Using pipe and shell command in awk script - awk

Question

I am writing an awk script which needs to produce an output which needs to be sorted.
I am able to get the desired unsorted output in an awk array. I tried the following code to sort the array and it works and I don't know why and whether it is the expected behavior.
Sample Input to the question:
Ram,London,200
Alex,London,500
David,Birmingham,300
Axel,Mumbai,150
John,Seoul,450
Jen,Tokyo,600
Sarah,Tokyo,630
The expected output should be:
Birmingham,300
London,700
Mumbai,150
Seoul,450
Tokyo,1230
The following script is required to show the city name along with the respective cumulative total of the integers present in the third field.
BEGIN{
FS = ","
OFS = ","
}
{
if($2 in arr){
arr[$2]+=$3;
}else{
arr[$2]=$3;
}
}
END{
for(i in arr){
print i,arr[i] | "sort"
}
}
The following code is in question:
for(i in arr){
print i,arr[i] | "sort"
}
The output of the print is piped to sort, which is a bash command.
So, how does this output travel from awk to bash?
Is this the expected behavior or a mere side effect?
Is there a better awk way to do it? Have tried asort and asorti already, but they exist with gawk and not awk.
PS: I am trying to specifically write a .awk file for the task, without using bash commands. Please suggest the same.

Answer 1

Addressing your specific questions in order:
So, how does this output travel from awk to bash?
A pipe to a spawned process.
Is this the expected behavior or a mere side effect?
Expected
Is there a better awk way to do it? Have tried asort and asorti already, but they exist with gawk and not awk.
Yes, pipe the output of the whole awk command to sort.
PS: I am trying to specifically write a .awk file for the task, without using bash commands. Please suggest the same.
See https://web.archive.org/web/20150928141114/http://awk.info/?Sorting for the implementation of a few common sorting algorithms in awk. See also https://rosettacode.org/wiki/Category:Sorting_Algorithms.
With respect to the question in your comments:
Since a process is spawned to sort from within the loop in the END rule, I was confused whether this will call the sort function on a single line and the spawned process will die there after, and a new process to sort will be spawned in the next iteration of the loop
The spawned process won't die until your awk script terminates or you call close("sort").

Answer 2

Could you please try changing you sort to sort -t',' -k1 in your code. Since your delimiter is comma so you need to inform sort that your delimiter is different than space. By default sort takes delimiter as comma.
Also you could remove if, else block ftom your main block and you could use only arr[$2]+=$3. Keep the rest code as it is apart from sort changes which I mentioned above
I am on mobile so couldn't paste all code but explanation should help you here.

Answer 3

What I would suggest is piping the output of awk to sort and not try and worry about piping the output within the END rule. While GNU awk provides asorti() to allow sorting the contents of an array, in this case since it is just the output you want sorted, a single pipe to sort after your awk script completes is all you need, e.g.
$ awk -F, -v OFS=, '{a[$2]+=$3}END{for(i in a)print i, a[i]}' file | sort
Birmingham,300
London,700
Mumbai,150
Seoul,450
Tokyo,1230
And since it is a single pipe of the output, you incur no per-iteration overhead for the subshell required by the pipe.
If you want to avoid the pipe altogether, if you have bash, you can simply use process-substitution with redirection, e.g.
$ sort < <(awk -F, -v OFS=, '{a[$2]+=$3}END{for(i in a)print i, a[i]}' file)
(same result)
If you have GNU awk, then asorti() will sort a by index and you can place the sorted array in a new array b and then output the sorted results within the END rule, e.g.
$ awk -F, -v OFS=, '{a[$2]+=$3}END{asorti(a,b);for(i in b)print b[i], a[b[i]]}' file
Birmingham,300
London,700
Mumbai,150
Seoul,450
Tokyo,1230