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I'm attempting to remove the defining of variables from a script and read them in from an XML configuration file similar to the below:

XML File

<?xml version="1.0" encoding="utf-8" ?> <settings> <process>FALSE</process> <xmlDir>\\serv1\dev</xmlDir> <scanDir>\\serv1\dev</scanDir> <processedDir>\\serv1\dev\done</processedDir> <errorDir>\\serv1\dev\err</errorDir> <log>\\serv1\dev\log\dev-Log##DATE##.log</log> <retryDelay>5</retryDelay> <retryLimit>3</retryLimit> </settings>

Then parse the XML in the script with the below:

[xml]$configFile = Get-Content $PSScriptRoot\$confFile $settings = $configFile.settings.ChildNodes foreach ($setting in $settings) { New-Variable -Name $setting.LocalName -Value ($setting.InnerText -replace '##DATE##',(get-date -f yyyy-MM-dd)) -Force }

This works great but the problem is that they are all read as a string but some I require as an integer. To get around this issue I'm having to change them to integer after the variables have been created as below:

$retryDelay = ([int]$retryDelay) $retryLimit = ([int]$retryLimit)

Although this works, I'd like to have other variables in the XML such as boolean $true / $false (and read in as a boolean) and would rather have the foreach be able to handle their types rather than additional lines in the script. Any clues appreciated.

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    XML has no type information unless you add it. Knowing nothing else, every element and attribute value is a string. Maybe you want to use JSON as your config file format? Commented Oct 25, 2017 at 12:54

2 Answers 2

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Firstly, never read XML files like this. This breaks the encoding detection that is built into XML parsers and will result in mangling your data sooner or later.

# BAD, DO NOT USE [xml]$configFile = Get-Content $PSScriptRoot\$confFile

Reading XML files properly works like this - create a new XML object and let it handle the file loading:

$configFile = New-Object xml $configFile.Load("$PSScriptRoot\$confFile")

Secondly, I strongly advise against creating global variables from a file. This is bad style as it can easily break your program by blindly overriding existing variables. Use a hash to store the values from the file, or simply use the XML file directly as your config.

$config = @{} foreach ($setting in $configFile.SelectNodes("/settings/*") ) { $config[$setting.Name] = $setting.InnerText }

Thirdly, XML has no inherent data type information. Everything is a string until you add more info about it. One way could be a type attribute (type="string" can be seen as default):

<settings> <process type="boolean">FALSE</process> <xmlDir type="string">\\serv1\dev</xmlDir> <scanDir type="string">\\serv1\dev</scanDir> <processedDir type="string">\\serv1\dev\done</processedDir> <errorDir type="string">\\serv1\dev\err</errorDir> <log type="string">\\serv1\dev\log\dev-Log##DATE##.log</log> <retryDelay type="int">5</retryDelay> <retryLimit type="int">3</retryLimit> </settings>

Of course the type attribute means nothing in and of itself. You need to write the code that pays attention to these attributes and does the necessary type conversions (if ($setting.type -eq "boolean") { ... } etc).

Fourthly, I believe you will be much better-off with simply using JSON as your config file format. It's easier to edit and it has inherent data type information.

{ "settings": { "process": false, "xmlDir": "\\\\serv1\\dev", "scanDir": "\\\\serv1\\dev", "processedDir": "\\\\serv1\\dev\\done", "errorDir": "\\\\serv1\\dev\\err", "log": "\\\\serv1\dev\\log\\dev-Log##DATE##.log", "retryDelay": 5, "retryLimit": 3 } }

Use the ConvertFrom-JSON cmdlet to parse the data. Use Get-Content -Encoding UTF8 to read it.

Using the Encoding parameter is important when dealing with text files, also when you write a file with Set-Content or Out-File. There is no hidden magic that does the right thing here, you must be explicit about the encoding.

Here is some more in-depth information about the behavior of Out-File and Set-Content. Powershell set-content and out-file what is the difference?

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5 Comments

Thanks for the info @Tomalak, much appreciated! I think it's probably easier to use JSON as you suggest. I presume I can iterate through the JSON using foreach, similar to how I parse the XML?
Well. If you structure the JSON like shown, iteration would have to be based on $config.settings | Get-Member -Type NoteProperty | .... Also see this earlier answer of mine for some more explanation on this.
BUT, as I said, I am not a fan of the whole idea of using a loop to fill variables from a config file. Your config file contains your settings. Your program knows what settings to expect, what names they have and what default values they have. You can use the $config variable as-is in your program, there is no need to transfer its contents anyplace else. Just use $retryLimit = $config.settings.retryLimit or juse $config.settings.retryLimit directly when you need it.
Now if you want to handle the case where $config.settings.retryLimit might be unset, there is a way to do that, too. In JavaScript your would say config.settings.retryLimit || 3 to make it default to 3 in case it is undefined. Just lile in Javascript, it's not an error to access a property that is unset in Powershell. You would just get $null. The construct to set it the default to 3 in Powershell would be ($config.settings.retryLimit, 3 -ne $null)[0] and the explanation why that is so is here: stackoverflow.com/a/17647824/18771
In the hope that someone finds this - if you're trying to inspect windows packet filtering platform firewall configuration exports - generated by netsh wfp show filters - you need to use this technique and not get-content
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I agree with Tomalak's answer, JSON is probably better for your use case. Here's a practical example to show you how you might use it. This is using a Custom Object created from a hashtable from which to generate the JSON and save it to a file:

$Config = [pscustomobject]@{ Process = $false xmldir = '\\serv1\dev' scanDir = '\\serv1\dev' processedDir = '\\serv1\dev\done' errorDir = '\\serv1\dev\err' log = '\\serv1\dev\log\dev-Log##DATE##.log' retryDelay = 5 retryLimit = 3 } $Config | ConvertTo-Json | Out-File .\config.txt -Encoding UTF8

This creates JSON that looks like this:

{ "Process": false, "xmldir": "\\\\serv1\\dev", "scanDir": "\\\\serv1\\dev", "processedDir": "\\\\serv1\\dev\\done", "errorDir": "\\\\serv1\\dev\\err", "log": "\\\\serv1\\dev\\log\\dev-Log##DATE##.log", "retryDelay": 5, "retryLimit": 3 }

And can be read like this:

$Settings = Get-Content .\config.txt -Encoding UTF8 | ConvertFrom-Json

Because of the way you can see that JSON is storing the variables, PowerShell does a better job of correctly typing them when they are read back in.

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Get-Content does not neither default to UTF-8 not has it any file encoding detection magic, but that's the underlying assumption for many people. Always use an explicit Encoding setting when reading/writing text files.
See here: stackoverflow.com/questions/10655788/… for details on how Out-File and Set-Content behave and handle file encoding.
@Mark Wragg thanks very much. Really appreciated the assistance.

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