space in variable referencing

Question from a newbie: how to properly use space
when reference to variables, array, hash etc.

please see the code below:
why the first line, second, and third line all output differiently.
thanks.
ciwei

========code below ======
#!/usr/bin/perl

my %ttys =();
open ( WHO, "who|") or die "can;t \n";

while ( <WHO> ){

( $user, $tty ) = split ;
push @{$ttys{ $user}} , $tty;

}

foreach $user ( sort keys %ttys ){

print "first line : $user => @{$ttys {$user}} \n";
print "second line: $user => @ {$ttys { $user}} \n";
print "third line: $user => @{$ttys{$user}} \n";

}

__OUTPUT__
first line : root =>
second line: root => @ { { root}}
third line: root => pts/1 pts/4 pts/6 pts/7 pts/8

.

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