问题
How can I accomplish something like this:
PS /home/nicholas/powershell>
PS /home/nicholas/powershell> $date=(Get-Date | ConvertTo-Xml)
PS /home/nicholas/powershell>
PS /home/nicholas/powershell> $date
xml Objects
--- -------
version="1.0" encoding="utf-8" Objects
PS /home/nicholas/powershell>
PS /home/nicholas/powershell> $date.OuterXml
<?xml version="1.0" encoding="utf-8"?><Objects><Object Type="System.DateTime">12/12/2020 2:43:46 AM</Object></Objects>
PS /home/nicholas/powershell>
but, instead, reading in a file?
how do I load/import/read/convert an xml file using ConvertTo-Xml for parsing with Select-Xml using Xpath?
PS /home/nicholas/powershell>
PS /home/nicholas/powershell> $xml=ConvertTo-Xml ./bookstore.xml
PS /home/nicholas/powershell>
PS /home/nicholas/powershell> $xml
xml Objects
--- -------
version="1.0" encoding="utf-8" Objects
PS /home/nicholas/powershell>
PS /home/nicholas/powershell> $xml.InnerXml
<?xml version="1.0" encoding="utf-8"?><Objects><Object Type="System.String">./bookstore.xml</Object></Objects>
PS /home/nicholas/powershell>
PS /home/nicholas/powershell> $xml.OuterXml
<?xml version="1.0" encoding="utf-8"?><Objects><Object Type="System.String">./bookstore.xml</Object></Objects>
PS /home/nicholas/powershell>
PS /home/nicholas/powershell> cat ./bookstore.xml
<?xml version="1.0"?>
<!-- A fragment of a book store inventory database -->
<bookstore xmlns:bk="urn:samples">
<book genre="novel" publicationdate="1997" bk:ISBN="1-861001-57-8">
<title>Pride And Prejudice</title>
<author>
<first-name>Jane</first-name>
<last-name>Austen</last-name>
</author>
<price>24.95</price>
</book>
<book genre="novel" publicationdate="1992" bk:ISBN="1-861002-30-1">
<title>The Handmaid's Tale</title>
<author>
<first-name>Margaret</first-name>
<last-name>Atwood</last-name>
</author>
<price>29.95</price>
</book>
<book genre="novel" publicationdate="1991" bk:ISBN="1-861001-57-6">
<title>Emma</title>
<author>
<first-name>Jane</first-name>
<last-name>Austen</last-name>
</author>
<price>19.95</price>
</book>
<book genre="novel" publicationdate="1982" bk:ISBN="1-861001-45-3">
<title>Sense and Sensibility</title>
<author>
<first-name>Jane</first-name>
<last-name>Austen</last-name>
</author>
<price>19.95</price>
</book>
</bookstore>
PS /home/nicholas/powershell>
Creating the xml file within the REPL console itself works as expected:
How to parse XML in Powershell with Select-Xml and Xpath?
回答1:
Properly reading an XML document in Powershell works like this:
$doc = New-Object xml
$doc.Load( (Convert-Path bookstore.xml) )
XML can come in numerous file encodings, and using the XmlDocument.Load method makes sure the file is read properly without prior knowledge of the encoding.
Not reading a file with the correct encoding will result in mangled data or errors except in very basic or very lucky cases.
The often-seen method of using Get-Content and casting the resulting string to [xml] is the wrong way of dealing with XML for this very reason. So don't do that.
You can get a correct result with Get-Content, but that requires
- prior knowledge of the file encoding (e.g.
Get-Content bookstore.xml -Encoding UTF-8) - hard-coding the file encoding into your script (meaning it will break if the XML encoding ever changes unexpectedly)
- limiting yourself to the very few file encodings that
Get-Contentsupports (XML supports more)
It means you put yourself in a position where you have to manually think about and solve a problem that XML has been specifically designed to automatically handle for you.
Doing things correctly with Get-Content is a lot of unnecessary extra work and limitations. And doing things incorrectly is pointless when doing it right is so easy.
Examples, after loading $doc like shown above.
$doc.bookstore.book
prints a list of <book> elements and their properties
genre : novel
publicationdate : 1997
ISBN : 1-861001-57-8
title : Pride And Prejudice
author : author
price : 24.95
genre : novel
publicationdate : 1992
ISBN : 1-861002-30-1
title : The Handmaid's Tale
author : author
price : 29.95
genre : novel
publicationdate : 1991
ISBN : 1-861001-57-6
title : Emma
author : author
price : 19.95
genre : novel
publicationdate : 1982
ISBN : 1-861001-45-3
title : Sense and Sensibility
author : author
price : 19.95
$doc.bookstore.book | Format-Table
prints the same thing as a table
genre publicationdate ISBN title author price
----- --------------- ---- ----- ------ -----
novel 1997 1-861001-57-8 Pride And Prejudice author 24.95
novel 1992 1-861002-30-1 The Handmaid's Tale author 29.95
novel 1991 1-861001-57-6 Emma author 19.95
novel 1982 1-861001-45-3 Sense and Sensibility author 19.95
$doc.bookstore.book | Where-Object publicationdate -lt 1992 | Format-Table
filters the data
genre publicationdate ISBN title author price
----- --------------- ---- ----- ------ -----
novel 1991 1-861001-57-6 Emma author 19.95
novel 1982 1-861001-45-3 Sense and Sensibility author 19.95
$doc.bookstore.book | Where-Object publicationdate -lt 1992 | Sort publicationdate | select title
sorts and prints only the <title> field
title
-----
Sense and Sensibility
Emma
There are many more ways of slicing and dicing the data, it all depends on what you want to do.
来源：https://stackoverflow.com/questions/65263942/how-to-load-or-read-an-xml-file-using-convertto-xml-and-select-xml