n
+ FullyQualifiedErrorId : FormatObjectDeserializerDeserializeInvalidClassId,Micros <\/p>\n
oft.PowerShell.Commands.OutLineOutputCommand<\/font><\/p>\n
To make sure our script ends nicely, we catch the terminating error. <\/p>\n
$e<\/span> =<\/span> $null<\/span>\ntry<\/span>{<\/span> \n Import-Clixml<\/span> .\\a.xml<\/span> |<\/span> Out-String<\/span> \n}<\/span> \ncatch<\/span>{<\/span> \n $e<\/span> =<\/span> $_<\/span> \n}<\/span> \nIf<\/span>(<\/span>$e<\/span> \u2013ne<\/span> $null<\/span>)<\/span> {<\/span> $e<\/span>.<\/span>FullyQualifiedErrorId<\/span> }<\/span><\/pre>\nFormatObjectDeserializerDeserializeInvalidClassId,Microsoft.PowerShell.Commands.OutLineOut \n
putCommand<\/font><\/p>\nCheers, \n
Francisco Gomez Gamino [MSFT]<\/p>\n","protected":false},"excerpt":{"rendered":"
Recently, I came across an interesting bug in PowerShell. Let\u2019s create a repro. First, we create a string \u201ca\u201d and generate an xml based representation of it using the Export-Clixml cmdlet. Since we need to have the class id, we pipe the string to format-table as shown in the example below. PS> "a" | format-table […]<\/p>\n","protected":false},"author":600,"featured_media":13641,"comment_status":"open","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":{"_acf_changed":false,"footnotes":""},"categories":[1],"tags":[],"class_list":["post-3121","post","type-post","status-publish","format-standard","has-post-thumbnail","hentry","category-powershell"],"acf":[],"blog_post_summary":"
Recently, I came across an interesting bug in PowerShell. Let\u2019s create a repro. First, we create a string \u201ca\u201d and generate an xml based representation of it using the Export-Clixml cmdlet. Since we need to have the class id, we pipe the string to format-table as shown in the example below. PS> "a" | format-table […]<\/p>\n","_links":{"self":[{"href":"https:\/\/devblogs.microsoft.com\/powershell\/wp-json\/wp\/v2\/posts\/3121","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/devblogs.microsoft.com\/powershell\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/devblogs.microsoft.com\/powershell\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/devblogs.microsoft.com\/powershell\/wp-json\/wp\/v2\/users\/600"}],"replies":[{"embeddable":true,"href":"https:\/\/devblogs.microsoft.com\/powershell\/wp-json\/wp\/v2\/comments?post=3121"}],"version-history":[{"count":0,"href":"https:\/\/devblogs.microsoft.com\/powershell\/wp-json\/wp\/v2\/posts\/3121\/revisions"}],"wp:featuredmedia":[{"embeddable":true,"href":"https:\/\/devblogs.microsoft.com\/powershell\/wp-json\/wp\/v2\/media\/13641"}],"wp:attachment":[{"href":"https:\/\/devblogs.microsoft.com\/powershell\/wp-json\/wp\/v2\/media?parent=3121"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/devblogs.microsoft.com\/powershell\/wp-json\/wp\/v2\/categories?post=3121"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/devblogs.microsoft.com\/powershell\/wp-json\/wp\/v2\/tags?post=3121"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}