[lug] Bash Scripting Ping

[Chan Kar Heng]

How's Jed's suggestion different from what you need?

Best regards,
kh


On 9 November 2020 02:27:21 GMT+08:00, "D. Stimits" <stimits at comcast.net> wrote:
>
>> On 11/08/2020 11:21 AM Jed S. Baer <blug at jbaer.cotse.net> wrote:
>> 
>>  
>> On Sun, 8 Nov 2020 10:53:09 -0700 (MST)
>> D. Stimits wrote:
>> 
>> > I am curious about something in bash scripting which does not seem
>to be
>> > particularly easy. I wanted to script "ping -O -D address" such
>that each
>> > line gets processed by some logic if the ping fails. Redirecting
>ping to
>> > a variable does not work because it only "returns" when the ping
>exits
>> > (each line is not an exit). Even if I were to fork and exec, the
>forked
>> > process would itself have the same problem.
>> > 
>> > Is there some simple/clever way to process each line of a ping in
>bash
>> > without killing off the ping itself? My goal was to send it through
>some
>> > database and statistics type processing as success/failure lines
>occur.
>> 
>> I'm not sure of quite what you want. Is it necessary to process this
>in
>> real time? And you say "...if ping fails", but then "... as
>success/failure
>> lines occur."
>
>I'd like to know if there is a way to pipe the output of ping such that
>each line is equivalent to a loop iteration. Pseudo code:
>   while (ping text line); do
>      line | edit line; # e.g., substituting microseconds for date.
>print edit line if conditions are met; # e.g., a few lines of fail
>prior to print.
>   done
>
>I'm not actually concerned that this is ping so much as I am trying to
>figure out how a newline from a continuous command can be used to
>trigger a loop iteration. It has become something of a "brain teaser"
>for me. It is easy if the ping itself ends with a single ping. It is
>also easy if you run ping all day and only then process the results
>upon exit of ping. I am now just really curious how the newline
>delimited continuous output of ping can be used to trigger something
>else despite the continuous output itself not stopping.
>
>> 
>> The super simple thing is a bash read loop. But you won't know the
>exit
>> status until the ping finishes.
>> 
>> $ ping -c 3 -D -O n.n.n.n | while read LINE;
>> > do
>> > echo $LINE
>> > done
>> 
>> Bash read will do token separation using IFS, so you could do
>>   | while read FIELD1 FIELD2 etc
>> 
>> Offhand, if the exit status of ping must be known before processing,
>then
>> redirect ping output to a file, check status, then you can still do a
>bash
>> read loop to process the file. If needed, the bash mktemp command
>will
>> generate a unique tmp filename for your ping output.
>> 
>> -- 
>> All operating systems suck, but Linux just sucks less
>>  - Linus Torvalds
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