my @lines = qw(foo foo2foo bar bar2bar baz2 bell bell1bell);
print "Method 1\n";

for my $i (0..$#lines){
  if ( $lines[$i] =~ /2/ ){
    print "$lines[$i], $lines[$i + 1]\n";
  }
}

print "\n\nMethod 2\n";

for (my $i=0; $i <= $#lines; $i++){
  if ( $lines[$i] =~ /2/ ){
    print "$lines[$i], $lines[$i + 1]\n";
    $i++;
  }
}