Need to batch add characters to filenames using Powershell - powershell

Question

I have a series of files all named something like:
PRT14_WD_14220000_1.jpg
I need to add two zeroes after the last underscore and before the number so it looks like PRT14_WD_14220000_001.jpg
I've tried"
(dir) | rename-Item -new { $_.name -replace '*_*_*_','*_*_*_00' }
Appreciate any help.

Answer 1

The closest thing to what you attempted would be this. In regex, the wildcard is .*. And the parentheses do grouping to refer to later with the dollar sign numbers.
dir *.jpg | rename-Item -new { $_.name -replace '(.*)_(.*)_(.*)_','$1_$2_$3_00' } -whatif
What if: Performing the operation "Rename File" on target "Item: C:\users\admin\foo\PRT14_WD_14220000_1.jpg Destination: C:\users\admin\foo\PRT14_WD_14220000_001.jpg".
Ok, here's my take when you want the number with max two zeroes padding. $num has to be an integer for the .tostring() method I want.
dir *.jpg | rename-item -newname { $a,$b,$c,$num = $_.basename -split '_'
$num = [int]$num
$a + '_' + $b + "_" + $c + '_' + $num.tostring('000') + '.jpg'
} -whatif

Answer 2

the following presumes your last part of the .BaseName will always need two zeros added to it. what it does ...
fakes getting the fileinfo object that you get from Get-Item/Get-ChildItem
replace that with the appropriate cmdlet. [grin]
splits the .BaseName into parts using the _ as the split target
adds two zeros to the final part from the above split
merges the parts into a $NewBaseName
gets the .FullName and replaces the original BaseName with the $newBaseName
displays that new file name
you will still need to do your rename, but that is pretty direct. [grin]
here's the code ...
# fake getting a file info object
# in real life, use Get-Item or Get-ChildItem
$FileInfo = [System.IO.FileInfo]'PRT14_WD_14220000_1.jpg'
$BNParts = $FileInfo.BaseName.Split('_')
$BNParts[-1] = '00{0}' -f $BNParts[-1]
$NewBasename = $BNParts -join '_'
$NewFileName = $FileInfo.FullName.Replace($FileInfo.BaseName, $NewBaseName)
$NewFileName
output = D:\Data\Scripts\PRT14_WD_14220000_001.jpg

Answer 3

The -replace operator operates on regexes (regular expressions), not wildcard expressons such as * (by itself), which is what you're trying to use.
A conceptually more direct approach is to focus the replacement on the end of the string:
Get-ChildItem | # `dir` is a built-in alias for Get-ChildItem`
Rename-Item -NewName { $_.Name -replace '(?<=_)[^_]+(?=\.)', '00$&' } -WhatIf
Note: The -WhatIf common parameter in the command above previews the operation. Remove -WhatIf once you're sure the operation will do what you want.
(?<=_)[^_]+(?=\.) matches a nonempty run (+) of non-_ chars. ([^_]) preceded by _ ((?<=_) and followed by a literal . ((?=\.)), excluding both the preceding _ and the following . from what is captured by the match ((?<=...) and (?=...) are non-capturing look-around assertions).
In short: This matches and captures the characters after the last _ and before the start of the filename extension.
00$& replaces what was matched with 00, followed by what the match captured ($&).
In a follow-up comment you mention wanting to not just blindly insert 00, but to 0-left-pad the number after the last _ to 3 digits, whatever the number may be.
In PowerShell [Core] 6.1+, this can be achieved as follows:
Get-ChildItem |
Rename-Item -NewName {
$_.Name -replace '(?<=_)[^_]+(?=\.)', { $_.Value.PadLeft(3, '0') }
} -WhatIf
The script block ({ ... }) as the replacement operand receives each match as a Match instance stored in automatic variable $_, whose .Value property contains the captured text.
Calling .PadLeft(3, '0') on that captured text 0-left-pads it to 3 digits and outputs the result, which replaces the regex match at hand.
A quick demonstration:
PS> 'PRT14_WD_14220000_1.jpg' -replace '(?<=_)[^_]+(?=\.)', { $_.Value.PadLeft(3, '0') }
PRT14_WD_14220000_001.jpg # Note how '_1.jpg' was replaced with '_001.jpg'
In earlier PowerShell versions, you must make direct use of the .NET [regex] type's .Replace() method, which fundamentally works the same:
Get-ChildItem |
Rename-Item -NewName {
[regex]::Replace($_.Name, '(?<=_)[^_]+(?=\.)', { param($m) $m.Value.PadLeft(3, '0') })
} -WhatIf