Shell Programming and Scripting

File 1              File 2
line1               line1              |
line2               line2              | group 1
line3               line3              |

line1               line1              |
line2               line2              | group 2 

line1               line1              | group 3
.                    .
.                    .
.                    .

line n              line n              | group n

line1 (file1)
line2 (file1)
line3 (file1)
line1 (file2)
line2 (file2)
line3 (file2)
<blank line>
line1 (file1)
line2 (file1)
line1 (file2)
line2 (file2)
<blank line>
line n (file1)
line n (file2)
<blank line>

#!/usr/bin/perl
use strict;
use warnings;
my $file1=open_file("file1.txt");
my $file2=open_file("file2.txt");
my @file1 = split(/\n{2,}/, $file1);
my @file2 = split(/\n{2,}/, $file2);
for (my $i = 0; $i<=$#file1; $i++) {
print "\n----- Group ", $i+1," ------\n", "$file1[$i]\n", "$file2[$i]\n";
}
sub open_file
{
 my ($fname)=@_;
 undef $/;
 open (FIN, "<", "$fname") || die "Cannot open the input file $fname : $!";
 my $fcontent=<FIN>;
 close (FIN);
 return "$fcontent\n";
}