Re: Please advise on programming tactics/strategy

[Matthew Woehlke]

cga2000 wrote:
> I was wondering if there is any way I can convince netstat to return
> its output to bash variables for processing.
>
> Pretty simple logic:
>
> Do forever:
>
>   Call netstat to obtain RX & TX byte counts 
>   Print delta {current .. minus previous .. byte counts}
>   Save current byte counts 
>   Wait for a second or so ..
>
> I initially thought I could just pipe the "netstat -in" command to the
> invocation of a bash function.
>
> The function would have taken care of the gory details of parsing &
> formatting the output of the netstat command and would then have stored
> the current byte counts where they would be available for the next time
> the function is invoked.
>
> The trouble is that I haven't been able to find anything like a "static"
> local variable that is not reinitialized every time the function is
> invoked.

Pipes run as seperate processes, e.g. in 'somecommand | function', 
'function' is run as a subshell, so anything done in 'function' does not 
propagate up to the parent. You might want to look at bash's command 
redirection instead.

Alternatively, something like 'foo=$(netstat | extract)' where 'extract' 
filters the netstat output and condenses it down to something more 
easily parsed in the parent, e.g. 'TX:RX'. Then you can do something 
like 'tx=${foo%:*}; rx=${foo#*:}'.

--
Matthew
"Who wants to sing?" -- Orcs (Warcraft II)