PowerShell Script to Rename Multiple Files Easily

Use Get-ChildItem to list files and Rename-Item to rename them, for example: Get-ChildItem *.txt | Rename-Item -NewName {"new_" + $_.Name} renames all .txt files by adding 'new_' prefix.

Examples

InputFiles: report1.txt, report2.txt; Script: Get-ChildItem *.txt | Rename-Item -NewName {"new_" + $_.Name}

OutputFiles renamed to new_report1.txt, new_report2.txt

InputFiles: image1.jpg, image2.jpg; Script: Get-ChildItem *.jpg | Rename-Item -NewName { $_.BaseName + "_backup" + $_.Extension }

OutputFiles renamed to image1_backup.jpg, image2_backup.jpg

InputFiles: data1.csv, data2.csv; Script: Get-ChildItem *.csv | Rename-Item -NewName { $_.Name.ToUpper() }

OutputFiles renamed to DATA1.CSV, DATA2.CSV

How to Think About It

To rename multiple files, first get the list of files you want to change using Get-ChildItem. Then, for each file, create a new name by adding or changing parts of the original name. Finally, use Rename-Item to apply the new name to each file.

Algorithm

1

Get the list of files matching a pattern or in a folder.

2

For each file, build the new file name based on the original name.

3

Rename the file using the new name.

4

Repeat until all files are renamed.

Code

powershell

Get-ChildItem -Path . -Filter *.txt | ForEach-Object {
    $newName = "new_" + $_.Name
    Rename-Item -Path $_.FullName -NewName $newName
    Write-Output "Renamed '$($_.Name)' to '$newName'"
}

Output

Renamed 'file1.txt' to 'new_file1.txt'
Renamed 'file2.txt' to 'new_file2.txt'
Renamed 'notes.txt' to 'new_notes.txt'

Dry Run

Let's trace renaming 'file1.txt' to 'new_file1.txt' through the code

1

Get files

Files found: file1.txt, file2.txt, notes.txt

2

Create new name

For file1.txt, newName = 'new_' + 'file1.txt' = 'new_file1.txt'

3

Rename file

Rename file1.txt to new_file1.txt

Original Name	New Name
file1.txt	new_file1.txt
file2.txt	new_file2.txt
notes.txt	new_notes.txt

Why This Works

Step 1: Get-ChildItem lists files

Get-ChildItem finds all files matching the pattern, like '*.txt', so you only rename the right files.

Step 2: Create new file names

Inside ForEach-Object, you build a new name by adding 'new_' before the original file name using string concatenation.

Step 3: Rename files

Rename-Item changes the file name on disk to the new name you created.

Alternative Approaches

Using a numbered sequence

powershell

Get-ChildItem -Filter *.txt | ForEach-Object -Begin { $i=1 } -Process {
    $newName = "file_" + $i + $_.Extension
    Rename-Item $_.FullName -NewName $newName
    $i++
    Write-Output "Renamed to $newName"
}

Adds a number sequence to file names instead of prefix; useful for ordered renaming.

Using a CSV mapping file

powershell

$map = Import-Csv -Path 'rename_map.csv'
foreach ($entry in $map) {
    Rename-Item -Path $entry.OldName -NewName $entry.NewName
    Write-Output "Renamed $($entry.OldName) to $($entry.NewName)"
}

Renames files based on a CSV file with old and new names; good for custom renaming lists.

Complexity: O(n) time, O(1) space

Time Complexity

The script processes each file once, so time grows linearly with the number of files (O(n)).

Space Complexity

The script uses constant extra space, only storing temporary variables for each file (O(1)).

Which Approach is Fastest?

All approaches rename files one by one, so time is similar; using a CSV mapping adds overhead but allows custom names.

Approach	Time	Space	Best For
Prefix renaming	O(n)	O(1)	Simple bulk renaming with pattern
Numbered sequence	O(n)	O(1)	Ordered renaming with numbers
CSV mapping	O(n)	O(n)	Custom renaming from external list