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hack.augusto

Member

From: Brazil

Registered: 2008-08-28

Posts: 124

[solved]awk code work with files but not with standard output

my internet connection is unstable, then to know when the net is on/off i'm writing a script like that:

coproc ping -i 10 201.24.94.254 | awk '{print $NF}' > net_status
while :; do
   if [[ `cat /sys/class/net/eth0/operstate` == "down" ]] then
     print 'offline'
   elif [[ `cat net_status` == "unreachable" ]] then
     print 'on local net'
   else
     print 'on internet'
   fi
done

my problem is when i run this:

coproc ping -i 10 201.24.94.254 | awk '{print $NF}' > net_status

I get a blank net_status file "coproc ping -i 10 201.24.94.254 | awk '{print $NF > net_status}'" doesn't work also, right now the code is less or more like this:

coproc ping -i 10 201.24.94.254 > net
while :; do
 awk '{print $NF}' net > net_status || sed 1d net
...

but I would like to know why the first "way" doesn't work.

thanks

Last edited by hack.augusto (2008-10-30 21:11:30)

byte

Member

From: Düsseldorf (DE)

Registered: 2006-05-01

Posts: 2,046

Re: [solved]awk code work with files but not with standard output

What is coproc? Also post some sample output.

---

1000

hack.augusto

Member

From: Brazil

Registered: 2008-08-28

Posts: 124

Re: [solved]awk code work with files but not with standard output

What is coproc? Also post some sample output.

coproc establish a coprocess job. I use this because I want the script to run the while loop, and the ping process to continue running.

This is what I expected to be in the file:

$ ping 201.24.94.254 | awk '{print $NF}'                       
data.
ms
ms
ms
ms
...

But when I do this:

$ ping 201.24.94.254 | awk '{print $NF}' > net_stat

net_stat is just a blank file

$ cat net_stat

Procyon

Member

Registered: 2008-05-07

Posts: 1,819

Re: [solved]awk code work with files but not with standard output

Could it be the buffer is not full or did not reach EOF? Try letting it run to the end. ( Just my guess though, I've never used coproc)

hack.augusto

Member

From: Brazil

Registered: 2008-08-28

Posts: 124

Re: [solved]awk code work with files but not with standard output

Could it be the buffer is not full or did not reach EOF? Try letting it run to the end. ( Just my guess though, I've never used coproc)

That is exactly what is going on .

How could I simulate EOF to force awk to print the line in the file every time?

hack.augusto

Member

From: Brazil

Registered: 2008-08-28

Posts: 124

Re: [solved]awk code work with files but not with standard output

I found it:

ping 201.24.94.254 | awk -v nf="net_stat" '{print $NF > nf} {close(nf)}'

thanks for the help.