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

Quick and dirty Perl for you:

$lastfile = '';
while (<>) {
  @line = split(/\s+/);
  $filename = $line[1];
  print "\n" unless ($lastfile eq $filename);
  $lastfile = $filename;
  print;
}

Usage: perl script.pl < original_file.txt > newfile.txt