Tente isto:
#!/bin/bash
echo CPU: 'top -b -n1 | grep "Cpu(s)" | awk '{print $2 + $4}''
FREE_DATA='free -m | grep Mem'
CURRENT='echo $FREE_DATA | cut -f3 -d' ''
TOTAL='echo $FREE_DATA | cut -f2 -d' ''
echo RAM: $(echo "scale = 2; $CURRENT/$TOTAL*100" | bc)
echo HDD: 'df -lh | awk '{if ($6 == "/") { print $5 }}' | head -1 | cut -d'%' -f1'
Editar:
[root@dev ~]# df -lh
Filesystem Size Used Avail Use% Mounted on
/dev/mapper/vg_dev-lv_root
64G 31G 30G 51% /
tmpfs 1004M 112K 1004M 1% /dev/shm
/dev/sda1 485M 30M 430M 7% /boot
[root@dev ~]# top -b -n1
top - 13:39:49 up 8 days, 4:59, 3 users, load average: 0.00, 0.01, 0.00
Tasks: 135 total, 1 running, 134 sleeping, 0 stopped, 0 zombie
Cpu(s): 1.2%us, 0.5%sy, 0.0%ni, 98.0%id, 0.3%wa, 0.0%hi, 0.0%si, 0.0%st
Mem: 2055668k total, 1957592k used, 98076k free, 155640k buffers
Swap: 4128760k total, 83644k used, 4045116k free, 718168k cached
PID USER PR NI VIRT RES SHR S %CPU %MEM TIME+ COMMAND
1250 root 20 0 15028 1080 808 R 5.5 0.1 0:00.04 top
1 root 20 0 19336 1176 976 S 0.0 0.1 0:01.80 init
2 root 20 0 0 0 0 S 0.0 0.0 0:00.00 kthreadd
3 root RT 0 0 0 0 S 0.0 0.0 0:00.00 migration/0
4 root 20 0 0 0 0 S 0.0 0.0 0:00.00 ksoftirqd/0
5 root RT 0 0 0 0 S 0.0 0.0 0:00.00 watchdog/0
6 root 20 0 0 0 0 S 0.0 0.0 0:00.15 events/0
7 root 20 0 0 0 0 S 0.0 0.0 0:00.00 cpuset
8 root 20 0 0 0 0 S 0.0 0.0 0:00.00 khelper
9 root 20 0 0 0 0 S 0.0 0.0 0:00.00 netns
10 root 20 0 0 0 0 S 0.0 0.0 0:00.00 async/mgr
11 root 20 0 0 0 0 S 0.0 0.0 0:00.00 pm
12 root 20 0 0 0 0 S 0.0 0.0 0:00.00 sync_supers
13 root 20 0 0 0 0 S 0.0 0.0 0:00.00 bdi-default
14 root 20 0 0 0 0 S 0.0 0.0 0:00.00 kintegrityd/0
15 root 20 0 0 0 0 S 0.0 0.0 0:00.45 kblockd/0
16 root 20 0 0 0 0 S 0.0 0.0 0:00.00 kacpid
17 root 20 0 0 0 0 S 0.0 0.0 0:00.00 kacpi_notify
18 root 20 0 0 0 0 S 0.0 0.0 0:00.00 kacpi_hotplug
19 root 20 0 0 0 0 S 0.0 0.0 4:02.29 ata/0
20 root 20 0 0 0 0 S 0.0 0.0 0:00.00 ata_aux
21 root 20 0 0 0 0 S 0.0 0.0 0:00.00 ksuspend_usbd
22 root 20 0 0 0 0 S 0.0 0.0 0:00.00 khubd
23 root 20 0 0 0 0 S 0.0 0.0 0:00.00 kseriod
25 root 20 0 0 0 0 S 0.0 0.0 0:00.00 khungtaskd
26 root 20 0 0 0 0 S 0.0 0.0 0:07.66 kswapd0
27 root 25 5 0 0 0 S 0.0 0.0 0:00.00 ksmd
28 root 39 19 0 0 0 S 0.0 0.0 0:06.30 khugepaged
29 root 20 0 0 0 0 S 0.0 0.0 0:00.00 aio/0
30 root 20 0 0 0 0 S 0.0 0.0 0:00.00 crypto/0