Performing A String Operation in a -replace Expression - powershell

Question

I'm trying to make using of String.Substring() to replace every string with its substring from a certain position. I'm having a hard time figuring out the right syntax for this.
$dirs = Get-ChildItem -Recurse $path | Format-Table -AutoSize -HideTableHeaders -Property #{n='Mode';e={$_.Mode};width=50}, #{n='LastWriteTime';e={$_.LastWriteTime};width=50}, #{n='Length';e={$_.Length};width=50}, #{n='Name';e={$_.FullName -replace "(.:.*)", "*($(str($($_.FullName)).Substring(4)))*"}} | Out-String -Width 40960
I'm referring to the following expression
e={$_.FullName -replace "(.:.*)", "*($(str($($_.FullName)).Substring(4)))*"}}
The substring from the 4th character isn't replacing the Full Name of the path.
The paths in question are longer than 4 characters.
The output is just empty for the Full Name when I run the script.
Can someone please help me out with the syntax
EDIT
The unaltered list of strings (as Get-ChildItem recurses) would be
D:\this\is\where\it\starts
D:\this\is\where\it\starts\dir1\file1
D:\this\is\where\it\starts\dir1\file2
D:\this\is\where\it\starts\dir1\file3
D:\this\is\where\it\starts\dir1\dir2\file1
The $_.FullName will therefore take on the value of each of the strings listed above.
Given an input like D:\this\is or D:\this\is\where, then I'm computing the length of this input (including the delimiter \) and then replacing $_.FullName with a substring beginning from the nth position where n is the length of the input.
If input is D:\this\is, then length is 10.
Expected output is
\where\it\starts
\where\it\starts\dir1\file1
\where\it\starts\dir1\file2
\where\it\starts\dir1\file3
\it\starts\dir1\dir2\file1

Answer 1

If you want to remove a particular prefix from a string you can do so like this:
$prefix = 'D:\this\is'
...
$_.FullName -replace ('^' + [regex]::Escape($prefix))
To remove a prefix of a given length you can do something like this:
$len = 4
...
$_.FullName -replace "^.{$len}"

Answer 2

When having trouble, simplify:
This function will do what you are apparently trying to accomplish:
Function Remove-Parent {
param(
[string]$Path,
[string]$Parent)
$len = $Parent.length
$Path.SubString($Len)
}
The following is not the way you likely would use it but does demonstrate that the function returns the expected results:
#'
D:\this\is\where\it\starts
D:\this\is\where\it\starts\dir1\file1
D:\this\is\where\it\starts\dir1\file2
D:\this\is\where\it\starts\dir1\file3
D:\this\is\where\it\starts\dir1\dir2\file1
'# -split "`n" | ForEach-Object { Remove-Parent $_ 'D:\This\Is' }
# Outputs
\where\it\starts
\where\it\starts\dir1\file1
\where\it\starts\dir1\file2
\where\it\starts\dir1\file3
\where\it\starts\dir1\dir2\file1
Just call the function with the current path ($_.fullname) and the "prefix" you are expecting to remove.
The function above is doing this strictly on 'length' but you could easily adapt it to match the actual string with either a string replace or a regex replace.
Function Remove-Parent {
param(
[string]$Path,
[string]$Parent
)
$remove = [regex]::Escape($Parent)
$Path -replace "^$remove"
}
The output was the same as above.