PowerShell - Filter Versus Function

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Hello,

A filter is a ‘simplified’ function type that automatically uses the Process block (no Begin and End blocks) and therefore executes on every object.

A filter natively manages pipeline objects and performs a loop on each object.

# Explicit Process block
Function Test-Function {
    process { $_ }
}
# Implicit Process block
Filter Test-Filter { $_ }
# Behaviour check
1..3 | Test-Function
1..3 | Test-Filter

Filter is interesting for doing simple checks and actions on each object in the pipeline, for the rest use a function instead.

# Create a folder if it doesn't exist with Filter
Filter New-Folder
{
  if (!(Test-Path -Path $_ -PathType Container)) {
    New-Item -Path $_ -ItemType Directory
  }
}
c:\test','c:\test2' | New-Folder

# Create a folder if it doesn't exist with a function
Function New-Folder {
    process {
        if (!(Test-Path -Path $_ -PathType Container)) {
            New-Item -Path $_ -ItemType Directory
        }
    }
}
'c:\test3','c:\test4' | New-Folder