BTW when you call each in scalar context it would only return the key, not the related value.

The keys function will help you sort the other question.

foreach $c (each %couples) {
   print "$c\n";
};
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each %couple returns, in list context, the next key/value pair. In this case (bacause the %hash is stored in "semi-random" order), returns the pair (abbot,costello). You can visualize this as:

foreach $c ("abbot","costello") {
   print "$c\n";
};
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The foreach prints then "abbot" and "costello".

The expected output can be obtained in list context, for example:

while (my ($c,$d) = each %couples){
  print "$c $d\n";
}
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The shorter way I could imagine to do this is:

print "$_ $couples{$_}$/" for (keys %couples);
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Hope this helps!

citromatik

Thank you, citromatik. When I implement some of your examples, I notice, now, another baffling action:

my %couples = (
  george => 'gracie',
  abbot => 'costello',
  johnson => 'boswell',);

while (my($c, $d) = each %couples) {
   print "$c $d\n";
}

print "\n";

foreach my $c (each %couples) {
  print "$c\n";
}

print "\n";

while ( my($c, $d) = each %couples) {
        print "$d $c\n";
}
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The first foreach example code you offered, when run prior to the first while loop you suggested, causes the while loop to drop one of the key, value pairs.The same while loop, run before the foreach loop, outputs all three key, value pairs.

What causes that behavior? Does the scope of the foreach loop manage to extend, in some way, to the following while loop?

Thanks, again, for helping with this.

"perldoc -f each" gives you the explanation:

When called in list context, returns a 2-element list consisting of the key and value for the next element of a hash, so that you can iterate over it. When called in scalar context, returns only the key for the next element in the hash.

(hmmm ... http://perldoc.perl.org appears to still be down)

For example:

#!/usr/local/bin/perl

use strict;
use warnings;

my %couples = (
   george  => 'gracie',
   abbot   => 'costello',
   johnson => 'boswell',
);

my( $key, $val );

# scalar context - return keys one at a time
$key = each %couples;
print "$key : $couples{$key}\n";

$key = each %couples;
print "$key : $couples{$key}\n";

$key = each %couples;
print "$key : $couples{$key}\n";

# reset each's internal iterator
$key = each %couples;

# list context
while ( ($key, $val) = each %couples ) {
  print "$key - $val\n";
}
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First time call: build an array of keys in even positions and their values in odd positions and then...

All calls: shift and return the first two values in stored array.

The single-operand for loop you show calls "each" only once irrespective of what is returned and so it builds an iteration list of only one key/value pair. The reason a while loop DWIMs on the other hand is that it keeps calling "each", picking up pairs until the array it "kept to itself" is exhausted.