Count b or B in even lines

Question

I need count the number of times in the even lines of the file.txt the letter 'b' or 'B' appears, e.g. for the file.txt like:

everyB or gbnBra
uitiakB and kanapB bodddB
Kanbalis astroBominus

I got the first part but I need to count these b or B letters and I do not know how to count them together

awk '!(NR%2)' file.txt

Answer 1

$ awk '!(NR%2){print gsub(/[bB]/,"")}' file
4

Answer 2

Could you please try following, one more approach with awk written on mobile will try it in few mins should work but.

awk -F'[bB]' 'NR%2 == 0{print (NF ? NF - 1 : 0)}' Input_file

Thanks to @Ed sir for solving zero matches found line problem in comments.

Answer 3

In a single awk:

awk '!(NR%2){gsub(/[^Bb]/,"");print length}' file.txt

gsub(/[^Bb]/,"") deletes every character in the line the line except for B and b.

print length prints the length of the resulting string.