nandymamith has asked for the wisdom of the Perl Monks concerning the following question:

Am trying to compare two values, say $a = ''; $b = {}; if($a eq $b){ print "PASS"; } else { die "FAIL"; } May i know how to get the output as PASS ?? moreover i don't want get my out put as FAIL. In short how to compare the associative array($b) with the empty variable ($a)

  • Comment on How to compare an empty key with another empty key in associative array

Replies are listed 'Best First'.
Re: How to compare an empty key with another empty key in associative array
by bart (Canon) on Oct 24, 2012 at 11:06 UTC
    That sounds like you're coming from PHP. Well, OK, I'll write a little utility function empty which should look a bit familiar. That way you can compare if 2 values are both empty. 
    sub empty {
    my $r = shift;
    if(!ref $r) { return !$r }
    if(ref $r eq 'HASH') { return !keys %$r }
    if(ref $r eq 'ARRAY') { return !@$r }
    if(ref $r eq 'SCALAR') { return !$$r }
    return !1;    
}
$a = ''; $b = {}; $c = [];
if(empty($a) && empty($b) && empty($c)) { print "PASS"; }

    [download]
[reply]
[d/l]
[select]
Re: How to compare an empty key with another empty key in associative array
by DrHyde (Prior) on Oct 24, 2012 at 10:41 UTC
    '' and {} are different in just about every possible way. What you are trying to do is equivalent to comparing a strawberry and a moose and say that they're the same.
[reply]
[d/l]
[select]
Re: How to compare an empty key with another empty key in associative array
by 2teez (Vicar) on Oct 24, 2012 at 12:58 UTC

    Hi nandymamith,

    • $a = ''; $b = {};
      You really don't want to use $a and $b which are aliases for the two operands being compared in a sortsub.
    • That been said, $a and $b in above are two different things in perl. While $a is an empty scalar variable, $b is a reference to an anonymous hash, created using curly brackets which is empty in this case

      • However, in this case, you can compare these, printing what you want like so: 
      use warnings;
use strict;

my $empty_str = q{};
my $empty_hash_ref = { q{} => q{}, };

for ( keys %$empty_hash_ref ) {
    $empty_str eq $_ ? print "PASS" : print "FAIL";  ## print PASS
}

## use smartmarch ~~
$empty_str ~~ $empty_hash_ref ? print "PASS" : print "FAIL"; ## print 
+PASS

      [download]
    • Note however, that iterating through the hash comparing either the keys or values of the hash with the empty scalar variable, when the hash is empty ( with no variable atall) will print nothing, but using the smart match ~~ Operator will print "FAIL"
      • . 
        my $empty_str = q{};
  my $empty_hash_ref = {};  ## why?

   for (keys %$empty_hash_ref){
       $empty_str eq $_? print "PASS": print "FAIL"; # print nothing
   }

   $empty_str~~$empty_hash_ref?print "PASS": print "FAIL"; # print FAI
+L

      [download]

    Hope this helps

    If you tell me, I'll forget.
    If you show me, I'll remember.
    if you involve me, I'll understand.
    --- Author unknown to me
[reply]
[d/l]
[select]
Re: How to compare an empty key with another empty key in associative array
by Rudolf (Pilgrim) on Oct 24, 2012 at 11:50 UTC

    $b = {}; is not an associative array. An array containing other arrays may look something like this: 

    my @two_d_array = ([$x,$y,$z],[1,2,3],['a','b','c']);

    [download]

    To see if an array is empty, you can check it's scalar value for contents. 

    my $elements = scalar(@two_d_array);

    [download]

    UPDATED: Associative array is considered a hash in Perl, (thanks choroba),

[reply]
[d/l]
[select]
      "Associative array" is "hash" in Perl lingo, not an array.
      لսႽ† ᥲᥒ⚪⟊Ⴙᘓᖇ Ꮅᘓᖇ⎱ Ⴙᥲ𝇋ƙᘓᖇ
[reply]

Back to Seekers of Perl Wisdom