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rchivers
rchivers

Reputation: 155

Powershell file rename syntax

I'm trying to rename all the files in a given directory so that they have the sequential format 001a.jpg, 001b.jpg, 002a.jpg etc.

I have tried:

$c=1
get-childitem * | foreach {
if($c/2=[int]($c/2)){
rename-item -NewName {($c-1) + 'b.jpg'} else rename-item - NewName {$c + 'a.jpg'}}$c++} - whatif

But I am getting "the assignment operator is not valid".

The = in the third line is obviously not supposed to be an assignment operator. I just want to check whether the counter is on an even number. I found -ne for not equal to but PS didn't seem to like the -.

I am not sure about the syntax of the new names but the parser doesn't get that far ATM.

Grateful for any pointers.

Edit: I've just realised the numbers would skip but I can fix that once I understand the problem with what I already have.

Upvotes: 3

Views: 245

Answers (2)

marsze
marsze

Reputation: 17035

Several things you need to know (some are just recommendations):

  1. Every if-else branch requires curly brackets
  2. If you do not input the items to Rename-Item via the pipeline, you have to specify the path
  3. If you specify the path for Rename-Item, you cannot use a script block for -NewName
  4. You cannot use + if the left operand is int and the right is string, because it would be interpreted as addition and requires two numbers.
  5. You cannot use the -WhatIf switch on the whole construct, but only individual commands
  6. It will suffice to use the command only once, and use the if-else only to set the new name
  7. You can simplify your condition using the modulus operator % (as explained in other answers and comments)
  8. You can use the -Begin parameter for initialization
  9. The * for Get-ChildItem is not necessary

Here is the updated code:

Get-ChildItem | foreach -Begin { $c = 1 } -Process {
    if ($c % 2) {
        $newName = "${c}a.jpg"
    }
    else {
        $newName = "$($c-1)b.jpg"
    }
    Rename-Item -LiteralPath $_.FullName -NewName $newName -WhatIf
    $c++
}

Here is an even shorter version, that pipes directly into Rename-Item

$c = 0
Get-ChildItem |
  Rename-Item -NewName {if (++$script:c % 2) {"${c}a.jpg"} else {"$($c-1)b.jpg"}} -WhatIf

Upvotes: 1

Theo
Theo

Reputation: 61028

As commented, if you do not leave spaces around the -eq or -ne operators, PowerShell will interpret the dash as belonging to the math, so

if($c/2-ne[int]($c/2))

Will fail.

Also, to test if a number is odd, it is probably quicker to do if ($c % 2) or if ($c -band 1).

Use -not to test for even numbers.

Upvotes: 3

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