linux man for awk

处理文本时常有头和尾的处理需求，也有逻辑的使用，简单介绍如下

1，awk之 BEGIN 与END

BEGIN 用于需要在文本行轮询前的任务执行，END用于文档沦陷完成后的任务执行

例 找到所有bash用户，开头打印名称列，结尾打印end,并且显示每行的1，3，7列都执行左对齐，每列占10个字符的位置

linux-SUSE:/home/test # awk -F: 'BEGIN{print "UserName ID Shell"}$7~"bash"{printf "%-10s%-10s-%20s\n",$1,$3,$7}END{print "End of report."}' /etc/passwd
UserName ID Shell
at 25 - /bin/bash
bin 1 - /bin/bash
daemon 2 - /bin/bash
ftp 40 - /bin/bash
games 12 - /bin/bash
lp 4 - /bin/bash
man 13 - /bin/bash
news 9 - /bin/bash
nobody 65534 - /bin/bash
root 0 - /bin/bash
uucp 10 - /bin/bash
openlinux 1000 - /bin/bash
postgres 26 - /bin/bash
End of report.

2，awk 之 if-else 判断

例 判断文件中用户名为 root，打印列admin， 否则打印列 Common User

awk -F: 'BEGIN{print "UserName UserType"}{if ($1=="root") printf "%-15s: %s\n", $1,"Admin";else printf "%-15s: %s\n", $1, "Common User"}' /etc/passwd
UserName UserType
at             : Common User
avahi          : Common User
avahi-autoipd  : Common User
bin            : Common User

3，awk 之while 循环，

awk本身就是对文档的每一行进行遍历，while是遍历每一个字段

linux-SUSE:/home/test # awk -F: '{i=1;while (i<=NF) {if (length($i)>=4){print $i};i++}}' /etc/passwd
Batch jobs daemon
/var/spool/atjobs
/bin/bash

4，awk 之for ，

awk -F: ‘{for (i=1;i<=NF;i++) {if length($i)>=4 {print $i}}}' /etc/passwd

使用for循环实现上面的列子

awk -F: '{for (i=1;i<=NF;i++) {if (length($i)>=4) {print $i}}}' /etc/passwd
Batch jobs daemon
/var/spool/atjobs
/bin/bash
avahi
User for Avahi
/run/avahi-daemon

例如 awk 用for 处理统计tcp链接状态，并分开显示

linux-SUSE:/home/test # netstat -tan #显示当前所有tcp链接及状态
Active Internet connections (servers and established)
Proto Recv-Q Send-Q Local Address Foreign Address State
tcp 0 0 0.0.0.0:22 0.0.0.0:* LISTEN
tcp 0 0 127.0.0.1:631 0.0.0.0:* LISTEN
tcp 0 0 127.0.0.1:25 0.0.0.0:* LISTEN
tcp 0 0 172.18.107.223:22 172.18.107.217:51520 ESTABLISHED
tcp 0 0 :::22 :::* LISTEN
tcp 0 0 ::1:631 :::* LISTEN
tcp 0 0 ::1:25 :::* LISTEN
linux-SUSE:/home/test # netstat -tan | wc -l
9
linux-SUSE:/home/test # netstat -tan | awk '/^tcp/{STATE[$NF]++}END{for (i in STATE) {print i, STATE[i]}}'
LISTEN 6
ESTABLISHED 1

 文本分析统计

awk 统计文本日志中某个ip出现的次数

linux-SUSE:/home/test # awk '{count[$1]++}END{for (ip in count){printf "%-20s:%d\n",ip,count[ip]}}' ips.log
                    :1
IOError :1
192.168.0.1 :12
192.168.0.10 :1
192.168.0.2 :2
192.168.0.20 :1
192.168.0.11 :1