Examples of Boolean values in Perl programs

Examples illustrating concepts from
Computer Science & Perl Programming: Best of the Perl Journal
Edited by Jon Orwant
O'Reilly, 2003
Chapter 7: What is Truth, by Nathan Torkington

1. #!/usr/bin/perl -w
   
   # Test the truth value of an undefined variable
   
   if ($x) {
     print '$x is defined'."\n";
   } else {
     print '$x is undefined'."\n";
   }
   

2. #!/usr/bin/perl -w
   
   # Test the truth value of an empty string
   
   $x = "";
   if ($x) {
     print "an empty string is true\n";
   } else {
     print "an empty string is false\n";
   }
   

3. #!/usr/bin/perl -w
   
   # Test the truth value of integer zero
   
   $x = 0;
   if ($x) {
     print "integer zero is true\n";
   } else {
     print "integer zero is false\n";
   }
   

4. #!/usr/bin/perl -w
   
   # Test the truth value of floating point zero
   
   $x = 0.0;
   if ($x) {
     print "floating point zero is true\n";
   } else {
     print "floating point zero is false\n";
   }
   

5. #!/usr/bin/perl -w
   
   # Test the truth value of the string "0"
   
   $x = "0";
   if ($x) {
     print "the string \"0\" is true\n";
   } else {
     print "the string \"0\" is false\n";
   }