You could extend bart's hash lookup by building a hash of arrays.

#!/usr/bin/perl

use strict;
use warnings;
use Data::Dumper;

my @list = qw{one two three four one};
my %lookup;
for my $i (0..$#list){
  push @{$lookup{$list[$i]}}, $i;
}

print "@{$lookup{one}}\n";

#print Dumper \%lookup;
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