Use of uninitialized value $FIXED_STRING in hash element at ... #### #!/usr/bin/env perl # demo of closure around sub, with persistent string use strict; use warnings; for my $q ('a'..'g') { do_something($q); print "Done computing\n" } { my $FIXED_STRING = 'fixed_string'; my %persistent; sub do_something { my $x = $_[0]; $persistent{$x}{$FIXED_STRING} = rand; END { for my $k (keys %persistent) { print "$k: $persistent{$k}{$FIXED_STRING}\n"; } } } }