Shell Programming and Scripting

sorry about the curlies - here's a newER version with comments:

Code:

awk '
   # dealing with the FIRST specified file - opnoise 
   # for every line/record in the FIRST file, create an array (arr) indexed by FNR
   # with the value of the first field ($1)
   # go to the next record/line (next)
   FNR==NR {arr[FNR]=$1; next} 

   # Here we're dealing with the SECOND file specified on the command line - (opwflightno)
   # if the array (arr) cell indexed by FNR equal the value of the first field ($1) - 
   # print the entire record/line.
   $1==arr[FNR]
' opnoise opwflightno > opwono

I am beginner, and would like to know the following

* Does the command read the files one by one, or does it read it simultaneously?

* How does it know which command is for which file?

* How does this command work without any curlies, if statement or print statement.

* In my case opnoise has 1000 unique records(2, 7, 12 and so on ) with just one field, where as opwflightno has 4560500 records with repetitive first field, and other fields of course. For example, it has 5000 records with first field value 2, 3000 records with first field value 3, 1200 records with first field 7 and so on.

*How do I get all the records from opwflightno that do not have first field equal to the first field of opnoise? In reference to the above example I would want all the records with first field equal to 3 and disregard the ones with first field 2 and 7.

one by one
As the comments outlined, the condition 'FNR==NR' is true only when reading the FIRST file
which command? ' '$1 == arr[FNR]'? If the condition is true and there's no
associated 'action', the default action is 'print $0'.
What is the question?

Code:

awk 'FNR==NR {f1[$1];next} !($1 in f1)' opnoise opwflightno > opwono

Thanks a lot! I really appreciate your help

---------- Post updated at 05:47 PM ---------- Previous update was at 05:23 PM ----------

What values are assigned to array f[$1]? I understand its indexed by $1 of file opnoise. Or I guess the index does not matter in this case, its just creates an array with all the records in $1 of file opnoise. Am I thinking right? Could you please further explain the meaning of f1[$1].

'f1[$1]' - creates a 'cell' in array 'f1' indexed' by '$1' with no associated value - "we ain't need no st*ing values" in this case.

Clear! Thanks a lot