Putting 2 consecutive lines of same matching pattern into single line

Question

I want to parse this set of lines so that if get the same pattern like **** in consecutive lines, it should print it in single with

Answer 1

With lookaround:

#!/usr/bin/env perl
use strict;
use warnings;

my $str = <<'EOS';
q2VDWKkY010407  2221878 Sat Mar 31 19:37 <Mailer-daemon>
                     (host map: lookup (my.local.domain): deferred)
                                             <yagyavalkbhatt@yahoo.com>
                                             <yagyavalkbhatt@yahoo.com>
q2VDWKkY010407  2221878 Sat Mar 31 19:37 <Mailer-daemon>
                     (host map: lookup (my.local.domain): deferred)
                                             <yagyavalkbhatt@yahoo.com>
                                             <yagyavalkbhatt@yahoo.com>
EOS

$str =~ s/(?<=<yagyavalkbhatt\@yahoo.com>)\s+(?=<yagyavalkbhatt\@yahoo.com>)/,/g;
print $str;

Output:

q2VDWKkY010407  2221878 Sat Mar 31 19:37 <Mailer-daemon>
                 (host map: lookup (my.local.domain): deferred)
                                         <yagyavalkbhatt@yahoo.com>,<yagyavalkbhatt@yahoo.com>
q2VDWKkY010407  2221878 Sat Mar 31 19:37 <Mailer-daemon>
                 (host map: lookup (my.local.domain): deferred)
                                         <yagyavalkbhatt@yahoo.com>,<yagyavalkbhatt@yahoo.com>