Here's one of many ways. Caveat, if any of your commands or locations contain '|', use a character they don't contain.

my @array = ( 'north#library' , 'south#kitchen', 'east#hallway');
my $cmd = 'south';
(my $location) = join('|', @array) =~ m[$cmd\#(.*?)\|];
print $location;

kitchen
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