PowerShell to add date to all filenames in a folder

I have three files named First_File.txt Second_File.txt Thrid_File.txt in a folder named C:\01Source I want to add the current date to the filenames so they look like this: First_File_20220909.txt

The terminal output is this:

What if: Performing the operation "Rename File" on target "Item: C:\01Source\First_File.txt Destination: C:\01Source\First_File_20220909.txt". (runs for all three files names)

BUT... when I look in the C:\01Source folder the filenames are not changed, they are still First_File.txt

What did I miss?

This is my code:

$Path = "C:\01Source\"
write-host $Path
$curDateTime = Get-Date -Format yyyyMMdd
Get-ChildItem $Path -Recurse |
  Rename-Item -NewName {$_.Basename + '_' + $curDateTime + $_.Extension } -WhatIf

Solution

Abraham Zinala has provided the crucial pointer:

The -WhatIf common parameter in the command above only previews the operation without actually performing it.
- The purpose of using -WhatIf is to do a "dry run" that allows you to confirm that the command will work as intended when actually run, so as to prevent potentially costly mistakes.
That is, the message you saw, What if: Performing the operation "Rename File" on ..., tells you what would happen if you re-ran the command WITHOUT -WhatIf.
- Therefore, you simply need to remove -WhatIf from the end of your Rename-Item call in order to perform actual renaming.

Note that not all cmdlets support -WhatIf - generally only those with potentially destructive consequences.

Cmdlets that support -WhatIf also support the common -Confirm parameter (and vice versa), which requests that a per-input-object confirmation prompt be shown before processing.

To see whether a given cmdlet supports -WhatIf / -Confirm, look for [-WhatIf] / [-Confirm] in the syntax diagrams output by Get-Help or when you pass the -? switch, or when you use Get-Command -Syntax; e.g., Rename-Item -? or Get-Command -Syntax Rename-Item.
Alternatively, as you're typing a command, try tab completion (type something like -Wha, then press Tab to see if it auto-completes to -WhatIf).

It is possible to implement support for -WhatIf and -Confirm in your own functions and scripts, as long as they are advanced ones, as the following example shows:

function Remove-Foo {
  # * "SupportsShouldProcess" is what activates -WhatIf / -Confirm support.
  # * The "ConfirmImpact" value determines whether confirmation prompts are shown
  #   by default, relative to the $ConfirmPreference preference variable.
  #   Setting the value to 'High' would prompt *by default*.
  [CmdletBinding(SupportsShouldProcess, ConfirmImpact='Medium')]
  param(
    [Parameter(Mandatory, ValueFromPipeline)]
    [string]
    $FooId
  )

  process {
    # $PSCmdlet.ShouldProcess() either shows the conformation prompt (with -Confirm)
    # or prints a what-if message (with -WhatIf).
    # If $false is returned, the confirmation prompt was declined, or a what-if message was printed,
    # so no further action should be taken for this object.
    if ($false -eq $PSCmdlet.ShouldProcess($FooId)) {
      return # Do nothing (else)
    }
    # Regular processing.
    "Removing $FooId..."
  }

}

Sample call after defining the above function:

PS> 'foo', 'bar' | Remove-Foo -WhatIf
What if: Performing the operation "Remove-Foo" on target "foo".
What if: Performing the operation "Remove-Foo" on target "bar".