Saturday, May 24, 2008

Okay, so let's try to start rewriting some CMD.EXE skillsets in Powershell. Here's something common: ping a range of subnets to see if the hosts are up and what their latency is. In CMD exe we first need some to code to produce an accurate timestamp because there is no native way to do this. Thus this complicated and idiosyncratic use of the set command to parse out time/date stamps:

:: realtd.cmd
@echo off

set realdate=%date:/=.%
set realdate=%realdate:* =%
set realtime=%time::=.%
set timestamp=%realdate%_%realtime%

Now we need some nearly unreadable spew, some help fron gawk, some hard coded ping options, a hard coded subnet range...:

:: TestSubnet.cmd
@echo off
set ThreeOctets=%1
for /l %%i in (1,1,255) do set #=%%i && call :label
goto EOF
:label @(call realtd)
@(ping -l 1 -n 1 -w 2 %ThreeOctets%.%#% | findstr Reply | gawk '{print "%timestamp%" ":" $1 ":" $3$5}' )


and last we can put a collection of the first three octects into text file and call them like this:

for /f %i in (subnets) do call Testsubnet %i

This gives us some reasonably parseable output:

D:\>call Testsubnet 193.0.0
05.24.2008_19.43.04.01:Reply: 05.24.2008_19.43.05.51:Reply: 05.24.2008_19.43.06.01:Reply: 05.24.2008_19.43.07.01:Reply:

D:\>call Testsubnet 194.0.0 05.24.2008_19.43.40.01:Reply:

Okay, so you can see quite a bit of inelegance here to start with. Let's list some issues:

(1) a separate cmd file needs to run each time to log the timestamp
(2) the ping options are hardcoded...that probably could be fixed...but more inelegance
(3) we don't really need the field 'Reply' or 'time='. but they are hard to parse out. Once again more awk or perl code would probably do this but at what cost of complexity
(4) I don't really want to have to call the file that calls THE file...I just want to point to an XML file with all the correct options....
(5) requires Cygwin or GNU-Win32 gawk in your path....

I could go on, but you get the picture. Let's assemble this tool with less complexity, more readability and more functionality in Powershell in the next post...

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