As already mentioned by JavaFun, "B::Deparse" shows that perl compiles "while(){}" and "for(;;){}" to the same code, so "1" and "2" behave different, "3" and "4" are equal, "5" and "6" are also equal ...

#!/usr/bin/perl

use B::Deparse;

my $deparse = B::Deparse->new();

my $sub0 = sub {
    for(;;) {print};
};

my $sub1 = sub {
    while () {print};
};

my $sub2 = sub {
    while ( () ) {print};
};

my $sub3 = sub {
    print while ();
};

my $sub4 = sub {
    print while ( () );
};

my $sub5 = sub {
    print until ();
};

my $sub6 = sub {
    print until ( () );
};

foreach ( $sub0, $sub1, $sub2, $sub3, $sub4, $sub5, $sub6 ) {
    print $count++,":\nsub ", $deparse->coderef2text($_), "\n\n";
}
[download]

Program output:

0:
sub {
    while (1) {
        print $_;
    }
}

1:
sub {
    while (1) {
        print $_;
    }
}

2:
sub {
    while (()) {
        print $_;
    }
}

3:
sub {
    print $_ while ();
}

4:
sub {
    print $_ while ();
}

5:
sub {
    print $_ until ();
}

6:
sub {
    print $_ until ();
}
[download]

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