Filtering Specific Columns with cut
When working with text files, it can be useful to filter out specific fields. Imagine that you need to see a list of all users in the /etc/passwd file. In this file, several fields are defined, of which the first contains the name of the users who are defined. To filter out a specific field, the cut command is useful. To do this, use the -d option to specify the field delimiter（-d参数指定分隔符） followed by -f with the number of the specific field you want to filter out（-f参数指出你要过滤哪一个fields）. So, the complete command is cut -d : -f 1 /etc/passwd if you want to filter out the first field of the /etc/passwd file. You can see the result bellow:
[root@rhel7 ~]# cat /etc/passwd
root:x:0:0:root:/root:/bin/bash
bin:x:1:1:bin:/bin:/sbin/nologin
daemon:x:2:2:daemon:/sbin:/sbin/nologin
adm:x:3:4:adm:/var/adm:/sbin/nologin
lp:x:4:7:lp:/var/spool/lpd:/sbin/nologin
sync:x:5:0:sync:/sbin:/bin/sync
shutdown:x:6:0:shutdown:/sbin:/sbin/shutdown
halt:x:7:0:halt:/sbin:/sbin/halt
mail:x:8:12:mail:/var/spool/mail:/sbin/nologin
operator:x:11:0:operator:/root:/sbin/nologin
games:x:12:100:games:/usr/games:/sbin/nologin
ftp:x:14:50:FTP User:/var/ftp:/sbin/nologin
nobody:x:99:99:Nobody:/:/sbin/nologin
avahi-autoipd:x:170:170:Avahi IPv4LL Stack:/var/lib/avahi-autoipd:/sbin/nologin
systemd-bus-proxy:x:999:997:systemd Bus Proxy:/:/sbin/nologin
systemd-network:x:998:996:systemd Network Management:/:/sbin/nologin
dbus:x:81:81:System message bus:/:/sbin/nologin
polkitd:x:997:995:User for polkitd:/:/sbin/nologin
tss:x:59:59:Account used by the trousers package to sandbox the tcsd daemon:/dev/null:/sbin/nologin
postfix:x:89:89::/var/spool/postfix:/sbin/nologin
sshd:x:74:74:Privilege-separated SSH:/var/empty/sshd:/sbin/nologin
rusky:x:1000:1000:rusky:/home/rusky:/bin/bash
[root@rhel7 ~]# cut -d : -f 1 /etc/passwd --以冒号为分隔，filter第一部分
root
bin
daemon
adm
lp
sync
shutdown
halt
operator
games
ftp
nobody
avahi-autoipd
systemd-bus-proxy
systemd-network
dbus
polkitd
tss
postfix
sshd
rusky
[root@rhel7 ~]#
或者以冒号为分隔，filter第二部分结果如下：
[root@rhel7 ~]# cut -d : -f 2 /etc/passwd
x
x
x
x
x
x
x
x
x
x
x
x
x
x
x
x
x
x
x
x
x
x