how to skip specific lines in awk and print the remaining - awk

Question

how can I read only lines: 3,9,12, 15 from the file containing the ff lines.
The idea is whenever I get x and y , I wanted to print the last line among lines containing x and y.
What I meant is , for example , if I have awk script like : BEGIN { name = $2; value=$3; } { if(name == x && value==y && the scan reaches at lines 3, 9, 12 and 15) printf("hello world") }. what expression can I use instead of "the scan reaches at lines 3, 9 12 and 15"
1 x y
2 x y
3 x y
4 a d
5 e f
6 x y
7 x y
8 x y
9 x y
10 g f
11 x y
12 x y
13 p r
14 w c
15 x y
16 a z

Answer 1

One way with awk:
$ awk '/^[0-9]+ x y$/{a=$0;f=1;next}f{print a;f=0}' file
3 x y
9 x y
12 x y
15 x y
One way without awk:
$ tac file | uniq -f1 | fgrep -w 'x y' | tac
3 x y
9 x y
12 x y
15 x y

Answer 2

Some like this?
awk 'a=="xy" && $2$3!="xy" {print b} {a=$2$3;b=$0}' file
3 x y
9 x y
12 x y
15 x y

Answer 3

You need to use two while loops here one to check the line and another to iterate. Something like this. Hope that helps
String line = "";
int i = 0;
try {
BufferedReader in = new BufferedReader(new FileReader("D:\\readline.txt"));
while ((line = in.readLine()) != null) {
i++;
if (line.charAt(0) == 'x' && line.charAt(2) == 'y') {
System.out.println("Line containg Y and Y");
String searchline = line;
while ((line = in.readLine()) != null) { //Iterate untill you find the last line of X and Y
i++; //To keep count of the line read
if (line.charAt(0) == 'x' && line.charAt(2) == 'y') {
searchline = line;
continue;
} else {
break;
}
}
System.out.println("Printing the line ::" + (i - 1) + ":: containing X and Y::::::::" + searchline);
}
}
} catch (Exception e) {
System.out.println("Exception Caught::::");
}
}