{"id":2451,"date":"2015-03-10T12:22:08","date_gmt":"2015-03-10T08:22:08","guid":{"rendered":"https:\/\/rakhesh.com\/?p=2451"},"modified":"2015-03-10T15:37:52","modified_gmt":"2015-03-10T11:37:52","slug":"a-brief-intro-to-xml-powershell","status":"publish","type":"post","link":"https:\/\/rakhesh.com\/powershell\/a-brief-intro-to-xml-powershell\/","title":{"rendered":"A brief intro to XML & PowerShell"},"content":{"rendered":"

I am dealing with some XML and PowerShell for this thing I am working on. Thought it would be worth giving a brief intro to XML so the concepts are clear to myself and anyone else.<\/p>\n

From this site<\/a>, a simple XML based food menu (which I’ve slightly modified):<\/p>\n

<?xml version=\"1.0\" encoding=\"ISO8859-1\" ?>\r\n<breakfast-menu>\r\n  <food offer=\"Today's Special\">\r\n    <name>Belgian Waffles<\/name>\r\n    <price>$5.95<\/price>\r\n    <description>two of our famous Belgian Waffles with plenty of real maple syrup<\/description>\r\n    <calories>650<\/calories>\r\n  <\/food>\r\n  <food>\r\n    <name>Strawberry Belgian Waffles<\/name>\r\n    <price>$7.95<\/price>\r\n    <description>light Belgian waffles covered with strawberrys and whipped cream<\/description>\r\n    <calories>900<\/calories>\r\n  <\/food>\r\n  <food>\r\n    <name>Berry-Berry Belgian Waffles<\/name>\r\n    <price>$8.95<\/price>\r\n    <description>light Belgian waffles covered with an assortment of fresh berries and whipped cream<\/description>\r\n    <calories>900<\/calories>\r\n  <\/food>\r\n  <food>\r\n    <name>French Toast<\/name>\r\n    <price>$4.50<\/price>\r\n    <description>thick slices made from our homemade sourdough bread<\/description>\r\n    <calories>600<\/calories>\r\n  <\/food>\r\n  <food>\r\n    <name>Homestyle Breakfast<\/name>\r\n    <price>$6.95<\/price>\r\n    <description>two eggs, bacon or sausage, toast, and our ever-popular hash browns<\/description>\r\n    <calories>950<\/calories>\r\n  <\/food>\r\n<\/breakfast-menu><\/pre>\n
It’s obvious what the food menu is about. It’s a breakfast menu. It consists of food entries. Each food entry consists of the name of the food, its price, a description, and calories. One of these food items is today’s special, and is marked accordingly. Straightforward.<\/p>\n
Items such as <name><\/code> and <\/name><\/code> are called tags<\/strong>. You have an opening tag <name><\/code> <\/code> and a closing tag <\/name><\/code>. Between these tags you have an some content<\/strong> (e.g. “French Toast”). Tags can have attributes<\/strong> (e.g. offer = “Today’s Special!”). The entirety of an opening and ending tag, their attributes, and the content enclosed by these tags is called an element<\/strong>.\u00a0<\/p>\n
In the example above, the element breakfast-menu<\/code> is the the root element<\/strong>. If you visualize the listing above as a tree, you can see it all starts from breakfast-menu<\/code>. This root element has 5 children elements<\/strong>, each of which is a food<\/code> element. These children elements are also sibling elements<\/strong> to each other. Each food element in turn has 4 different<\/em> children elements (name<\/code>, price<\/code>, etc), who are themselves sibling elements to each other. \u00a0<\/p>\n
This site<\/a> has a really good intro to XML. And this site<\/a> is is a good reference on the various types such as elements, attributes, CDATA, etc.<\/p>\n
XML Notepad<\/a> is a good way to view and edit\/ create XML documents. It gives a hierarchical structure too that’s easy to understand. Here’s the above XML viewed through XML Notepad.\u00a0<\/p>\n
\"xml-notepad\"<\/a><\/p>\n
Notice how XML Notepad puts some of the elements as folders. To create a new sibling element to the food<\/code> element you would right click on the parent element breakfast-menu<\/code>\u00a0and create a new child element.\u00a0<\/p>\n
\"xml-notepad-newchild\"<\/a><\/p>\n
This will create an element that does not look like a folder. But if you right click this element and create a new child, then XML Notepad changes the icon to look like a folder.\u00a0<\/p>\n
\"xml-notepad-newchild2\"<\/a><\/p>\n
Just thought I’d point this out so it’s clear. An element containing another element has nothing special to it. In XML Notepad or when viewing the XML through a browser such as Internet Explorer, Firefox, etc they might be formatted differently, but there’s nothing special about them.\u00a0Everyone’s an element just that some have children and so appear different.\u00a0<\/p>\n
In PowerShell you can read an XML file by casting it into an [xml]<\/code> accelerator thus:<\/p>\n
[xml]$SomeVariable = Get-Content .\\path\\to\\file.xml<\/pre>\n
Using the above XML, for instance, I can then do things like this:<\/p>\n
PS> [xml]$temp = Get-Content .\\tmp.xml\r\nPS> $temp.'breakfast-menu'\r\n\r\nfood\r\n----\r\n{Belgian Waffles, Strawberry Belgian Waffles, Berry-Berry Belgian Waffles, French Toast...}\r\n\r\n\r\nPS> $temp.'breakfast-menu'.food\r\n\r\nname                                       price                                      description                               calories\r\n----                                       -----                                      -----------                               --------\r\nBelgian Waffles                            $5.95                                      two of our famous Belgian Waffles with... 650\r\nStrawberry Belgian Waffles                 $7.95                                      light Belgian waffles covered with str... 900\r\nBerry-Berry Belgian Waffles                $8.95                                      light Belgian waffles covered with an ... 900\r\nFrench Toast                               $4.50                                      thick slices made from our homemade so... 600\r\nHomestyle Breakfast                        $6.95                                      two eggs, bacon or sausage, toast, and... 950\r\n<\/pre>\n
Here’s a list of methods\u00a0available to this object:<\/p>\n
PS> $temp | Get-Member | ?{ $_.MemberType -eq \"Method\" } | Format-Wide -Column 3\r\n\r\n\r\nAppendChild                      Clone                            CloneNode\r\nCreateAttribute                  CreateCDataSection               CreateComment\r\nCreateDocumentFragment           CreateDocumentType               CreateElement\r\nCreateEntityReference            CreateNavigator                  CreateNode\r\nCreateProcessingInstruction      CreateSignificantWhitespace      CreateTextNode\r\nCreateWhitespace                 CreateXmlDeclaration             Equals\r\nGetElementById                   GetElementsByTagName             GetEnumerator\r\nGetHashCode                      GetNamespaceOfPrefix             GetPrefixOfNamespace\r\nGetType                          ImportNode                       InsertAfter\r\nInsertBefore                     Load                             LoadXml\r\nNormalize                        PrependChild                     ReadNode\r\nRemoveAll                        RemoveChild                      ReplaceChild\r\nSave                             SelectNodes                      SelectSingleNode\r\nSupports                         Validate                         WriteContentTo\r\nWriteTo<\/pre>\n
The methods vary if you are looking at a specific element:<\/p>\n
PS> $temp.'breakfast-menu'.food | Get-Member | ?{ $_.MemberType -eq \"Method\" } | Format-Wide -Column 3\r\n\r\n\r\nAppendChild                      Clone                            CloneNode\r\nCreateNavigator                  Equals                           GetAttribute\r\nGetAttributeNode                 GetElementsByTagName             GetEnumerator\r\nGetHashCode                      GetNamespaceOfPrefix             GetPrefixOfNamespace\r\nGetType                          HasAttribute                     InsertAfter\r\nInsertBefore                     Normalize                        PrependChild\r\nRemoveAll                        RemoveAllAttributes              RemoveAttribute\r\nRemoveAttributeAt                RemoveAttributeNode              RemoveChild\r\nReplaceChild                     SelectNodes                      SelectSingleNode\r\nSetAttribute                     SetAttributeNode                 Supports\r\nWriteContentTo                   WriteTo<\/pre>\n
Say I want to add a new food<\/code> element to the breakfast-menu<\/code> element. The AppendChild()<\/code> method looks interesting.\u00a0<\/p>\n
You can’t simply add a child by giving a name because it expects as input an object of type Xml.XmlNode<\/code>.\u00a0<\/p>\n
PS> $temp.'breakfast-menu'.AppendChild\r\n\r\nOverloadDefinitions\r\n-------------------\r\nSystem.Xml.XmlNode AppendChild(System.Xml.XmlNode newChild)<\/pre>\n
So you have to first create the element separately and then pass that to the AppendChild()<\/code> method. \u00a0<\/p>\n
Only the XML root object has methods to create new elements none of the elements below it have (notice the $temp<\/code> output above). So I start from there:<\/p>\n
# create variables that hold new elements called food, name, and price\r\nPS> $newFoodElem = $temp.CreateElement(\"food\")\r\nPS> $newNameElem = $temp.CreateElement(\"name\")\r\nPS> $newPriceElem = $temp.CreateElement(\"price\")\r\n\r\n# create variables holding content for name and price\r\nPS> $newNameContent = $temp.CreateTextNode(\"Italian Waffles\")\r\nPS> $newPriceContent = $temp.CreateTextNode(\"USD 16.00\") # beware of using $ as it gets treated as a variable!\r\n\r\n# update, I learnt later that it's also possible to add content to an element this way: \r\n# $newNameElem.InnerText = \"Italian Waffles\"\r\n# $newPriceElem.InnterText = \"USD 16.00\"\r\n# If I do this way I don't have to append as below either.\r\n\r\n# append the name & price content to the elements themselves\r\nPS> $newNameElem.AppendChild($newNameContent)\r\n\r\n\r\nName            : #text\r\nLocalName       : #text\r\nNodeType        : Text\r\nParentNode      : name\r\nValue           : Italian Waffles\r\nInnerText       : Italian Waffles\r\nData            : Italian Waffles\r\nLength          : 15\r\nPreviousSibling :\r\nNextSibling     :\r\nChildNodes      : {}\r\nAttributes      :\r\nOwnerDocument   : #document\r\nFirstChild      :\r\nLastChild       :\r\nHasChildNodes   : False\r\nNamespaceURI    :\r\nPrefix          :\r\nIsReadOnly      : False\r\nOuterXml        : Italian Waffles\r\nInnerXml        :\r\nSchemaInfo      : System.Xml.Schema.XmlSchemaInfo\r\nBaseURI         :\r\n\r\n\r\n\r\nPS> $newPriceElem.AppendChild($newPriceContent)\r\n\r\n\r\nName            : #text\r\nLocalName       : #text\r\nNodeType        : Text\r\nParentNode      : price\r\nValue           : USD 16.00\r\nInnerText       : USD 16.00\r\nData            : USD 16.00\r\nLength          : 3\r\nPreviousSibling :\r\nNextSibling     :\r\nChildNodes      : {}\r\nAttributes      :\r\nOwnerDocument   : #document\r\nFirstChild      :\r\nLastChild       :\r\nHasChildNodes   : False\r\nNamespaceURI    :\r\nPrefix          :\r\nIsReadOnly      : False\r\nOuterXml        : USD 16.00\r\nInnerXml        :\r\nSchemaInfo      : System.Xml.Schema.XmlSchemaInfo\r\nBaseURI         :\r\n\r\n# now append these two elements to the parent food element\r\nPS> $newFoodElem.AppendChild($newNameElem)\r\n\r\n#text\r\n-----\r\nItalian Waffles\r\n\r\n\r\nPS> $newFoodElem.AppendChild($newPriceElem)\r\n\r\n#text\r\n-----\r\nUSD 16.00\r\n\r\n\r\n# confirm\r\nPS> $newFoodElem\r\n\r\nname                                             price\r\n----                                             -----\r\nItalian Waffles                                  USD 16.00\r\n\r\n# and finally append this food element to breakfast-menu!\r\nPS> $temp.'breakfast-menu'.AppendChild($newFoodElem)\r\n\r\nname                                             price\r\n----                                             -----\r\nItalian Waffles                                  USD 16.00\r\n\r\n# confirm all is well\r\nPS> $temp.'breakfast-menu'.food\r\n\r\n\r\noffer       : Today's Special\r\nname        : Belgian Waffles\r\nprice       : $5.95\r\ndescription : two of our famous Belgian Waffles with plenty of real maple syrup\r\ncalories    : 650\r\n\r\nname        : Strawberry Belgian Waffles\r\nprice       : $7.95\r\ndescription : light Belgian waffles covered with strawberrys and whipped cream\r\ncalories    : 900\r\n\r\nname        : Berry-Berry Belgian Waffles\r\nprice       : $8.95\r\ndescription : light Belgian waffles covered with an assortment of fresh berries and whipped cream calories    : 900\r\n\r\nname        : French Toast\r\nprice       : $4.50\r\ndescription : thick slices made from our homemade sourdough bread\r\ncalories    : 600\r\n\r\nname        : Homestyle Breakfast\r\nprice       : $6.95\r\ndescription : two eggs, bacon or sausage, toast, and our ever-popular hash browns\r\ncalories    : 950\r\n\r\nname  : Italian Waffles\r\nprice : USD 16.00<\/pre>\n
Just for kicks here’s a snippet of the last two entries from the XML file itself:<\/p>\n
PS> $temp.Save(\"C:\\Users\\Rakhesh\\Desktop\\blah.xml\")\r\nPS> Get-Content .\\blah.xml<\/pre>\n
  <food>\r\n    <name>Homestyle Breakfast<\/name>\r\n    <price>$6.95<\/price>\r\n    <description>two eggs, bacon or sausage, toast, and our ever-popular hash browns<\/description >\r\n    <calories>950<\/calories>\r\n  <\/food>\r\n  <food>\r\n    <name>Italian Waffles<\/name>\r\n    <price>USD 16.00<\/price>\r\n  <\/food><\/pre>\n
Yay! That’s a crazy amount of work though just to get a new element added!\u00a0<\/p>\n
Before I forget, while writing this post I came across the following links. Good stuff:\u00a0<\/p>\n