BASH Script Performace

Today we will look at some bash code snippests and the performance issues. Lets first look at the problem and the implemented solution:

Problem: We needed to log the output of the ps command for all the process’s. This was required to be done on per minute basis and the output was required in comma separated files. So, here is what was implemented:

pslog=`ps -e -opid,ppid,user,nlwp,pmem,vsz,rss,s,time,stime,pri,nice,pcp:u,args|grep -v PID|sort -r -k 13,13`
        OLD_IFS=$IFS
        IFS=$'\n'
        logarr=( $pslog )
        for LOGLINE in ${logarr[@]}
        do
                LOGLINE=`echo $LOGLINE|awk '{OFS=",";print $1,$2,$3,$4,$5,$6,$7,:$8,$9,$10,$11,$12,$13,$14}'`
                echo $LOGLINE >> output
        done
        IFS=$OLD_IFS

This was working well and there were no issues. But suddenly we started seeing issues with the reported CPU usages. We would see that whenever this script was running the CPU usage was high, specially if there were too many process’s/thread’s on the system during that time.  This code was definitely part of a very large code base, and at this point of time we did not know what was causing the issues.