The awk command is used to only display certain fields of output. In this context, a field is a string of data, delimited by whitespace. For example, the df -h command has fields of data delimited by whitespace.

Piping the output to awk '{print}' produces the same exact output.

[root@server1 ~]# df -h | awk '{print}'
Filesystem     Size    Used    Avail    Use%    Mounted on
/dev/md127     1.8T    1.1T     604G     65%    /
/dev/sda1      488M    100M     354M     22%    /boot

gsub can be used to do a regular expression replacement. In this example, "dev" will be replaced with "bar" and $0 is used to only return the results that were modified.

]$ df -h | awk 'gsub("dev", "bar", $0)'
bartmpfs                          3.7G     0  3.7G   0% /bar
tmpfs                             3.7G     0  3.7G   0% /bar/shm
/bar/mapper/centos_ansible1-root   50G  9.2G   41G  19% /
/bar/mapper/centos_ansible1-home   54G  1.6G   53G   3% /home
/bar/sda1                         497M  168M  330M  34% /boot

1 can be included to return all results, both those that were modified and those that were not modified.

]$ df -h | awk 'gsub("dev", "bar", $0) 1'
Filesystem                        Size  Used Avail Use% Mounted on
bartmpfs                          3.7G     0  3.7G   0% /bar
tmpfs                             3.7G     0  3.7G   0% /bar/shm
tmpfs                             3.7G  382M  3.3G  11% /run
tmpfs                             3.7G     0  3.7G   0% /sys/fs/cgroup
/bar/mapper/centos_ansible1-root   50G  9.2G   41G  19% /
/bar/mapper/centos_ansible1-home   54G  1.6G   53G   3% /home
/bar/sda1                         497M  168M  330M  34% /boot
tmpfs                             751M     0  751M   0% /run/user/1000