awk使用简介：
awk 'BEGIN{statements} pattern{commands} END{ end statements}'
awk脚本包括三个部分：BEGIN+可以使用模式匹配的通用语句块+END语句块
执行步骤：
1.执行begin部分
2.读取input stream，每读一行数据，执行一次pattern部分
3.stream读完后执行end
例如：
[root@TopInsight 3760_04_code]#awk 'BEGIN {i=0} {i++} END{print i}' word_freq.sh
17
或者
[root@TopInsight 3760_04_code]#awk "BEGIN {i=0} {i++} END{print i}" word_freq.sh
17
示例1：打印.history_profile文件中中使用次数较多的命令
[root@Moneytu /var/log/httpd]# printf "%-20s Count
" Commands;cat ~/.bash_history | grep -Ev '#.*' | awk 'BEGIN {} {list[$1]++;}
> END { for(i in list)
> {
> printf("%-20s %d
",i,list[i]);}
> }' v1="Commands" v2="Count" | sort -nrk 2 | head
Commands Count
ls 151
cd 92
service 83
top 77
vi 72
df 63
mysql 47
mysqlcheck 40
iptables 39
tail 36
示例2：对apache访问ip进行排序，比较性能：
[root@Moneytu /var/log/httpd]# cat sum_ip.sh
#!/bin/bash
##对访问ip进行排序
useage(){
cat << EOF
$0 filename topN
EOF
exit 1
}
if [ $# -ne 2 ]; then
useage
fi
sumip(){
printf "%-20s Count
------------------------------
" IP;
awk 'BEGIN {FS=" ";}{IP[$1]++;}
END {for(i in IP)
{printf("%-20s %d
",i,IP[i]);}
}' $1 | sort -nrk 2 | head -n $TOP
}
FILE=$1
TOP=$2
sumip $FILE $TOP
结果：
[root@Moneytu /var/log/httpd]# time ./sum_ip.sh access_log 20 IP Count ------------------------------ 222.223.40.185 19787 60.28.116.222 17468 112.124.26.17 13891 ::1 13426 111.162.65.49 10201 61.183.230.130 9926 219.140.149.244 8891 113.247.155.122 8023 218.106.119.137 7776 61.189.184.55 6532 218.69.24.74 5931 220.181.125.198 5665 221.226.105.178 5115 123.126.68.36 4655 182.87.49.132 4620 113.116.173.16 4428 122.96.24.195 3878 60.166.75.85 3557 183.54.191.41 3399 222.88.66.49 3004 real 0m0.400s user 0m0.347s sys 0m0.056s
比下面的命令要快很多：
[root@Moneytu /var/log/httpd]# time cat access_log | awk '{print $1}' | sort | uniq -c | sort -nr | head -n 20
19787 222.223.40.185
17468 60.28.116.222
13862 112.124.26.17
13422 ::1
10201 111.162.65.49
9926 61.183.230.130
8891 219.140.149.244
8023 113.247.155.122
7776 218.106.119.137
6532 61.189.184.55
5931 218.69.24.74
5650 220.181.125.198
5115 221.226.105.178
4642 123.126.68.36
4620 182.87.49.132
4428 113.116.173.16
3878 122.96.24.195
3557 60.166.75.85
3399 183.54.191.41
3004 222.88.66.49
real 0m4.052s
user 0m3.823s
sys 0m0.237s
awk引用外部变量的方法：
for f in `ls`;do cat $f | awk '{print $1 >> "'$f.file'" }';done