Awk from getting started to digging in (4) user defined variables

No type

BEGIN{}{    num = 100;      #  Save an integer first      print("num is: "num);    num = 3.1415926; #  Save another floating point number     print("num is: "num);    num = "I'm string."; #  Finally, look at the string     print("num is:"num);}END{}

$echo “” |awk -f chapter_2_2-1.awk
num is: 100
num is: 3.14159
num is:I’m string.

awk Variables, like all other scripting languages, are untyped , You can store any type of value , And can be changed at any time , The latter is different from languages that support type inference （ Such as ：C#, Although there is no need to specify the type when defining , But once assigned, the type is fixed ）.

There is no need to define

BEGIN{}{    print("var is:"var); #  I wipe it up. , This is directly used }END{}

$echo “”|awk -f chapter_2_2-2.awk
var is:

Variable write as you use , Even if you use uninitialized variables, there will be no error .

Overall

BEGIN{    print("i in begin: "i);}{    ++i;    print("i in body: "i);}END{    print("i in end: "i);}

$cat chapter_2_2-3.awk |awk -f chapter_2_2-3.awk
i in begin:
i in body: 1
i in body: 2
i in body: 3
i in body: 4
i in body: 5
i in body: 6
i in body: 7
i in body: 8
i in body: 9
i in body: 10
i in end: 10

awk All variables in , Whether it is in BEGIN Medium 、BODY Medium 、END Medium , Or what will be mentioned later function Medium , It's all about the overall situation , That is, as long as the variable name is the same , No matter where it is modified , Its value will continue to the next executed code line . This is what we should pay special attention to when using variables , Otherwise, it may cause all kinds of inexplicable problems .

Transfer parameter variable

BEGIN{    print(x);    print("i in begin: "i);}{    ++i;    print("i in body: "i);}END{    print("i in end: "i);}

$cat chapter_2_2-4.awk |awk -v x=“I’m X” -v i=100 -f chapter_2_2-4.awk
I’m X
i in begin: 100
i in body: 101
i in body: 102
i in body: 103
i in body: 104
i in body: 105
i in body: 106
i in body: 107
i in body: 108
i in body: 109
i in body: 110
i in body: 111
i in end: 111

Variables can be assigned in the program or called on the command line , As the above routine ,x and i The values of are all passed in as command line parameters , This way of parameter passing expands the applicability of scripting .