Powershell overwriting file contents with match instead of editing single line - powershell

Question

I have a text file that contains a string I want to modify.
Example text file contents:
abc=1
def=2
ghi=3
If I run this code:
$file = "c:\test.txt"
$MinX = 100
$MinY = 100
$a = (Get-Content $file) | %{
if($_ -match "def=(\d*)"){
if($Matches[1] -gt $MinX){$_ -replace "$($Matches[1])","$($MinX)" }
}
}
$a
The result is:
def=100
If I omit the greater-than check like so:
$a = (Get-Content $file) | %{
if($_ -match "def=(\d*)"){
$_ -replace "$($Matches[1])","$($MinX)"
}
}
$a
The result is correct:
abc=1
def=100
ghi=3
I don't understand how a simple integer comparison before doing the replace could screw things up so badly, can anyone advise what I'm missing?

Answer 1

The comparison operator -gt will never get you a value of $true because you need to
cast the $matches[1] string value to int first so it compares two integer numbers
2 is never greater than 100.. Change the operator to -lt instead.
Your code outputs only one line, because you forgot to also output unchanged lines that do not match the regex
$file = 'c:\test.txt'
$MinX = 100
$MinY = 100
$a = (Get-Content $file) | ForEach-Object {
if ($_ -match '^def=(\d+)'){
if([int]$matches[1] -lt $MinX){ $_ -replace $matches[1],$MinX }
}
else {
$_
}
}
$a
Or use switch (is also faster than using Get-Content):
$file = 'c:\test.txt'
$MinX = 100
$MinY = 100
$a = switch -Regex -File $file {
'^def=(\d+)' {
if([int]$matches[1] -lt $MinX){ $_ -replace $matches[1],$MinX }
}
default { $_ }
}
$a
Output:
abc=1
def=100
ghi=3

Answer 2

That's because the expression ($Matches[1] -gt $MinX) is a string comparison. In Powershell, the left-hand side of a comparison dictates the comparison type and since that is of type [string], Powershell has to cast/convert the right-hand side of the expression to [string] also. You expression, therefore, is evaluated as ([string]$Matches[1] -gt [string]$MinX).