use strict; use warnings; sub original_post { my @some_array = (1, 2, undef, 4, 5); for (my $ii=0; $ii < scalar(@some_array); $ii++) { print "Value at position $ii: $some_array[$ii]\n"; } } sub detect_undef_and_set { my @some_array = (1, 2, undef, 4, 5); #alternative-1: fix data structure # @some_array = map { $_ // '(oops! undef!!)' } @some_array; for (my $ii=0; $ii < scalar(@some_array); $ii++) { #alternative-2: fix output print "Value at position $ii: ", $some_array[$ii] // '(oops! undef!)' , "\n"; } } sub no_warnings { my @some_array = (1, 2, undef, 4, 5); for (my $ii=0; $ii < scalar(@some_array); $ii++) { no warnings 'uninitialized'; # for this lex scope only print "Value at position $ii: $some_array[$ii]\n"; } } print "ORIG:\n"; original_post(); print "CHECK:\n"; detect_undef_and_set(); print "NO WARN:\n"; no_warnings(); __DATA__ RIG: Value at position 0: 1 Value at position 1: 2 Use of uninitialized value $some_array[2] in concatenation (.) or string at nowarn.pl line 7. Value at position 2: Value at position 3: 4 Value at position 4: 5 CHECK: Value at position 0: 1 Value at position 1: 2 Value at position 2: (oops! undef!) Value at position 3: 4 Value at position 4: 5 NO WARN: Value at position 0: 1 Value at position 1: 2 Value at position 2: Value at position 3: 4 Value at position 4: 5