Improving Batch File for loop with start subcommand

Question

I\'ve currently got a very simple script which pings 10 IPs:

@ECHO OFF
for /L %%i in (100, 1, 110) DO (
  START /W /B cmd /c ping -n 1 192.168.0.%%i | find \         


        

Answer 1

Asynchronous isn't easy, but with jobs you can get close pretty easily with PowerShell.

This code should behave how it looks like your bash code does, returning the IP address of all hosts that respond without error:

$IPAddresses = 100..110 | ForEach-Object { "192.168.0.$_"; }

$JobList = $IPAddresses | ForEach-Object {
    Test-Connection -ComputerName $_ -Count 1 -AsJob;
}

Receive-Job -Job $JobList -AutoRemoveJob -Wait | `
    Where-Object { $_.StatusCode -eq 0 } | `
    Select-Object -ExpandProperty Address;

The above completes for me against ~250 hosts in 3 seconds.

Test-Connection itself claims to use up to 32 simultaneous connections (configurable with -ThrottleLimit setting) but it sure seems like the -Delay option completely overrides that setting if you're targeting a wide range.

You may have issues with PowerShell v4 and earlier, as it may behave slightly differently. Test-Connection in particular seems to be idiosyncratic on different versions of Windows or PowerShell. At least, I always remember it throwing an error instead of returning an error status code in previous versions.

If you want more fine grain control over the ping than Test-Connection gives you -- for example, it defaults to a 1 second timeout so the minimum time you'll wait when any host is down is 1 second -- you'll probably have to revert to directly calling Get-WMIObject -Query "SELECT * FROM Win32_PingStatus WHERE Address = '$IP' AND TimeOut = 200" -AsJob.