Powershell rename-item, replace old name using functions

Question

I have a list of files:

PS S:\temp> dir


    Directory: S:\temp


Mode                LastWriteTime     Length Name
----                -------------     ------ ----
-a---         3/28/2016   2:07 AM          0 00001_asdfasdfsa df.txt
-a---         3/28/2016   2:07 AM          0 00002_asdfasdfsa df - Copy (3).txt
-a---         3/28/2016   2:07 AM          0 00003_asdfasdfsa df - Copy.txt
-a---         3/28/2016   2:07 AM          0 00004_asdfasdfsa df - Copy (6).txt
-a---         3/28/2016   2:07 AM          0 00005_asdfasdfsa df - Copy (5).txt
-a---         3/28/2016   2:07 AM          0 00006_asdfasdfsa df - Copy (4).txt
-a---         3/28/2016   2:07 AM          0 00007_asdfasdfsa df - Copy (2).txt
-a---         3/28/2016   2:07 AM          0 700006_asdfasdfsa df - Copy (4) - Copy.txt


PS S:\temp>

I want to renamem those that start with five numbers and an underline. The new name will add a number I specified to the leading numbers of those file names. For example, if I add 10, the new names would be:

PS S:\temp> dir


    Directory: S:\temp


Mode                LastWriteTime     Length Name
----                -------------     ------ ----
-a---         3/28/2016   2:07 AM          0 00011_asdfasdfsa df.txt
-a---         3/28/2016   2:07 AM          0 00012_asdfasdfsa df - Copy (3).txt
-a---         3/28/2016   2:07 AM          0 00013_asdfasdfsa df - Copy.txt
-a---         3/28/2016   2:07 AM          0 00014_asdfasdfsa df - Copy (6).txt
-a---         3/28/2016   2:07 AM          0 00015_asdfasdfsa df - Copy (5).txt
-a---         3/28/2016   2:07 AM          0 00016_asdfasdfsa df - Copy (4).txt
-a---         3/28/2016   2:07 AM          0 00017_asdfasdfsa df - Copy (2).txt
-a---         3/28/2016   2:07 AM          0 700006_asdfasdfsa df - Copy (4) - Copy.txt


PS S:\temp>

Now my PowerShell code is:

dir * | ?{$_.name -match '^\d{5}_.+'} | Rename-Item -NewName {$_.name -replace '^(\d{5})(_.+)', ((([convert]::ToInt32('$1', 10) + 12).ToString("00000")) + '$2')} -whatif

I can't find any errors in my code. But when I run it, I got the following error message:

Rename-Item : The input to the script block for parameter 'NewName' failed. Exception calling "ToInt32" with "2" argument(s): "Could not find any recognizable digits."
At line:1 char:62
+ dir * | ?{$_.name -match '^\d{5}_.+'} | Rename-Item -NewName {$_.name -replace ' ...
+ ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
    + CategoryInfo          : InvalidArgument: (S:\temp\00001_asdfasdfsa df.txt:PSObject) [Rename-Item], ParameterBindingException
    + FullyQualifiedErrorId : ScriptBlockArgumentInvocationFailed,Microsoft.PowerShell.Commands.RenameItemCommand

My question is, where I am wrong? Is it because I should not use functions in the replacement part of the replace operator? If so, how to write complex logic in -newname{}? Thanks.

The reason your replace did not work is because of how -replace works. See this answer: http://stackoverflow.com/questions/8163061/passing-a-function-to-powershells-replace-function. Basically '$1' literally means the string "$1" and the regex engine does not get its hands on it. — Matt, Mar 27 '16 at 22:56

score 1 · Accepted Answer · edited May 23 '17 at 11:50

You cannot use -replace and massage the data at the time of the substitution. Your replacement was failing as the string literal $1 cannot be converted to integer. As discussed in a similar question: Passing a function to Powershell's (replace) function you can use a scriptblock and the .nNet regex static method Replace.

$replaceBlock = {
    # Groups 0 contains the whole match. 1 is the first group... and so on.
    ([convert]::ToInt32($args[0].Groups[1],10) + 12).ToString("00000") + $args[0].Groups[2]
}

Get-ChildItem | Where-Object{$_.name -match '^\d{5}_.+'} | Rename-Item -NewName {
    [Regex]::Replace($_.name, '^(\d{5})(_.+)', $replaceBlock)
} -whatif

You can use the script block inline but getting it out makes for a little cleaner code. However I would likely use -match and the returned $matches object to do the same thing.

Get-ChildItem | Where-Object{$_.name -match '^(\d{5})(_.+)'} | Rename-Item -NewName {
    ([int]$Matches[1] + 12).ToString("00000") + $Matches[2]
} -whatif

Note that I updated the where-object to have capture groups.

score 0 · Answer 2 · answered Mar 27 '16 at 18:45

Haha, I got an answer.

dir * | ?{$_.name -match '^\d{5}_.+'} | Rename-Item -NewName {(([convert]::toint32($_.name.substring(0, 5), 10) + 12).ToString("00000")) + $_.name.substring(5)} -whatif

Just found that I can use any code in the -newname{} block. But I still don't understand why my -replace way did not work.

Powershell rename-item, replace old name using functions

2 Answers2