1，多个动作，怎么写？

ghostwu@dev:~/linux/awk$ cat host.txt name    ip地址host1    192.168.1.1host2    192.177.81.1host3    10.0.0.5host4    192.168.3.98host5    192.168.3.98host6    192.168.9.254

每个{}表示一个动作：

ghostwu@dev:~/linux/awk$ awk '{print $1} {print $2}' host.txt nameip地址host1192.168.1.1host2192.177.81.1host310.0.0.5host4192.168.3.98host5192.168.3.98host6192.168.9.254

他的等价形式，这种方式更符合我们的编程习惯，一个语句，一个分号。

ghostwu@dev:~/linux/awk$ awk '{print $1; print $2}' host.txt nameip地址host1192.168.1.1host2192.177.81.1host310.0.0.5host4192.168.3.98host5192.168.3.98host6192.168.9.254

 请注意与这种方式的区别：

ghostwu@dev:~/linux/awk$ awk '{print $1, $2}' host.txt name ip地址host1 192.168.1.1host2 192.177.81.1host3 10.0.0.5host4 192.168.3.98host5 192.168.3.98host6 192.168.9.254

2，if语句

ghostwu@dev:~/linux/awk$ cat ghostwu.txt ghostwu 20 manzhangsan 22lisighostwu 30 manzhanzhao 40 manpeter 20 manzhanzhao 30 man

ghostwu@dev:~/linux/awk$ awk '{ if(NR == 1){ print }}' ghostwu.txt ghostwu 20 man

如果是第一行，就输出, print 后面默认为$0( 当前行 ), 如果$0没有写

ghostwu@dev:~/linux/awk$ awk '{ if(NR == 1){ print $1, $2}}' ghostwu.txt ghostwu 20ghostwu@dev:~/linux/awk$ awk '{ if(NR == 1){ print $1; print $2}}' ghostwu.txt ghostwu20

3，利用if....else判断账户是普通用户还是系统用户

ghostwu@dev:~/linux/awk$ awk -v FS=":" '{ if ( $3 < 1000 ){ print $1,"是系统用户"} else { print $1,"是普通用户" } }' /etc/passwdroot 是系统用户ghostwu 是普通用户...

 4，if ... else... if嵌套

ghostwu@dev:~$ awk '{ if( $2 > 0 ) { print "正数" } else if ( $2 == 0 ) { print "0" } else { print "负数" } }' num.txt 正数负数0ghostwu@dev:~$ cat num.txt 1        102       -103       0

5，循环

ghostwu@dev:~$ awk 'BEGIN{ for( i = 1; i <= 6; i++) { print i } }'123456

6，while循环

ghostwu@dev:~$ awk 'BEGIN{ i = 1; do { print "ghostwu",i; i++ } while( i <= 3 )}'ghostwu 1ghostwu 2ghostwu 3ghostwu@dev:~$ awk 'BEGIN{ i = 1; do { print "ghostwu"i; i++ } while( i <= 3 )}'ghostwu1ghostwu2ghostwu3

7，do ... while循环

ghostwu@dev:~$ awk 'BEGIN{ i = 1; do{ print "ghostwu"i; } while( i++ <= 3 ) }'ghostwu1ghostwu2ghostwu3ghostwu4

8，continue

ghostwu@dev:~$ awk 'BEGIN{ for( i = 1; i <= 3; i++ ){ if( i == 2 ){ continue; } print i; } }'13

9，break

ghostwu@dev:~$ awk 'BEGIN{ for( i = 1; i <= 3; i++ ){ if( i == 2 ){ break; } print i; } }'1

10, exit，终止程序执行，如果有END，跳转到END，如果没有，直接退出

ghostwu@dev:~/linux/awk$ awk 'BEGIN{ print "开始"} {print} END{ print "结束" }' ghostwu.txt 开始ghostwu 20 manzhangsan 22lisighostwu 30 manzhanzhao 40 manpeter 20 manzhanzhao 30 man结束ghostwu@dev:~/linux/awk$ awk 'BEGIN{ print "开始";exit} {print} END{ print "结束"" }' ghostwu.txt 开始结束

11，next，让awk直接从下一行开始

ghostwu@dev:~/linux/awk$ awk '{print;next;}' host.txt name    ip地址host1    192.168.1.1host2    192.177.81.1host3    10.0.0.5host4    192.168.3.98host5    192.168.3.98host6    192.168.9.254ghostwu@dev:~/linux/awk$ awk '{if( NR == 1 ){next;} print}' host.txt host1    192.168.1.1host2    192.177.81.1host3    10.0.0.5host4    192.168.3.98host5    192.168.3.98host6    192.168.9.254