linux awk

[root@k8s-node-01 zwf]# ll
total 505244
drwxrwxr-x 8 root root       191 Sep  1 08:45 eclipse
-rwxrwxrwx 1 root root 344056669 Sep  1 08:43 eclipse-jee-oxygen-3-linux-gtk-x86_64.tar.gz
drwxrwxrwx 7 root root       121 Sep  1 10:42 eclipse_workspace
drwxrwxrwx 8   10  143       255 Apr 11  2015 jdk1.8.0_45
-rwxrwxrwx 1 root root 173271626 Sep  1 08:26 jdk-8u45-linux-x64.tar.gz
-rw-r--r-- 1 root root     34023 Sep  1 10:57 zengwenfeng_hadoop.txt
[root@k8s-node-01 zwf]# 
[root@k8s-node-01 zwf]# 
[root@k8s-node-01 zwf]# 
[root@k8s-node-01 zwf]# 
[root@k8s-node-01 zwf]# free
              total        used        free      shared  buff/cache   available
Mem:        5178128     4213312      145584      304424      819232      365676
Swap:             0           0           0
[root@k8s-node-01 zwf]# 
[root@k8s-node-01 zwf]# free | awk '/Mem/{field $3}'
[root@k8s-node-01 zwf]# 
[root@k8s-node-01 zwf]# free | awk '/Mem/{print $3}'
4209796
[root@k8s-node-01 zwf]# 
[root@k8s-node-01 zwf]# free | awk '/Mem/{print $4}'
145148
[root@k8s-node-01 zwf]# 
[root@k8s-node-01 zwf]# 
[root@k8s-node-01 zwf]# 
[root@k8s-node-01 zwf]# df
Filesystem              1K-blocks     Used Available Use% Mounted on
devtmpfs                  2572168        0   2572168   0% /dev
tmpfs                     2589064        0   2589064   0% /dev/shm
tmpfs                     2589064   263892   2325172  11% /run
tmpfs                     2589064        0   2589064   0% /sys/fs/cgroup
/dev/mapper/centos-root  40137576 30959080   9178496  78% /
/dev/mapper/centos-home  19593216    37908  19555308   1% /home
/dev/sda1                 1038336   213076    825260  21% /boot
/dev/sr0                  4669162  4669162         0 100% /run/media/root/CentOS 7 x86_64
tmpfs                      517816       28    517788   1% /run/user/0
overlay                  40137576 30959080   9178496  78% /var/lib/docker/overlay2/c2b17bbce8881ca3d62248e2c09bbf0692c5d108f4c161f29948f1a6b258bd07/merged
shm                         65536        0     65536   0% /var/lib/docker/containers/66a8cb92961523bb02f974c4045889e3b43f74379d152041aa3b8e56ee7b0600/shm
overlay                  40137576 30959080   9178496  78% /var/lib/docker/overlay2/4ed8579835fa5c4132047551b5a48706563f6632a1c3d529bc1c2694bcbc9d78/merged
shm                         65536        0     65536   0% /var/lib/docker/containers/6ea3ce9e48b251247393b8f8a15c5a3d314f6c6057b4b8285fbfede26cabd9d4/shm
overlay                  40137576 30959080   9178496  78% /var/lib/docker/overlay2/6d5e1204d0abe9da16a493b17bf73a07226391f9bf1603b8ab6a42d9066b86f2/merged
shm                         65536        0     65536   0% /var/lib/docker/containers/241416027da3596b7d4fffb5df834394272338a8464834b2f4fc15144a5df9f0/shm
overlay                  40137576 30959080   9178496  78% /var/lib/docker/overlay2/fafb1447c532c17dcb688f58c841b20085b02f4e281e2de2888d7dae8a41da32/merged
shm                         65536        0     65536   0% /var/lib/docker/containers/1c8ee2959538109f6240e6520c24cc15fa1daa04a242a0949b8eb341f5225dae/shm
[root@k8s-node-01 zwf]# 
[root@k8s-node-01 zwf]# 
[root@k8s-node-01 zwf]# df /
Filesystem              1K-blocks     Used Available Use% Mounted on
/dev/mapper/centos-root  40137576 30959080   9178496  78% /
[root@k8s-node-01 zwf]# 
[root@k8s-node-01 zwf]# 
[root@k8s-node-01 zwf]# df / | awk '/\//{print $4}'
9178496
[root@k8s-node-01 zwf]# 
[root@k8s-node-01 zwf]#