while (my $line = <>) ... Similarly, ... while (my $item = pop @my_array)

use warnings;
use strict;

while (my $line = <DATA>) {
    chomp $line;
    print "<$line>\n";
}

my @array = ("Foo","0","Bar");
while (my $item = pop @array) {
    print "[$item]\n";
}

__DATA__
Hello
0

World
[download]

Outputs:

<Hello>
<0>
<>
<World>
[Bar]
[download]

I'd call that a pretty serious caveat. As per I/O Operators, the first is equivalent to while ( defined( my $line = <> ) ), and readline returns undef at EOF, while the second one will stop at any false value, and arrays can contain undefs too.