对/etc/passwd文件的第三个字段以数值型排序

oracle@alicrm_test:/home/oracle>sort -t: -k3 -n /etc/passwd
root:x:0:0:root:/root:/bin/bash
tony.zhaoj:x:0:602::/root:/bin/bash
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
operator:x:11:0:operator:/root:/sbin/nologin
gopher:x:13:30:gopher:/var/gopher:/sbin/nologin
nscd:x:28:28:NSCD Daemon:/:/sbin/nologin
rpcuser:x:29:29:RPC Service User:/var/lib/nfs:/sbin/nologin
rpc:x:32:32:Portmapper RPC user:/:/sbin/nologin
netdump:x:34:34:Network Crash Dump user:/var/crash:/bin/bash
rpm:x:37:37::/var/lib/rpm:/sbin/nologin
ntp:x:38:38::/etc/ntp:/sbin/nologin
gdm:x:42:42::/var/gdm:/sbin/nologin
xfs:x:43:43:X Font Server:/etc/X11/fs:/sbin/nologin
mailnull:x:47:47::/var/spool/mqueue:/sbin/nologin
smmsp:x:51:51::/var/spool/mqueue:/sbin/nologin
pegasus:x:66:65:tog-pegasus OpenPegasus WBEM/CIM services:/var/lib/Pegasus:/sbin/nologin
haldaemon:x:68:68:HAL daemon:/:/sbin/nologin
vcsa:x:69:69:virtual console memory owner:/dev:/sbin/nologin
sshd:x:74:74:Privilege-separated SSH:/var/empty/sshd:/sbin/nologin
pcap:x:77:77::/var/arpwatch:/sbin/nologin
dbus:x:81:81:System message bus:/:/sbin/nologin
nobody:x:99:99:Nobody:/:/sbin/nologin
oracle:x:501:501:Oracle software owner:/home/oracle:/bin/bash
admin:x:505:505::/home/admin:/bin/bash
mysql:x:601:601:mysql software owner:/home/mysql:/bin/bash
nfsnobody:x:4294967294:4294967294:Anonymous NFS User:/var/lib/nfs:/sbin/nologin