awk: Program Elements(5)

1. Command-line Arguments
awkCommand:

 BEGIN {  
   print ARGC;  
   for (k=0; k < ARGC; k++)  
   {  
     print "ARGV[" k "]=" ARGV[k];  
   }  
 }  
   
 {  
   print $0;  
 }  

awkCommand2:

 BEGIN{  
   print ARGC;  
   for(k=0; k<ARGC; k++)  
   {  
     print "ARGV[" k "]=" ARGV[k];  
   }  
 }     

text:

 Hello world!!  
 Amazing world!  

./script_1:

 #! /bin/bash  
   
 #Following is error statement, it will take the program  
 #as input file, and complain no such a file  
 echo "" | awk -v var1=1 -v var2=2 Hello world! var3=3 '{  
   print ARGC;  
   for (k=0; k < ARGC; k++)  
   {  
     print "ARGV[" k "]=" ARGV[k];  
   }  
 }'   
   
 #Following is also error statement, it will take Hello as the   
 #input file, and complain no such a file.  
 #Actually awk can take input from 2 sources, either standard   
 #input(pipe) or input files. If providing the input files, awk  
 #will ignore the input from pipe/starndard input.  
 #In this case, "Hello" "world!" and "var3=3" are taken as   
 #3 input files.   
 echo "" | awk -v var1=1 -v var2=2 '{  
   print ARGC;  
   for (k=0; k < ARGC; k++)  
   {  
     print "ARGV[" k "]=" ARGV[k];  
   }  
 }' Hello world! var3=3  
   
 #awk ignore the input from pipe, and choose the input  
 #from text file.  
 echo "Amazing New York" | awk '{  
   print $0;  
 }' text  
 #output:   
 #Hello world!!  
 #Amazing world!  
   
 #Following statement successfully read into the 3 options, but  
 #still take "Hello" as the input file name and complain no such  
 #a file.  
 echo "" | awk -v var1=1 -v var2=2 -f awkCommand Hello world! var3=3  
 #output:  
 #4  
 #ARGV[0]=awk  
 #ARGV[1]=Hello  
 #ARGV[2]=world!  
 #ARGV[3]=var3=3  
 #awk: cannot open Hello (No such file or directory)  
   
 #Following statement successfully read into the option, and   
 #successfully get the text's information  
 awk -v var1=1 -v var2=2 -f awkCommand text  
 #output:  
 #2  
 #ARGV[0]=awk  
 #ARGV[1]=text  
 #Hello world!!  
 #Amazing world!  
   
 #since awkCommand2 only has "BEGIN" action, and not  
 #having any "pattern/action" pair. In this case,   
 #"Hello", "world" will be taken as pure arguments,  
 #instead of input source file  
 awk -f awkCommand2 Hello world  
 #output:  
 #3  
 #ARGV[0]=awk  
 #ARGV[1]=Hello  
 #ARGV[2]=world  

2. Environment Variables
When launching the awk script, awk will inherit the environment variable.

 #! /bin/bash  
   
 awk 'BEGIN {  
   print ENVIRON["HOME"];  
   print ENVIRON["USER"];  
   #output:  
   #/home/aubinxia  
   #aubinxia  
 }'