cat filename.txt | grep x_y | (this need to be filled)

perl -pi -e 's/x_y/m_n/g'

perl -nE '$s+=$1, ++$n if /x_y=(d+)/; END { say "avg:", $s/$n }' data.txt

... | grep 'x_y=' | perl -ne '$x += (split /=/, $_)[1]; $y++ }{ print $x/$y, "n"'

/^[^_]+_[^=]+=[0-9]+$/ {sum=sum+$2; cnt++}
END {
    print "sum:", sum, "items:", cnt, "avg:", sum/cnt
}

$ awk -F= -f cnt.awk data.txt
sum: 55 items: 10 avg: 5.5

#!/bin/bash

while IFS='=' read str num
do
    if [[ $str == *_* ]]
    then
        sum=$((sum + num))
        cnt=$((cnt + 1))
    fi

done < data.txt

echo "scale=4; $sum/$cnt" | bc ;exit

$ ./cnt.sh
5.5000

perl -nlwe '
    push @a, /x_y=(d+)/g          # push all matches onto an array
    }{                             # eskimo-operator, is evaluated last
    $sum += $_ for @a;             # get the sum
    print "Average: ", $sum / @a;  # divide by the size of the array
' input.txt

perl -nlwe 'push @a, /x_y=(d+)/g }{ $sum += $_ for @a; print "Average: ", $sum / @a;' input.txt