Perl && do { last; };

In my book it uses something like this:

for($ARGV[0])
{
Expression && do { print "..."; last; };
...
}

Isn't the for-loop incomplete? Also, what's the point of the do, couldn't it just be {开发者_如何学编程 ... }, or does the do have some importance here?

There are two forms of for statement in Perl. The one you're seeing here is often written as foreach, but for and foreach are synonyms. It normally iterates over a list, setting $_ to each element. In this case, the "list" is a single value, so it has the effect of setting $_ to $ARGV[0] for the body of the loop.

The do is needed to make the block { ... } into an expression, so it can be an operand of the && operator. (See what happens if you omit the word do.)

(And you were missing a semicolon; I've edited the question to fix that.)