6.2. Mixing Data Types

If you have operands of mixed types (i.e., numbers and strings), Perl will make the appropriate conversion by testing whether the operator expects a number or a string for an operand. This is called overloading the operator.

If the operator is a numeric operator, such as an arithmetic operator, and the operand(s) is a string, Perl will convert the string to a decimal floating point value. Undefined values will become zero. If there is leading whitespace or trailing non-numeric characters, they will be ignored, and if a string cannot be converted to a number, it will be converted to zero.

          $string1 = "5 dogs ";
          $string2 = 4;
          $number = $string1 + $string2;  # Numeric context
          print "Number is $number.\n";   # Result is  9

Likewise, if Perl encounters a string operator and the operand(s) is numeric, Perl will treat the number as a string. The concatenation operator, for example, expects to join two strings together.

         $number1 = 55;
         $number2 = "22";
         $string = $number1 . $number2;  # Context is string
         print "String is string.\n"     # Result is "5522"

Table 6.1. How Strings Are Converted to Numbers

String	Converts to	Number
"123 go!"		123
"hi therev		0
"4e3"		4000
"-6**3xyz"		-6
" .456!!"		0.456
"x.1234"		0
"0xf"		0

Example 6.1.

(The Script) 1 $x = " 12hello!!" + "4abc\n"; # Perl will remove leading whitespace and trailing non-numeric # characters 2 print "$x"; 3 print "\n"; 4 $y = ZAP . 5.5; 5 print "$y\n"; (Output) 2 16 5 ZAP5.5 Explanation The plus sign (+) is a numeric operator. The strings " 12hello!!" and "4abc\n" are converted to numbers (leading whitespace and trailing non-numeric characters are removed) and addition is performed. The result is stored in the scalar $x. The scalar $x is printed. Since the \n was stripped from the string 4\n in order to convert it to a number, another \n is needed to get the newline in the printout. The period (.), when surrounded by whitespace, is a string operator. It concatenates two strings. The number 5.5 is converted to a string and concatenated to the string ZAP. The value of the scalar $y is printed.