Bulk rename files in powershell and add a count to each filename

I am able to bulk rename files in a directory OR substitute each file name with a count, however I need both combined.

Bulk rename (keep first 2 charachters of original name):

Get-ChildItem * |  
    Rename-Item -NewName { $_.BaseName.Split('-')[0] + $_.Extension }

(partially hard coded solution, I know!)

Alternatively, add count:

$count = 1
Get-ChildItem * | % { Rename-Item $_ -NewName (‘{0}.xlsx’ -f $count++) }

(I am not even dreaming about trailing 0s)

I tried to combine both things, but to no avail. What am I doing wrong?

My failed attempt:

$count = 1 
Get-ChildItem * |
    Rename-Item -NewName { $_.BaseName.Split('-')[0] -f $count++ + $_.Extension }

Solution

You're misunderstanding how the format operator works. You need a format string with a placeholder ({0}) in order to make that operator work. I would also recommend putting grouping parentheses around that expression, even though that shouldn't be required in this case. Just to be on the safe side.

('foo {0} bar' -f $some_var) + $other_var

With that said, you apparently want to append the value of the counter variable to the fragment from the original file name rather than using that fragment as a format string. For that you can simply concatenate the counter to the fragment, just like you do with the extension.

For the counter to work correctly you also need to specify the correct scope. The way you're using it defines a new variable $counter in the local scope of the scriptblock every time a file is renamed, so the variable $counter in the parent scope is never incremented. Use the script: or global: scope modifier to get the variable you actually intend to use.

$count = 1
Get-ChildItem * |
    Rename-Item -NewName { $_.BaseName.Split('-')[0] + $script:count++ + $_.Extension }

If you do want to use the format operator instead of string concatenation (+) you'd use it like this:

$count = 1
Get-ChildItem * |
    Rename-Item -NewName { '{0}{1}{2}' -f $_.BaseName.Split('-')[0], $script:count++, $_.Extension }