Perl - Boolean Expressions

In a Nutshell - CIW Course Section 2, Part B1, Chapter 3

Boolean Expressions

A Boolean expression is an expression that evaluates to a true or false value. However, in Perl, if an expression evaluates to false nothing is returned. So, in Perl a Boolean Expression will evaluate to true (1) or nothing.

Numeric Boolean Expressions

When comparing two numeric values, Perl has a number of numeric Boolean operators to make the comparison.

Numeric Boolean Operators
Operator	Description
= =	Equal to
!=	Not equal to
>	Greater than
>=	Greater than or equal to
<	Less than
<=	Less than or equal to

When making a Boolean comparison, the left operand is compared to the right operand and true will be returned if the comparison condition is met.

String Boolean Expressions

String comparisons are done in the same way as numeric comparisons, but use a different set of operators.

String Boolean Operators
Operator	Description
eq	Equal to
ne	Not equal to
gt	Greater than
ge	Greater than or equal to
lt	Less than
le	Less than or equal to

I did a little experimenting to see how these comparisons are reached, and discovered that it only seems to compare the first character of the string, unless the initial characters are the same.

"sam" is less than "tom", "sww" is less than "tom" and "tom" is less than "tommy".

Logical Operators

Logical operators allow the combining of Boolean expressions to provide greater flexibility and more advanced decision making.

Logical Operators
Operator	Logical	Description
&&	AND	Both expression1 and expression2 must be true
xor	XOR	Only expression1 or expression2 must be true
\| \|	OR	If both expression1 and expression2 are false the logical will return false
! (exclamation)	NOT	Inverts the logical value of the operand to it's right

Syntax is: expression1 <logical> expression2

Example: If ($a = 10 && $b = 5) {