Do I always/never have to quote my strings or use semicolons and commas?

Normally, a bareword doesn't need to be quoted, but in most cases probably should be (and must be under use strict). But a hash key consisting of a simple word (that isn't the name of a defined subroutine) and the left-hand operand to the => operator both count as though they were quoted: 

    This                    is like this
    ------------            ---------------
    $foo{line}              $foo{"line"}
    bar => stuff            "bar" => stuff

The final semicolon in a block is optional, as is the final comma in a list. Good style (see the perlsty manpage) says to put them in except for one-liners: 

    if ($whoops) { exit 1 }
    @nums = (1, 2, 3);


    if ($whoops) {
        exit 1;
    }
    @lines = (
	"There Beren came from mountains cold",
	"And lost he wandered under leaves",
    );