Originally published June 7, 2016 @ 11:34 am
Just a quick note on addressing a common issue of running redundant commands when using shell loops. Let’s say you needed to get a count of network connections to an Oracle database server for each connection state: established, close_wait, etc. Here’s one way of doing this:
for i in ESTABLISHED CLOSE_WAIT LISTEN IDLE BOUND
do
echo -e "${i}:\t`netstat -a | egrep "\.152[16].*${i}" | wc -l`"
done | column -t
This works just fine, but there is an issue of performance, since you’re running netstat five times. Of course, you can run netstat once, redirect output to a temporary file and then parse the file.
Perhaps an even better option is to use an array to store output of netstat. Note the use of IFS to properly store array values that contain spaces. Also note the printf syntax to output array values one per line.
IFS=$'\n' ; a=($(netstat -a | egrep "\.152[16]")) ; unset IFS
for i in ESTABLISHED CLOSE_WAIT LISTEN IDLE BOUND
do
echo -e "${i}:\t`printf '%s\n' \"${a[@]}\" | grep ${i} | wc -l`"
done | column -t
Experienced Unix/Linux System Administrator with 20-year background in Systems Analysis, Problem Resolution and Engineering Application Support in a large distributed Unix and Windows server environment. Strong problem determination skills. Good knowledge of networking, remote diagnostic techniques, firewalls and network security. Extensive experience with engineering application and database servers, high-availability systems, high-performance computing clusters, and process automation.
