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/passwdroot:x:0:0:root:/root:/bin/bashbin:x:1:1:bin:/bin:/sbin/nologindaemon:x:2:2:daemon:/sbin:/sbin/nologinadm:x:3:4:adm:/var/adm:/sbin/nologinlp:x:4:7:lp:/var/spool/lpd:/sbin/nologinsync:x:5:0:sync:/sbin:/bin/syncshutdown:x:6:0:shutdown:/sbin:/sbin/shutdownhalt:x:7:0:halt:/sbin:/sbin/haltmail:x:8:12:mail:/var/spool/mail:/sbin/nologinoperator:x:11:0:operator:/root:/sbin/nologingames:x:12:100:games:/usr/games:/sbin/nologinftp:x:14:50:FTP User:/var/ftp:/sbin/nologinnobody:x:99:99:Nobody:/:/sbin/nologinavahi-autoipd:x:170:170:Avahi IPv4LL Stack:/var/lib/avahi-autoipd:/sbin/nologinsystemd-bus-proxy:x:999:997:systemd Bus Proxy:/:/sbin/nologinsystemd-network:x:998:996:systemd Network Management:/:/sbin/nologindbus:x:81:81:System message bus:/:/sbin/nologinpolkitd:x:997:995:User for polkitd:/:/sbin/nologintss:x:59:59:Account used by the trousers package to sandbox the tcsd daemon:/dev/null:/sbin/nologinpostfix:x:89:89::/var/spool/postfix:/sbin/nologinsshd:x:74:74:Privilege-separated SSH:/var/empty/sshd:/sbin/nologinrusky: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rootbindaemonadmlpsyncshutdownhaltmailoperatorgamesftpnobodyavahi-autoipdsystemd-bus-proxysystemd-networkdbuspolkitdtsspostfixsshdrusky[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  xxxxxxxxxxxxxxxxxxxxxx