BEGIN和END关键字是来用来读取数据流之前或之后执行命令的特殊模式
1、内建变量
FIELDWIDTHS：由空格分隔开的的定义每个数据字段确切宽度的一列数字
FS：输入字段分隔符
RS：输入数据行分隔符
OFS：输出字段分隔符
ORS：输出数据行分隔符
[[email protected] conf]# cat data2 data1,data2,data3,data4,data5 data6,data7,data8,data9,data10 data11,data12,data13,data14,data15
[[email protected] conf]# gawk ‘BEGIN{FS=",";OFS="-"} {print $1,$2,$3}‘ data2
data1-data2-data3
data6-data7-data8
data11-data12-data13
数据流占多行情况下
把RS变量设置成空白字符串，然后在数据行间留一个空白行。gawk会把每个空白行当作一个数据行分隔符
[[email protected] conf]# cat data3 Tom Mullen 123 Main Street Chicago.IL 6001 (312)555-1234 Frank Williams 456 Oak street Indianpolis.IN 46201 (317)55-9786
[[email protected] conf]# gawk ‘BEGIN{FS="\n";RS=""} {print $1,$4}‘ data3
Tom Mullen (312)555-1234
Frank Williams (317)55-9786
2、数据变量
FNR：当前数据文件中的数据行数
NF：数据文件中的字段总数
NR：已处理的输入数据行数目
[[email protected] conf]# gawk ‘BEGIN{FS=":";OFS=";"}{print $1,$NF}‘ /etc/passwd
root;/bin/bash
bin;/sbin/nologin
daemon;/sbin/nologin
adm;/sbin/nologin
lp;/sbin/nologin
[[email protected] conf]# cat data2
data1,data2,data3,data4,data5
data6,data7,data8,data9,data10
data11,data12,data13,data14,data15
[[email protected] conf]# gawk ‘
BEGIN{FS=","}
{print $1,"FNR="FNR,"NR="NR}
END{print "there were",NR,"records processed"}‘ data2 data2
data1 FNR=1 NR=1
data6 FNR=2 NR=2
data11 FNR=3 NR=3
data1 FNR=1 NR=4
data6 FNR=2 NR=5
data11 FNR=3 NR=6
there were 6 records processed
3、自定义变量
变量名不能以数字开头，
[[email protected] conf]# gawk ‘
> BEGIN{
> testing="this is a test"
> print testing
> }‘
this is a test
[[email protected] conf]# gawk ‘BEGIN{X=4;X=X*2+3;print X}‘
11
在命令行上给变量赋值
[[email protected] tmp]# cat script1
#!/bin/bash
#
BEGIN{FS=","}
{print $n}
[[email protected] tmp]# cat data3
data1,data2,data3,data4,data5
data6,data7,data8,data9,data10
data11,data12,data13,data14,data15
[[email protected] tmp]# gawk -f script1 n=2 data3
data2
data7
data12
在设置变量后，这个值在代码的BEGINU部分不可用
[[email protected] tmp]# vim script1
#!/bin/bash
#
BEGIN{print "the starting value is ",n;FS=","}
{print $n}
[[email protected] tmp]# gawk -f script1 n=3 data3 the starting value is data3 data8 data13
加上-v，允许你指定BEGIN代码部分之前设定的变量
[[email protected] tmp]# gawk -f script1 -v n=3 data3 the starting value is 3 data3 data8 data13
4、遍历数组
for (var in array)
{
statements
}
for语句在每次将关联数组array的下一个索引值赋给变量var时，执行一遍statements。
记住这个变量是索引值而不是数组元素的值
[[email protected] tmp]# gawk ‘BEGIN{
var["a"]=1
var["g"]=2
var["m"]=3
var["u"]=4
for (test in var)
{
print "Index:",test," - Valuse:",var[test]
}
}‘
Index: u - Valuse: 4
Index: m - Valuse: 3
Index: a - Valuse: 1
Index: g - Valuse: 2
删除数组的变量
从关联数组中删除数组索引要用一个特别命令
delete array[index]
[[email protected] tmp]# gawk ‘BEGIN{
var["a"]=1
var["g"]=2
for (test in var)
{
print "Index:",test,"- Value",var[test]
}
delete var["g"]
print "------------"
for (test in var)
{
print "Index:",test,"- Value",var[test]
}
> }‘
Index: a - Value 1
Index: g - Value 2
------------
Index: a - Value 1
5、匹配操作符
匹配操作符(~)，允许将正则表达式限定在数据行中的特定数据字段。
$1 ~/expression/
用正则表达式/^data2/来匹配第二个数据段，过滤第二个字段以文本data2为开头的行
[[email protected] tmp]# cat data3
data1,data2,data3,data4,data5
data6,data7,data8,data9,data10
data11,data12,data13,data14,data15
data21,data22,data23,data24,data25
[[email protected] tmp]# gawk ‘BEGIN{FS=","} $2 ~/[^data2]/{print $0}‘ data3
data6,data7,data8,data9,data10
data11,data12,data13,data14,data15
gawk程序脚本常用在数据文件查找特定数据元素的强大工具
[[email protected] tmp]# gawk -F: ‘$1 ~/root/{print $1,$NF}‘ /etc/passwd
root /bin/bash
用!符号来排除正则表达式的匹配
$1 !~/expression/
gawk -F: ‘$1 !~/root/{print $1,$NF}‘ /etc/passwd
6、数学表达式
x == y
x <= y
x < y
x >= y
x > y
如显示所有属于root用户组的（组ID为0）的系统用户
[[email protected] tmp]# gawk -F: ‘$4==0{print $1}‘ /etc/passwd
root
sync
shutdown
halt
operator
对文本数据使用表达式，必须要小心，跟正则表达式不同，表达式必须完全匹配
[[email protected] tmp]# gawk -F, ‘$1== "data1" {print $1}‘ data3
data1
6、if语句
if (condition)
statement1
或者 if (condition) statement1
[[email protected] tmp]# cat data4
10
5
3
13
55
[[email protected] tmp]# gawk ‘{if ($1>20) print $1}‘ data4
55
[[email protected] tmp]# gawk ‘{
> if ($1>20)
> {
> x=$1 * 2
> print x
> }
> }‘ data4
110
gawk的if语句也支持else子句，允许在if语句条件不成立的情况下执行一条或多条语句。
[[email protected] tmp]# gawk ‘{
> if ($1>100)
> {
> x=$1 * 2
> print x
> } else
> {
> x=$1 / 2
> print x
> }}‘ data4
5
2.5
1.5
6.5
27.5
也可以这么写
if (condition) statement1:else statement2
[[email protected] tmp]# gawk ‘{if ($1>100) print $1*2;else print $1/2}‘ data4
5
2.5
1.5
6.5
27.5
7、while语句
while (condition)
{
statement1
}
[[email protected] tmp]# cat data5
120 130 135
160 113 140
145 170 215
[[email protected] tmp]# gawk ‘{
total=0
i=1
while (i<4)
{ total+=$i
i++
}
avg=total/3
print "Averaget:",avg
}‘ data5
Averaget: 128.333
Averaget: 137.667
Averaget: 176.667
Averaget: 0
8、do-while语句
do
{
statement1
} while (condition)
[[email protected] tmp]# gawk ‘{
total=0
i=1
do
{
total+=$i
i++
}while (total<150)
print total}‘ data5
250
160
315
9、for语句
for (variable assignment;condition;interation process)
[[email protected] tmp]# gawk ‘{
> tatal=0
> for (i=1;i<4;i++)
> {
> total+=$i
> }
> avg=total/3
> print "Average:",avg
> }‘ data5
Average: 128.333
Average: 266
Average: 442.667
Average: 442.667
[[email protected] tmp]# gawk ‘{for (i=1;i<4;i++) total+=$i;avg=total/3;print "Average:",avg}‘ data5
Average: 128.333
Average: 266
Average: 442.667
Average: 442.667
[[email protected] tmp]# cat data5
120 130 135
160 113 140
145 170 215
10、格式化打印
在printf命令末尾手动添加换行符来生成新行
如果需要几个单独的printf命令来在同一行上打印多个输出
[[email protected] tmp]# cat data3
data1,data2,data3,data4,data5
data6,data7,data8,data9,data10
data11,data12,data13,data14,data15
data21,data22,data23,data24,data25
[[email protected] tmp]# gawk ‘BEGIN{FS=","}{printf "%s ",$1}END{printf "\n"}‘ data3
data1 data6 data11 data21
[[email protected] tmp]# gawk ‘BEGIN{FS=","}{printf "%s ",$1}‘ data3
data1 data6 data11 data21 [[email protected] tmp]#
时间： 2024-11-03 05:32:15