PowerShell: How to find a word within a line of text and modify the data behind it - string

Question

I'm looking for a way to find a word with a value behind it in a piece of text and then update the value.
Example:
In the file the are multiple occurrences of 'schema="anon" maxFileSize="??????" maxBufferSize="123"'
I want to find all the lines containing maxFileSize and then update the unknown value ?????? to 123456.
So far, I came up with this:
cls
$Files = "C:\temp1\file.config","C:\temp2\file.config"
$newMaxFileSize = "123456"
ForEach ($File in $Files) {
If ((Test-Path $File -PathType Leaf) -eq $False) {
Write-Host "File $File doesn't exist"
} Else {
# Check content of file and select all lines where maxFileSize isn't equal to 123456 yet
$Result = Get-Content $File | Select-String -Pattern "maxFileSize" -AllMatches | Select-String -Pattern "123456" -NotMatch -AllMatches
Write-Host $Result
<#
ROUTINE TO UPDATE THE SIZE
#>
}
}
Yet, I have no clue how to find the word "maxFileSize", let alone how to update the value behind it...

Answer 1

Assuming the input file is actually XML, use the following XPath expression to locate all nodes that have a maxFileSize attribute (regardless of value):
# Parse input file as XML
$configXml = [xml](Get-Content $file)
# Use Select-Xml to find relevant nodes
$configXml |Select-Xml '//*[#maxFileSize]' |ForEach-Object {
# Update maxFileSize attribute value
$_.Node.SetAttribute('maxFileSize','123456')
}
# Overwrite original file with updated XML
$configXml.Save($file.FullName)
If the config file is some archaic format for which no readily available parser exists, use the -replace operator to update the value where appropriate:
$Results = #(Get-Content $File) -creplace '(?<=maxFileSize=")[^"]*(?=")','123456'
The pattern used above, (?<=maxFileSize=")[^"]*(?="), describes:
(?<= # Positive look-behind assertion, this pattern MUST precede the match
maxFileSize=" # literal string `maxFileSize="`
) # Close look-behind
[^"]* # Match 0 or more non-" characters
(?= # Positive look-ahead assertion, this pattern MUST succeed the match
" # literal string `"`
) # Close look-ahead