Shell Programming and Scripting

I am beginner in awk

awk 'BEGIN{for(i=1;(getline<"opnoise")>0;i++) arr[i]=$1}{print arr[20]}'

In the above script, opnoise is a file, I am reading it into an array and then printing the value corresponding to index 20. Well this is not my real objective, but I have posted this example to describe the problem.

The problem is when I execute the script there is no activity(no error, just a blank) and the body i.e, the print statement, execute only when I hit "ENTER" for the second time. Also gawk does not exit to command prompt automatically, I have to hit CTRL+C to exit and awk gets displayed while exiting.

Here is what happens,

user@server ~/folder
$ awk 'BEGIN{for(i=1;(getline<"opnoise")>0;i++) arr[i]=$1}{print arr[20]}'

684
awk

user@server ~/folder
$

Code:

awk '{a[FNR]=$1} END{print a[20]}' opnoise
OR (better yet)
awk 'FNR==20 {print $1;exit}' opnoise

hmmm if you want to print the 20th element
this will do..

Code:

awk '{A[NR]]=$1}END{print A[20]}' opnoise

and in you awk the print statement is outside the BEGIN block

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Actually this what I am trying to do. I need to use the values in the array to remove certain records in file opwflightno and make a new file opwonoise. But awk is not executing beyond BEGIN. I had posted a simple example to describe the problem.



awk 'BEGIN {for(i=1;(getline < “opnoise”)>0; i++) arr[i]=$1}{for(j=1; j<=i; j++){if(arr[j]!=$1){print $0}}}' opwflightno > opwonoise

Code:

nawk '
  FNR==NR {arr[FNR]=$1;next}
  $1 == arr[FNR]
' opnoise opwflightno > opwonoise

I am getting command not found. All I did was replace nawk with gawk. I do not have nawk.