next is a loop control which reevaluates the condition, which is false now.

It's no goto, you can only use if for lables just in front of loop-starts, OTOH gotos can jump to any lables in the same scope.

For your purpose better try redo

> perl
{
  print $x++;
  redo if $x<6;
}
__END__
012345
[download]

> perl
X: 
{
  print $x++;
  goto X if $x<6;
}
__END__
012345
[download]

UPDATES:

¹)from perlsyn

       Basic BLOCKs
 
       A BLOCK by itself (labeled or not) is semantically equivalent t
+o a loop
       that executes once.  Thus you can use any of the loop control
       statements in it to leave or restart the block.
[download]

I thought next is just another way to say goto

Well, it's not. You can see that next and goto compile to different ops internally:

$ perl -MO=Concise -e 'X: next X'
4  <@> leave[1 ref] vKP/REFC ->(end)
1     <0> enter ->2
2     <;> nextstate(X: main 1 -e:1) v:{ ->3
3     <"> next("X") v ->4
-e syntax OK
$ perl -MO=Concise -e 'X: goto X'
4  <@> leave[1 ref] vKP/REFC ->(end)
1     <0> enter ->2
2     <;> nextstate(X: main 1 -e:1) v:{ ->3
3     <"> goto("X") v ->4
-e syntax OK
[download]

Another difference is this warning here:

$ perl -wE 'sub f() { next X }; X: for (1) { f }'
Exiting subroutine via next at -e line 1.
[download]

which you don't get with goto. And of course the fact that the code above terminates, but doesn't if you replace 'next' with 'goto'.

I’m of the opinion that this sort of thing is the very worst kind of “Perl Golf” ... a game with all water-traps and no tee.   The construct is intended to go directly to the next iteration of a “real loop” as designated by the specified label-name.   If you are caught using it where no such loop exists (in the eyes of your co-workers, not Perl), and even if it so happens that Perl’s compiler accepts it, then you nevertheless richly deserve to be designated the one who gets to clean the coffee maker for the next full year.

(Urgh:   you do clean the coffee maker, don’t you??)

The OP asked "How does next label work?" and provided an edge case example to emphasize his problem.

Well that's perfectly normal ...and a well documented behavior is hardly "golf".

And BTW Basic BLOCKs with redo at the end

{ 
  ... ; 
  redo if COND; 
}
[download]

are a far saner way to realize do-while-loops.

do {
  ...
} 
while (COND)
[download]

EDIT:

I’m of the opinion that especially those coworkers which can't use perldoc -f should be restricted to clean the coffee maker. ;-)

Cheers Rolf

I'm of the opinion that this sort of thing is the very worst kind of "Perl Golf"

Though it's been a while since I've agreed with your opinion, I strongly agree with you this time. It is shockingly bad golf; the label in "next label" is clearly unnecessary, an outrageous waste of precious strokes.

... and it is also reason enough to say that one should never, ever make coffee in the office.   Always go to Starbuck’s and order a triple-shot.   Because you never know when something sentient might emerge from the unwashed office coffee-pot ...