Add Attachment to List Item in SharePoint using PowerShell

How to Add Attachment to a SharePoint List Item?
To add attachment to SharePoint list item,

• Navigate to the list, select a list item 
• Click on "Attach File" button from the "Items" tab of the ribbon. 
• Browse and select the file to attach. Click OK to attach the file to item. You can also Edit the list item and then attach file.
  

PowerShell to add attachment to sharepoint list item
Here is the PowerShell script to add attachment to list item programmatically in SharePoint

Add-PSSnapin Microsoft.SharePoint.PowerShell -ErrorAction SilentlyContinue

#Custom Function to Add attachment to SharePoint List Item
Function Add-Attachment($Item, $AttachmentPath)
{
  $FileContent = [System.IO.File]::ReadAllBytes($AttachmentPath)
  $Item.Attachments.Add([System.IO.Path]::GetFileName($AttachmentPath), $FileContent)
  $Item.Update()
 
  Write-host "Attachment Added to List Item Successfully!"
}

#Variables
$SiteURL="https://portal.crescent.com/sites/Deals"
$ListName="Tasks"
$ItemID=1
$AttachmentPath="c:\Scripts\ASI-LOG.docx"

$web = Get-SPWeb $SiteURL
$List = $web.Lists[$ListName]
$Item = $list.GetItemById($ItemID)

#Call the function to Add Attachment
Add-Attachment $Item $AttachmentPath

To add an attachment to SharePoint Online list item, use: SharePoint Online: Add Attachment to list item using PowerShell