Re: Specifying multiple separators via FS or the -F command line flag

[Bob Proulx]

cga2000 wrote:
> backtick 4 0  0  awk -F "[: ]" 'BEGIN                              \
> {file="/proc/net/dev";while(a==a){while(getline<file!=0){if        \
> ($3=="eth0"){d=$4;u=$12;printf " %4.1f k/s ",((d-dp)/1024);printf  \
> "%4.1f k/s\n",((u-up)/1024)}};close(file);dp=d;up=u;system("sleep  \
> 1")}}'

Oh, gosh, that is hard to read!  But of course you already knew that. :-)

> NB. I do realize that when one-liners get to be this long it's probably
>     time to move them to a file :-)

Yes.

>     lo:649004371  349860    0    0    0     0          0         
>   eth0:673423996 22297294  789    0 1100   789          0     <-
> When I bring up the interface the byte counter is separated from
> field "eth0:" by a number of spaces.
> After a while as the value become larger, and eventually all the
> spaces disappear to make room for the increased number of bytes.

I tend to pre-process these cases to guarantee space separation.

  line=' eth0:673423996 22297294  789    0 1100   789          0'
  echo "$line" | awk '{sub(/(eth[[:digit:]]|lo):/,"& ");print $2}'
  673423996

  line='  lo:649004371  349860    0    0    0     0          0'
  echo "$line" | awk '{sub(/(eth[[:digit:]]|lo):/,"& ");print $2}'
  673423996

I would try that technique.  Here I have used an ERE to match either
of the cases presented.  It is still not very general though.  I would
tend to get the list of devices dynamically.

I don't know if this is a great way to do this but so far I have
noticed that every type of system I have tried reports header lines in
capital letters.  I can use this to detect which lines are device
lines.

  netstat -ni | awk '/^[[:lower:]]/{print$1}' | sort -u
  eth1
  eth2
  lo

I would probably use that to build the match regular expression.  But
I will leave that as an exercise for the reader.  :-)

> I thought I'd use the above to illustrate my problem rather than a test
> file as Bob Proulx suggested in his reply to my initial post in the
> bug-gnu-utils list because I have no knowledge of awk apart from reading
> through an online tutorial a couple of months ago and I might have made
> some assumptions that would have confused the issue further.

But the full case is often very intimidating.  That big block of awk
one-liner is too dense.  It scares people off.

I would tend not to use "only" awk here.  My own preference is to use
shell scripts and use awk in pieces.  Also, instead of parsing /proc I
would use netstat because it is more portable.  I am not going to
finish this off but you can see where I am going with this:

  netstat -ni | awk '/^[[:lower:]]/{print$1,$4}'

Hope that helps,
Bob