Shell Programming and Scripting

getFileSystemPerformanceData()
{


  if [ -r /etc/issue ] ; then
     if grep -q "Ubuntu" /etc/issue ; then
         CMD="df -lP | grep -v "\/home" | grep -v "\/dev/mapper/VolGroup-lv_root""
      elif grep -q "Mageia" /etc/issue; then
        CMD="df -lP | sed -e '2d'"
       elif grep -q "Fedora" /etc/issue; then
          CMD="df -lP | grep -v "\/home" | grep -v "\/dev/mapper/VolGroup-lv_root""
       else
       CMD="df -lP"
       fi
   else
  CMD="df -lP"
  fi
  OUTPUT=`$CMD`
    echo "$OUTPUT" |
    ( # Skip the header-line
        read IGNORED
        SUM=0
        SIZE=0
        while read FS SIZE USED AVAIL PCT MOUNTED ; do
            SIZE=`echo "$AVAIL 1024" | awk '{print $1/$2}'`
            SUM=`echo "$SUM $SIZE" | awk '{print $1 + $2}'`
        done
        PERFCLASS=LogicalDisk;PERFINSTANCE=$FS;PERFMETRIC='Avail Megabytes';PERFINT=0;PERFSAMP=1;PERFAVG=$SUM;PERFMIN=$PERFAVG;PERFMAX=$PERFAVG;writePerformanceDataXml
    )
    
}

bash -x ./yourscript

.
.
.
CMD="df -lP"
fi                    # from somewhere above
OUTPUT=`$CMD`         # assign literal $CMD to OUTPUT
echo "$OUTPUT" |      # echo $CMD literally - one word in one single line
read IGNORED          # ignore literal $CMD, input stream ends, skip loop
.
.
.

eval "$CMD" | ( # skip the header-line
    read IGNORED
    ...

df -lP | awk 'NR>1 {sum+=$4/1024} END {print sum}'
30569.2

Filesystem            Size  Used Avail Use% Mounted on
rootfs                9.0G  3.6G  4.9G  43% /
udev                  368M     0  368M   0% /dev
tmpfs                 375M  248K  375M   1% /dev/shm
tmpfs                 375M  552K  375M   1% /run
/dev/mapper/VolGroup-lv_root  9.0G  3.6G  4.9G  43% /
tmpfs                 375M     0  375M   0% /sys/fs/cgroup
tmpfs                 375M     0  375M   0% /media
/dev/sda1             485M   31M  430M   7% /boot
/dev/mapper/VolGroup-lv_root  9.0G  3.6G  4.9G  43% /tmp
/dev/mapper/VolGroup-lv_root  9.0G  3.6G  4.9G  43% /var/tmp
/dev/mapper/VolGroup-lv_root  9.0G  3.6G  4.9G  43% /home

[root@localhost ~]# df -lP | awk 'NR>1 {sum+=$4/1024} END {print sum}'
27220.8