awk: User Controlled Input(2)

1. User Controlled Input: from terminal:
text:

 Hello world!  
 Hello Amazing world!  

script_1:

 #! /bin/bash  
   
 awk 'BEGIN {  
   getline < "/dev/tty";  
 #script stops here, waiting for input:  
 #Input:  
 #My Input  
   
   print "BEGIN:" $0;  
   print "BEGIN, NF, NR:",NF,NR;  
 #Output:  
 #My Input  
 #BEGIN:My Input  
 #BEGIN, NF, NR: 2 0  
   
   getline v < "/dev/tty";  
 #Input:  
 #My Own Input  
 #Since getline read input into variable v, instead of $0,  
 #so, NF is not touched.  
   
   print "BEGIN:" v;  
   print "BEGIN, NF, NR:", NF, NR;  
 #Output:  
 #My Own Input  
 #BEGIN:My Own Input  
 #BEGIN, NF, NR: 2 0  
 }  
 { print $0; }' text  

terminal:

 aubinxia@aubinxia-fastdev:~/Desktop/xxdev$ ./script_1  
 My Input  
 BEGIN:My Input  
 BEGIN, NF, NR: 2 0  
 My Own Input  
 BEGIN:My Own Input  
 BEGIN, NF, NR: 2 0  
 Hello world!  
 Hello Amazing world!  

2. User Controlled Input: while loop
text:

 Hello world!  
 Hello Amazing world!  

text2:

 Hello Chicago  
 Hello Los Angeles  
 Hello Boston  
 Hello Atlantic  

script_1:

 #! /bin/bash  
   
 awk 'BEGIN {  
   # getline returning 1 means "success"  
   # returning 0 means "end of file"  
   # returning -1 means error  
   while( getline < "text2" )  
   {  
     print "BEGIN:" $0;  
   }  
 }  
 { print $0; }' text  

terminal:

 aubinxia@aubinxia-fastdev:~/Desktop/xxdev$ ./script_1  
 BEGIN:Hello Chicago  
 BEGIN:Hello Los Angeles  
 BEGIN:Hello Boston  
 BEGIN:Hello Atlantic  
 Hello world!  
 Hello Amazing world!  

3. User Controlled Input: from external command
text2:

 Hello Chicago  
 Hello Los Angeles  
 Hello Boston  
 Hello Atlantic  

script_1:

 #! /bin/bash  
   
 awk 'BEGIN {  
   command="cat text2";  
   # Sice we do not close the command every time after  
   # "getline", so for each iteration, getline will  
   # read the next record compared to the one in the  
   # last iteration.  
   while((command | getline v)>0)  
     print v;  
   close(command);  
 }'  

terminal:

 aubinxia@aubinxia-fastdev:~/Desktop/xxdev$ ./script_1  
 Hello Chicago  
 Hello Los Angeles  
 Hello Boston  
 Hello Atlantic