Shell Programming and Scripting

$ cat file.txt
A|X|20
A|Y|20
A|X|30
A|Z|20
B|X|10
A|Y|40

Summing up $NF based on first 2 fields,

$ awk -F "|" 'BEGIN {OFS="|"}
{ sum[$1 OFS $2] += $NF }
END { for (f in sum) print f,sum[f] }
' file.txt

o/p:

A|X|50
A|Y|60
A|Z|20
B|X|10

Works !!

Wondering if we can assign the "$1 OFS $2" part in some variable so that

$ var="$1 OFS $2"

And something like this will work 

$ awk -v x=$var -F "|" 'BEGIN {OFS="|"}
{ sum[x] += $NF }
END { for (f in sum) print f,sum[f] }
' file.txt

Presently its not working. The reason I have posted this : I have to sum based on a lot of fields and I want to make it kind of configurable outside awk. Please.

$ var="$1 OFS $2"

awk -v x=1 -v y=2  -F'|' '{ sum[ $x FS $y ] += $NF }  END { for (f in sum) print f, sum[f] }'  OFS='|' file

A|X|50
A|Y|60
A|Z|20
B|X|10

.....
{  A1[$1 OFS $2 OFS $3 OFS $4 ] += $7;A2[$1 OFS $2 OFS $3 OFS $4 ] += $8;A3[$1 OFS $2 OFS $3 OFS $4 ] += $9 ..................

awk 'BEGIN{OFS=FS=","}
{
key=sprintf("%s"OFS"%s"OFS"%s",$1,$2,$3)
a1[key]+=$4
a2[key]+=$5
}
END{
for(i in a1)
{
	print i" "a1[i]"  "a2[i]
}
}' filename