That's because the comma operator in scalar context returns the second argument. See perlop for details.

Update:

Also, one interesting case is missing in your question: 

my $t = '111', '222', 'aaa', 'bbb';
print $t;

[download]

It prints 111, becuase of precedence of the two operators involved, the comma and equal sign. In fact, the parentheses in the $s case were used only to change the precedence.

($q=q:Sq=~/;[c](.)(.)/;chr(-||-|5+lengthSq)`"S|oS2"`map{chr |+ord
}map{substrSq`S_+|`|}3E|-|`7**2-3:)=~y+S|`+$1,++print+eval$q,q,a,

[download]

In reply to Re: The behavior when assigning an array to scalar? by choroba
in thread The behavior when assigning an array to scalar? by fgg1991

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