How does Awk's pattern matching for strings works? - awk

Question

I am trying to understand how the range pattern matching work in Awk
Here is the full data that I am practicing with
Raw Data
-----------------------------------------
USSR 8649 275 Asia
Canada 3852 25 North America
China 3705 1032 Asia
USA 3615 237 North America
Brazil 3286 134 South America
India 1267 746 Asia
Mexico 762 78 North America
France 211 55 Europe
Japan 144 120 Asia
Germany 96 61 Europe
England 94 56 Europe
If I write this code
$ awk '/Asia/, /Europe/' countries.awk
I get
USSR 8649 275 Asia
Canada 3852 25 North America
China 3705 1032 Asia
USA 3615 237 North America
Brazil 3286 134 South America
India 1267 746 Asia
Mexico 762 78 North America
France 211 55 Europe
Japan 144 120 Asia
Germany 96 61 Europe
It doesn't output England.
And If I write this
$ awk '/Europe/, /Asia/' countries.awk
I get
France 211 55 Europe
Japan 144 120 Asia
Germany 96 61 Europe
England 94 56 Europe
What is the behavior here? Why do I not get England on the first one?

Answer 1

Awk process input lines one at a time, the syntax you used is likely to print lines from the start to the end pattern, represented by country names. When you used
awk '/Asia/, /Europe/'
The start of pattern Asia happens more than once. As you can see from the line numbers below, numbers 3,5,8 and 11 represent the start of the pattern and the pattern ends at lines 10 and 12. Observe carefully the sub-ranges of lines between 8-10 and 11-12. The last end pattern Europe for the last Asia ends at line 12, that is the reason you are not seeing England in the first case.
But when you used
awk '/Europe/, /Asia/'
The line containing the first start pattern Europe starts at line 10 and ends at 11 another two pattern start at 12 and 13 without an end pattern Asia, so it would obviously print all the lines until Asia appears. So you are seeing England in the second case.
$ cat -n file
1 Raw Data
2 -----------------------------------------
3 USSR 8649 275 Asia
4 Canada 3852 25 North America
5 China 3705 1032 Asia
6 USA 3615 237 North America
7 Brazil 3286 134 South America
8 India 1267 746 Asia
9 Mexico 762 78 North America
10 France 211 55 Europe
11 Japan 144 120 Asia
12 Germany 96 61 Europe
13 England 94 56 Europe

Answer 2

Never use range expressions as they make trivial tasks very slightly briefer but then need a complete rewrite or duplicate conditions when your requirements change. Always use a flag instead:
awk '/Asia/{f=1} f{print} /Europe/{f=0}' countries.awk
I bet if you started with that you wouldn't even have had to ask this question as the logic is clear and explicit.