siwen

# if
if(expression)
	statement
	
# if-else
if(expression)
	statement1
else
	statement2 
	
# if-else-if
if(expression)
	statement1 
else if (expression2)
	statement2 
else
	statement3 

# while loop
while(expression){
	statement
}

# for loop
# Format 1
for(initial variable; loop condition; loop increment/decrement statement){
	statement
}

# Format 2 
for(variable in array){
	statement
}

# do-while loop
do{
	statement
} while(condition)

[root@localhost ~]# awk 'BEGIN{str="a,b,c,d";len=split(str,arr,",");print len,length(arr),asort(arr),arr[1]}'
4 4 4 a

# Method 1
[root@localhost ~]# awk 'BEGIN{
str="a,b,c,d";
len=split(str,arr,",");
for(i in arr){
print i,arr[i];
}
}'
1 a
2 b
3 c
4 d

# Method 2 (awk arrays are associative arrays, this method ensures ordered traversal)
[root@localhost ~]# awk 'BEGIN{
str="a,b,c,d";
len=split(str,arr,",");
for(i=1;i<=len;i++){
print i,arr[i];
}
}'
1 a
2 b
3 c
4 d

# Check if the array contains a certain key
if(key in arr)

# Check if arr is an array
isarray(arr)  If arr is an array, returns 1, otherwise returns 0.
typeof(arr)   Returns the data type; if arr is an array, returns 'array'.

# For a 3*3 two-dimensional array arr:
1 2 3 
4 5 6
7 8 9
In C language, arr[0][0] = 100; in awk, we can set arr[0,0] = 100, and so on: arr[0,1], arr[0,2]...arr[3,3];
In fact, 0,1   0,2   3,3   are just string indexes.

# Get a random integer between 0-99
[root@localhost ~]# awk 'BEGIN{srand();randint=int(100*rand());print randint}'

# asort(arr[,d])  arr-->array d-->array; if this parameter is passed, it will not modify arr, but will copy all elements from arr to d, and then sort d
[root@localhost ~]# awk 'BEGIN{
    arr[11]=800;
    arr[22]=200;
    arr[33]=300;
    arr[44]=100;
	for(i in arr){
        print i,arr[i];
    }
    asort(arr);
    print;
    for(j in arr){
        print j,arr[j];
    }
}'
11 800
22 200
33 300
44 100

1 100
2 200
3 300
4 800

# asorti
[root@localhost ~]# awk 'BEGIN{
	arr[11]=800;
	arr[22]=200;
	arr[33]=300;
	arr[44]=100;
    for(i in arr){
        print i,arr[i];
    }
    asorti(arr);
    print;
    for(j in arr){
        print j,arr[j];
    }
}'
11 800
22 200
33 300
44 100

1 11
2 22
3 33
4 44

# gsub(regexp, sub, str)
[root@localhost ~]# awk 'BEGIN{
    str="hello world";
    gsub("[o|l]","*",str);
    print str;
}'
he*** w*r*d

# sub(search, sub, str)
[root@localhost ~]# awk 'BEGIN{
    str="hello world";
    sub("[o|l]","*",str);
    print str;
}'
he*lo world

# index(str, sub)
[root@localhost ~]# awk 'BEGIN{
    str="hello world";
    idx=index(str,"l");
    print idx;
}'
3

# match(str, regexp)
[root@localhost ~]# awk 'BEGIN{
    str="hello world hi haaaaaa";
    idx=match(str,"h*");
    print idx;
}'
1

# strtonum(str)
[root@localhost ~]# awk 'BEGIN{
    str="01010";
    res=strtonum(str);
    print res;
}'
520

# substr(str, start, len)
[root@localhost ~]# awk 'BEGIN{
    str="hello world";
    res=substr(str,7,5);
    print res;
}'
world

# tolower(str)
[root@localhost ~]#  awk 'BEGIN{
    str="HAHAHA";
    res=tolower(str);
    print res;
}'
hahaha

# toupper(str)
[root@localhost ~]# awk 'BEGIN{
    str="hello world";
    res=toupper(str);
    print res;
}'
HELLO WORLD

# systime()
[root@localhost ~]# awk 'BEGIN{print systime()}'
1672448348

# mktime(datespec)
[root@localhost ~]# awk 'BEGIN{print mktime("2022 12 31 09 00 00")}'
1672448400

# strftime([format [, timestamp]])
[root@localhost ~]# awk 'BEGIN{print strftime("%c",systime())}'
Sat Dec 31 09:03:53 2022

# close(expr) 
[root@localhost ~]# awk 'BEGIN{while("cat emp.txt" | getline){print $0}close("emp.txt")}'

# system(command)
[root@localhost ~]# awk 'BEGIN{system("ls -l")}'

# getline
[root@localhost ~]# awk '{getline;print}' emp.txt
002 Li Si 2000 10
004 Zhao Liu 2000 20
006 Xiao Li 800 20

[root@localhost ~]# awk 'BEGIN{print "Input:";getline name;print name}'
Input:
123
123

# next
[root@localhost ~]# awk '{if($3<2000)next;print}' emp.txt
002 Li Si 2000 10
003 Wang Wu 3000 10
004 Zhao Liu 2000 20

# nextfile
[root@localhost ~]# awk '{if($3==2000) nextfile;print}' emp.txt file
001 Zhang San 1000 10
xxx is a hanhan. ^_^

are you kidding?
I think ...
My phone number is 1872272****.

function function_name(parameter1, parameter2, ...) { 
   function body
}

# Call a function without parameters
fun_name 
# Call a function with parameters
fun_name(arg1[,arg2...])
# Call a function with return value
var = fun_name([arg1...])

# Function without parameters
[root@localhost ~]# awk 'BEGIN{
	fun1()
}
function fun1(){
	print "this is a function!"
}'
this is a function!

# Function with parameters
[root@localhost ~]# awk 'BEGIN{
	fun2(10,20)
}
function fun2(num1,num2){
	print "The result of the function is:"num1+num2
}'
The result of the function is:30

# Function with return value
[root@localhost ~]# awk 'BEGIN{
	res = fun3(10,20);
	print "The sum of num1 and num2 is:"res
}
function fun3(num1,num2){
	return num1+num2
}'
The sum of num1 and num2 is:30