Leftpad doesn't work when using with regex in Powershell

Here are two code blocks which show the strange behavior that Leftpad does.

$array = "z", "fg"
$array -replace "(\w{1,2})", '$1'.PadLeft(2, "0")
# output: z, fg

$array = "z", "fg"
$array -replace "(\w{1,2})", '$1'.PadLeft(3, "0")
# output: 0z, 0fg

How comes the pad length not fixed?

EDIT: @LotPings

I ask this another question is because of your way of doing it when applied to rename-item statement will not affect files with brackets in its names.

$file_names = ls "G:\Donwloads\Srt Downloads\15" -Filter *.txt
# the files are: "Data Types _ C# _ Tutorial 5.txt", "If Statements (con't) _ C# _ Tutorial 15.txt"
$file_names | 
    ForEach{
        if ($_.basename -match '^([^_]+)_[^\d]+(\d{1,2})$')
            { 
            $file_names | 
                Rename-Item -NewName `
                    { ($_.BaseName -replace $matches[0], ("{0:D2}. {1}" -f [int]$matches[2],$matches[1])) + $_.Extension }
            } 
           }

# output: 05. Data Types.txt
#         If Statements (con't) _ C# _ Tutorial 15.txt

As for the .PadLeft, I thought that the regex replacement group is of string type, it should work with .PadLeft but it doesn't.

Ansgars comment to your last question should have shown that your assumption on the order of actions was wrong.
And Lee_Dailey proved you wrong another time.

My answer to your previous question presented an alternative which also works here:

("Data Types _ C# _ Tutorial 5", "If Statements (con't) _ C# _ Tutorial 15") |
  ForEach{ 
    if ($_ -match '^([^_]+)_[^\d]+(\d{1,2})$'){
      "{0:D2}. {1}" -f [int]$matches[2],$matches[1]
    } 
  }

Sample output:

05. Data Types
15. If Statements (con't)

---

The last edit to your question is in fact a new question...

• Rename-Item accepts piped input, so no ForEach-Object neccessary when also using
• Where-Object with the -match operator to replace the if.
  the $Matches collection is supplied the same way.
• I really don't know why you insist on using the -replace operator when building the NewName from scratch with the -format operator.

---

$file_names = Get-ChildItem "G:\Donwloads\Srt Downloads\15" -Filter *.txt

$file_names | Where-Object BaseName -match '^([^_]+)_[^\d]+(\d{1,2})$' |
    Rename-Item -NewName {"{0:D2}. {1}{2}" -f [int]$matches[2],$matches[1].Trim(),$_.Extension} -WhatIf