powershell rename-item replace with variables incrementing

Question

I'm trying to use the output of a Get-Childitem | Where-Object to rename a group of files but instead of rename with a constant name I want to rename with a group of variables, and I'm use the operator -replace to find where in the string is what I want to change. Example:

nane_01 -> name_23
name_02 -> name_24  they are not with the same final digit

this is the code I'm using for test:

$a = 0
$b = 1
$Na= 2
$Nb= 3
Get-Childitem | Where-Object {$_.name -match "_0[1-9]"} | rename-item -Newname { $_.name  -replace "_{0}{1}","_{2}{3}" -f $a++,$b++,$Na++,$Nb++ } -Whatif

I can't find how to make incremental variable work with the -replace operator

Answer 1

1. Specify the scope of variables explicitly, otherwise a local copy would be discarded on each invocation of the rename scriptblock.

2. Search/replace string of -replace operator are separate parameters, so format them separately using parentheses around each one (otherwise PowerShell will try to apply -f to $_.name).

$script:a = 0
$script:b = 1
$script:Na= 2
$script:Nb= 3

Get-Childitem | Where-Object {$_.name -match "_0[1-9]"} | rename-item -Newname {
    $_.name -replace ("_{0}{1}" -f $script:a++,$script:b++),
                     ("_{0}{1}" -f $script:Na++,$script:Nb++)
} -Whatif

Or just use one variable:

$script:n = 0

Get-Childitem | Where-Object {$_.name -match "_0[1-9]"} | rename-item -Newname {
    $_.name -replace ("_{0}{1}" -f $script:n++,$script:n++),
                     ("_{0}{1}" -f $script:n++,$script:n++)
} -Whatif