eval can evaluate either a block of code or a character string containing code. It returns the return value of that code (last computed value in the block/string).

$x = 1;
$y = 2;
$code = "$x + $y";
print $code;
print eval $code;
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First print yields "1 + 2", second print yields "3".

Also, yes, eval sets the global variable $@ to be the value of any exception that was thrown inside of the eval.