in reply to Undefined vs empty string

Depends somewhat on what you are going to do in the body og the if, but defined and length will generally ensure that a variable is defined and contains something; so negate that: 

say "'$_'", ' ', !(defined and length) ? 'go' : 'nogo' for undef, '', 
+0, 'fred';;
Use of uninitialized value $_ in concatenation (.) or string at (eval 
+16) line 1, <STDIN> line 8.
''   go
''   go
'0'   nogo
'fred'   nogo

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Re^2: Undefined vs empty string
by Anonymous Monk on Jun 05, 2013 at 02:48 UTC
    So if my intention is to ensure that a variable is defined and contains something, should I change my code to how you have recommended or what I have is OK?
[reply]

      Much of a muchness. length is a tiny bit quicker than eq, but otherwise I think they will act similarly.

      With the rise and rise of 'Social' network sites: 'Computers are making people easier to use everyday'
      Examine what is said, not who speaks -- Silence betokens consent -- Love the truth but pardon error.
      "Science is about questioning the status quo. Questioning authority".
      In the absence of evidence, opinion is indistinguishable from prejudice.
[reply]

        Speed very much depends on what is the most likely value to occur in the tests. length for sure is not always faster. I prefer using defined-or:

        $ cat test.pl
use 5.014;
use warnings;
use Benchmark qw(cmpthese);

foreach $a (undef, "", 0, 1, "x" x 60) {
    say "Testing for a = ", $a // "undef";

    cmpthese (-1, {
    def_eq  => sub { for (0..1000) { ! defined $a || $a eq ""   ? 1 : 
+0; }},
    def_len => sub { for (0..1000) { !(defined $a && length $a) ? 1 : 
+0; }},
    dor_eq  => sub { for (0..1000) { ($a // "") eq ""           ? 1 : 
+0; }},
    });
    }
$ perl test.pl
Testing for a = undef
           Rate  dor_eq  def_eq def_len
dor_eq   9135/s      --    -21%    -21%
def_eq  11499/s     26%      --     -1%
def_len 11605/s     27%      1%      --
Testing for a =
          Rate def_len  def_eq  dor_eq
def_len 7110/s      --     -8%    -25%
def_eq  7729/s      9%      --    -19%
dor_eq  9489/s     33%     23%      --
Testing for a = 0
           Rate def_len  def_eq  dor_eq
def_len  7518/s      --    -12%    -29%
def_eq   8533/s     14%      --    -19%
dor_eq  10577/s     41%     24%      --
Testing for a = 1
           Rate def_len  def_eq  dor_eq
def_len  7518/s      --    -12%    -29%
def_eq   8533/s     14%      --    -19%
dor_eq  10577/s     41%     24%      --
Testing for a = xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
+xxxxxx
           Rate def_len  def_eq  dor_eq
def_len  7450/s      --    -13%    -30%
def_eq   8533/s     15%      --    -20%
dor_eq  10676/s     43%     25%      --
$

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        Enjoy, Have FUN! H.Merijn
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