my $input = 'hello';
my $temp  = 'world';
$input = "$input $temp";

##</code><code>##

my $input = 'hello';
my $temp  = 'world';
$input = $input . ' ' . $temp;

##</code><code>##

my $input = 'hello';
my $temp  = 'world';
$input .= ' ' . $temp;

##</code><code>##

my $input = 'hello';
my $temp  = 'world';
$input = join(' ', $input,$temp);

##</code><code>##

my $input = 'hello';
my $temp  = 'world';
my @temp  = split('', $input);
push @temp, ' ';
push @temp, $_ for split('', $temp);
$input = join('',@temp);