harkcom@potato.pa.Yokogawa.CO.JP (Alton Harkcom) (07/07/90)
I don't understand...
I used a textbook example from Kernighan and Pike "The UNIX Programming
Environment" and then hit it with grep and it bellied up...
#sentry program to let me know when somebody logs on or off
#from page 147 "The UNIX Programming Environment" by Kernighan and Pike
# watchwho: watch who logs in and out
#PATH=/bin:/usr/bin # I don't need it
new=/tmp/wwho1.$$
old=/tmp/wwho2.$$
>$old # create empty file
while : # loop forever
do
who >$new
diff $old $new
mv $new $old
sleep 60
done | awk '/>/ && !/harkcom/ { $1 = "in: "; print }
/</ && !/harkcom/ { $1 = "out: "; print }'
#end
I typed "sentry &" (after setting it up) and it worked fine...
Today I decided I was tired of seeing my own name appear every time I opened
a new window in X. I typed "sentry | grep -v harkcom &" and I got nothing. I
logged in and out as other users many times (staying on for 2-3 minutes each
time) yet nothing came out.
I put grep directly after awk:
done | awk '/>/ && !/harkcom/ { $1 = "in: "; print }
/</ && !/harkcom/ { $1 = "out: "; print }' | grep -v harkcom
but no output. Then I took out awk and left grep. I got the diff lines for
the other users as expected. I then returned it to its original form and tried
it as usual. Again no problems. Then I tried "sentry > /tmp/sentry.tmp" and let
it run while I rlogged in and out on another terminal for a while. Then I
interrupted sentry and looked at /tmp/sentry.tmp. It was empty...
Is there something about the way that awk buffers that I need to know?
I fixed the problem by adding the awk script to skip my name but I still
want to know ?why?
Help...
--
--harkcom@potato.pa.yokogawa.co.jp