awk useful commands examples

awk useful comand examples. How to Output Field Separator Variable, Number of Fields in a record, To print Non-system users and ignoring "nobody" etc. 

You may reading link below :

• How to reset root password on centos 7
• CentOS/RHEL Use yum Command To Downgrade Upgrade or Rollback Updates
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• use inotify-tools on centos

For example, the output passwd file use awk command

$ cat /etc/passwd | awk -F':' 'BEGIN{ print "Name\tUID,GID\tHomeDirectory" }{print $1"\t"$3,$4"\t"$6}'

The output as below:

Name UID,GID HomeDirectory
root 0 0 /root
bin 1 1 /bin
daemon 2 2 /sbin
adm 3 4 /var/adm
lp 4 7 /var/spool/lpd
sync 5 0 /sbin
shutdown 6 0 /sbin
halt 7 0 /sbin
mail 8 12 /var/spool/mail
operator 11 0 /root
games 12 100 /usr/games
ftp 14 50 /var/ftp
nobody 99 99 /
systemd-bus-proxy 999 998 /
systemd-network 192 192 /
dbus 81 81 /
polkitd 998 997 /
tss 59 59 /dev/null
sshd 74 74 /var/empty/sshd
postfix 89 89 /var/spool/postfix
dockerroot 997 994 /var/lib/docker
huupv 1000 1000 /home/huupv

Awk OFS Example: Output Field Separator Variable

By default awk OFS is a single space character. How to use OFS assgin a single space character equal to ',' as below:

$ cat /etc/passwd | awk -F':' 'BEGIN{{OFS=","} print "Name\tUID,GID\tHomeDirectory" }{print $1"\t"$3,$4"\t"$6}'

The output as below:

Name UID,GID HomeDirectory
root 0,0 /root
bin 1,1 /bin
daemon 2,2 /sbin
adm 3,4 /var/adm
lp 4,7 /var/spool/lpd
sync 5,0 /sbin
shutdown 6,0 /sbin
halt 7,0 /sbin
mail 8,12 /var/spool/mail
operator 11,0 /root
games 12,100 /usr/games
ftp 14,50 /var/ftp
nobody 99,99 /
systemd-bus-proxy 999,998 /
systemd-network 192,192 /
dbus 81,81 /
polkitd 998,997 /
tss 59,59 /dev/null
sshd 74,74 /var/empty/sshd
postfix 89,89 /var/spool/postfix
dockerroot 997,994 /var/lib/docker
huupv 1000,1000 /home/huupv

Awk NF NR Example: Number of Fields in a record

Awk NF gives you the total number of fields in a record
Awk NR gives you the total number of records being processed or line number

$ cat huuphan-awk

The output as below:

huu 213 78 84 77
phan 221 56 58 45 111
huuphan 222 138 37 31
huuphan.com 257 178 67 45 333

$ awk '{print "line "NR,"->",NF"(Fields)"}' huuphan-awk

The output as below:

line 1 -> 5(Fields)
line 2 -> 6(Fields)
line 3 -> 5(Fields)
line 4 -> 6(Fields)

To print Non-system users and ignoring "nobody"

$ getent passwd |awk -F : '$3 >= 1000 && $3 < 65534' | awk -F':' 'BEGIN{{OFS=","} print "Name\tUID,GID\tHomeDirectory" }{print $1"\t"$3,$4"\t"$6}'

The output as below:

Name UID,GID HomeDirectory
huupv 1000,1000 /home/huupv