awk应用

awk应用

一. awk使用

1. 例

文件有多少行，取决于文件有多少行

1.
[root@node6 ~]# cat abc 
this line of data is ignored.
[root@node6 ~]# awk '{print "hello hello"}' abc 
hello hello
[root@node6 ~]# echo '' >> abc 
[root@node6 ~]# cat abc 
this line of data is ignored.

[root@node6 ~]# 
[root@node6 ~]# awk '{print "hello hello"}' abc 
hello hello
hello hello

2.begin 开始
[root@node6 ~]# awk '{print "abc"}'

abc

abc
^C
[root@node6 ~]# awk 'BEGIN{print "abc"}'
abc
[root@node6 ~]# 


3.
[root@node6 ~]# cat abc 
this line of data is ignored.

[root@node6 ~]# awk '/^$/{print "This is a blank line"}' abc 
This is a blank line
[root@node6 ~]# echo "" >> abc 
[root@node6 ~]# cat abc 
this line of data is ignored.


[root@node6 ~]# awk '/^$/{print "This is a blank line"}' abc 
This is a blank line
This is a blank line
[root@node6 ~]# 
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2. 例

[root@node6 ~]# cat abc 
1 2 3 
a b c

1
a A B C 
2

[root@node6 ~]# awk '/[0-9]+/{print "That is an integer"}' abc //查看数字，0到正无穷，0,1,2...任意一次
That is an integer
That is an integer
That is an integer
[root@node6 ~]# awk '/[A-Za-z]+/{print "That is a string"}' abc //查看字母
That is a string
That is a string
[root@node6 ~]# awk '/^$/{print "That is a blank line"}' abc //空行
That is a blank line
That is a blank line
[root@node6 ~]# 
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3. 例

开始 正文 结束

在begin定义的变量，后面可以使用
[root@node6 ~]# echo "a b c d"|awk 'BEGIN{one=1;two=2}{print $(one + two)}'
c
[root@node6 ~]# 


[root@node6 ~]# echo "a b c d"|awk 'BEGIN{one=1;two=2}{print $(one + two)}END{print "1 + 2 = "(1+2)}'
c
1 + 2 = 3
[root@node6 ~]# 
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4. 字段和引用的分离

awk 允许使用字段操作符$来指定字段。在该操作符后面跟着一个数字或变量，用于标识字段的位置。”$1”表示第一个字段，$2表示第二个字段等等。$O”表示整个输入记录。下面的例子显示了第一个字段是姓，第二个字段是名字，后面是电话号码。


[root@node6 ~]# cat abc 
john robinson 666-555-1111
[root@node6 ~]# awk '{print $2,$1,$3}' abc 
robinson john 666-555-1111
[root@node6 ~]# 
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