Add blank line between lines from different groups

Question

I have a file A of the form (frequency,file name,code lines):

1 file_name1 code_line1
2 file_name2 code_line2
2 file_name2 code_line3
2 file_nam         


        

Answer 1

You can use Awk:

awk 'BEGIN{file=0}{if (file && file!=$2) {print ""} print $0; file=$2}' fileA