It is same as ms-dos command where.exe

where-command.ps1

function Where-command
{
    param(
        [Parameter(ValueFromPipeline=$true,Mandatory=$true)]
        [string]  $Name
    )
 
    begin
    {
    }
 
    process
    {
      $path = [environment]::GetEnvironmentVariable("PATH")
      $folders = $path.split(';')
      foreach($folder in $folders){
        $result = Join-Path $folder -ChildPath $Name | Test-Path
        if($result -eq $true){
          return $result
        }
      }
      return $false
    }
 
    end
    {
    }
}