note
Roy Johnson
Here's a demo of a sub you might find useful. It descends the hash chain checking existence at each level. It returns [a reference to, to ensure logical truth] the value if everything exists.
<code>
#!perl
use warnings;
use strict;
sub safe_exists {
my ($href, @list_of_descent) = @_;
use List::Util 'first';
if (first {
not (exists $href->{$_} and $href=$href->{$_})
} @list_of_descent) {
return ();
}
else {
return \$href;
}
}
my %hash = ('a' => {
'value' => 1,
'foo' => 'bar',
},
'b' => {
'value' => 2,
'foo' => 'bar',
},
'c' => {
'value' => 3,
'foo' => 'bar',
},
);
for (qw(a b c d)) {
if (my $href = safe_exists(\%hash, $_, 'value')) {
print "$_ value is $$href\n";
}
else {
print "Key $_ doesn't exist. Valid keys are: ";
print join (", ", keys %hash), "\n";
}
}</code>
<!-- Node text goes above. Div tags should contain sig only -->
<div class="pmsig"><div class="pmsig-300037">
<hr>
<small><b>Caution:</b> Contents may have been coded under pressure.</small>
</div></div>
451791
451791