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Boolean in Perl


Perl does not have a special "Boolean" type. But Perl often returns true or false.

In Perl, every expression is considered true except for the following cases:

  • Number 0.
  • Empty string ("")
  • undef - undefined (The value of a variable is undef if it is not initialized.)
  • '0' - String containing a single 0 digit

Now, see this chart for general Boolean operations:

Exp1 Operator Exp2 Boolean
True AND True True
True AND False False
False AND False False
True OR True True
True OR False True
False OR False False

So, if we use AND with any two operands and if both of them are True, then the result is True. Otherwise, it is False
And if we use OR and if any of the two operands is True, then the result is True and it is False if both the operands are False.

'AND' can be understood as both ( first and second both )
'OR' can be understood as either ( any of the first or second ). See the next line to understand it more clearly.
True OR False -> As 'OR' is used, either of the two is true -> True
True AND False -> As 'AND' is used, both are not true -> False

Try to understand this or just remember the chart.

Now, let's use these in a mathematical operation to understand their use. So, 2>5 AND 10>7 is False. (2>5 is False, 10>7 is True)
2>5 OR 10>7 is True.

NOT


NOT reverses the value of a Boolean. It means that NOT(True) is False and NOT(False) is True.

I hope that now you know about Booleans and their uses. So, let's use these in Perl.

Operators used in Perl for this purpose are:

Assume that 'a' is true and 'b' is false.

Operator Description Example
&& C-style Logical AND operator ($a && $b) is false
|| C-style Logical OR operator ($a || $b) is true
and Logical AND operator ($a and $b) is false
or Logical OR operator ($a or $b) is true
! C-style Logical NOT operator !($a) is false
not Logical NOT operator not($a) is false

Let's see an example of these operators:

$a = true;
$b = false;
$c = ($a and $b);
print $c,"\n";
$c = ($a && $b);
print $c,"\n";
$c = ($a or $b);
print $c,"\n";
$c = ($a || $b);
print $c,"\n";
$a = 0;
print !($a),"\n";
$c = not($a);
print $c,"\n";
Output
false
false
true
true
1
1

You will learn about different operators in the next chapter.

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