AWK's whim - expert articles

1. built-in variables

variable name	description
FS	Input field separator, the default is a space or tab
OFS	Output field separator, the default is a space
RS	Input record separator, default newline \ n
ORS	Output record separator, default newline \ n
NF	Count the number of fields in the current record
NO	No statistical records, each dealing with his record, number will be +1
FNR	No statistical records, each dealing with his record, number will be +1, and NR difference is that, when dealing with the second file, numbered re-count.
ARGC	The number of command line parameters
ARGV	Command line parameter array array sequences, the start index from 0, ARGV [0] is awk
ARGIND	The current file being processed index value. The first file is 1, 2 is the second file, and so on
ABOUT	The current system environment variables
FILENAME	Output current file name processing
IGNORECASE	Ignore case
SUBSEP	Array subscript separator, default is "\ 034"

1.1. FS and OFS

Before the program starts to copy the FS, as with the -F

[root@192 ~]# head -n5 /etc/passwd
root:x:0:0:root:/root:/bin/bash
bin:x:1:1:bin:/bin:/sbin/nologin
daemon:x:2:2:daemon:/sbin:/sbin/nologin
adm:x:3:4:adm:/var/adm:/sbin/nologin
lp:x:4:7:lp:/var/spool/lpd:/sbin/nologin
[root@192 ~]#
[root@192 ~]# head -n5 /etc/passwd|awk 'BEGIN{FS=":"}{print $1,$2}'
root x
bin x
daemon x
adm x
lp x
OFS由于默认是空格，输出如果是：,那么逗号会变为*
[root@192 ~]# head -n5 /etc/passwd|awk 'BEGIN{FS=":";OFS="*"}{print $1,$2}'
root*x
bin*x
daemon*x
adm*x
lp*x

1.2. RS and ORS

RS默认\n，指定分割符 ,ORS默认换行符，也可以指定输出符号
也就是说 将分割符换成你想要的样子

[root@192 ~]# tail -n2  /etc/services |awk 'BEGIN{RS="/";ORS="+"}{print $0}'
iqobject        48619+udp               # iqobject
matahari        49000+tcp               # Matahari Broker

1.3. NF

字段统计
[root@192 ~]# tail -n2 /etc/services |awk 'BEGIN{FS="/"}{print $NF}'
tcp               # 3GPP Cell Broadcast Service Protocol
tcp               # Image Systems Network Services

[root@192 ~]# tail -n 2 /etc/services |awk 'BEGIN{FS="/"}{print NF}'
2
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