文本编辑的一点心得--awk篇

zw421961

厉害，awk大神。。:wink:

xxf19872

学习了 。。。。。。。。。。。。。。。。。。。。。。

zw421961

好厉害啊，总结的很好

lxzkenney

回复 5# justlooks


    打印偶数行
awk 'i++%2'

这个没看懂！
大神有时间解释一下。

seq 10|awk 'i++%2'
2
4
6
8
10
-------------------------------
i初始是空。i++后是1. 1%2 余1,1是真，应该打印1才对啊。
2%2是0。不应该打印2啊。

haokoo

回复 105# lxzkenney


    i++%2  -->  先得出结果0，i再自加；如果++i%2 ，i先自加再进行%的运算

seq 10 | awk ' i++%2'  得偶数
seq 10 | awk ' ++i%2'  得奇数

莫侠007

ly5066113@ubuntu:~$ cat urfile
1
a

2
a


3
ly5066113@ubuntu:~$ awk -v RS="" '{print "#" $0 "#"}' urfile
#1
a#
#2
a#
#3#
ly5066113@ubuntu:~$ awk -F "b" -v RS="" '{print $1}' urfile
1
2
3

[root@gateway-182 ~]# awk -F "d" -v RS="" '{print $1,$2}' urfile
1 a
2 a
3

[root@gateway-182 ~]# awk -F "c" -v RS="" '{print $2}' urfile   
a
a

[root@gateway-182 ~]# awk -F "a" -v RS="" '{print $1,$2}' urfile  
1
2
3

这里有点不明白，这里不是指定c为列的分隔符了么，为什么$2=a呢

cjxulicong

好东西哈.最近在研究awk。mark一个.

gxyyq

，要好好看，要仔仔细细的去看，努力学会！

jeffreyst

mark，学习下

expert1

回复 1# ly5066113


    多谢tim的大作，不过根据官方手册，有个地方要改一下，

{code}

如果RS被设置为空，那么awk会将连续的空行作为行分隔符，与RS设置成"\n\n+"有什么区别？？？
1、忽略文件开头和结尾的空行。且文件不以记录分隔符结束，即最后不是空行，会将最后一个记录的尾\n去掉
2、不设置RT变量（测试未发现规律，暂时认为RT变量不可用）

{/code}

RT不可用，严格说应该是匹配为空。

这是官方手册

The following table summarizes how records are split, based on the value of RS:

RS == "\n"
Records are separated by the newline character (‘\n’). In effect, every line in the data file is a separate record, including blank lines. This is the default.

RS == any single character
Records are separated by each occurrence of the character. Multiple successive occurrences delimit empty records.

RS == ""
Records are separated by runs of blank lines. When FS is a single character, then the newline character always serves as a field separator, in addition to whatever value FS may have. Leading and trailing newlines in a file are ignored.

RS == regexp
Records are separated by occurrences of characters that match regexp. Leading and trailing matches of regexp delimit empty records. (This is a gawk extension; it is not specified by the POSIX standard.)

In all cases, gawk sets RT to the input text that matched the value specified by RS. But if the input file ended without any text that matches RS, then gawk sets RT to the null string.