What does for (;;) mean in Perl?

Question

I was looking though a fellow developers code when I saw this ..

for (;;){
   ....
   ....
   ....
}

I have never seen ";;" used in a loop. What does this do exactly?

Answer 1

It loops forever. ';;' equates to no start value, no stop condition and no increment condition.

It is equivalent to

while (true)
{
   ...
}

There would usually be a conditional break; statement somewhere in the body of the loop unless it is something like a system idle loop or message pump.

Answer 2

All 3 parts are optional. An empty loop initialization and update is a noop. An empty terminating condition is an implicit true. It's essentially the same as

while (true) {
   //...
}

Note that you it doesn't have to be all-or-nothing; you can have some part and not others.

for (init; cond; ) {
  //...
}

for (; cond; update) {
  //...
}

for (init; ; update) {
  //...
}