You can silence the warning (if you know what you do) or you can detect and treat the undef-case. However, it is wise to keep the no warnings; scope small. Update: See also johngg's hint below about the do{ ... } trick.

When in doubt, I suggest to treat the undef-case, and let the warning pragma do its job. Often, an undef warning reveals a bug that was otherwise undetected. 

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 stri
+ng 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

[download]

In reply to Re: Annoying 'Use of uninitialized value in concatenation' warning by Perlbotics
in thread Annoying 'Use of uninitialized value in concatenation' warning by alain_desilets

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