in reply to Find all keys from a value in a hash

You basically need to maintain a membership map as an index of values, the reverse look up referred to below: 
my $search = "red";

my %fruit = (
   'apple' => ['red','green'],
   'kiwi' => 'green',
   'banana' => 'yellow',
  );

my %idx_fruit = (
    'red'    => {'apple' => 1 },
    'green'  => {'apple' => 1, 'kiwi' => 1 },
    'yellow' => {'banana' => 1},
  );

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Note: %idx_fruit is a hash, but contains members as hash references. This is to provide natural semantics for managing the membership sets and accessing values (e.g., delete, exists, etc). The value => 1 is meaningless, but might be useful for some additional meta data. You could even have them point to the reference of the member in %fruit for maximized fun.

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Re^2: Find all keys from a value in a hash
by Anonymous Monk on Nov 11, 2021 at 14:11 UTC
    I came up with this:
    #!/usr/bin/perl

use strict;
use warnings;

my $search = $ARGV[0] || '';

if(!$search) {
  print   "\n\n Need a color word to search! \n\n";
  exit;
}

my %fruit = (
   'apple'   => ['red','green'],
   'kiwi'    => ['blue'],
   'banana'  => ['yellow'],
   'avocato' => ['brown'],
  );


my ($result) = grep { grep { $_ eq $search } @{$fruit{$_}} } keys %fru
+it;

print "\n\n Result:::: --> $result \n\n";

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[d/l]
      One thing that I like about this approach is to use anon ref's to array for all of the values if any key can be associated with more than a single color. This eliminates the checking of "if ref".
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