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2.6. The if Control StructureOnce you can compare two values,you'll probably want your program to make decisions based upon that comparison. Like all similar languages,Perl has an if control structure: if ($name gt 'fred') {
print "'$name' comes after 'fred' in sorted order./n";
}
If you need an alternative choice,the else keyword provides that as well: if ($name gt 'fred') {
print "'$name' comes after 'fred' in sorted order./n";
} else {
print "'$name' does not come after 'fred'./n";
print "Maybe it's the same string,in fact./n";
}
Those block curly braces are required around the conditional code (unlike C,whether you kNow C or not). It's a good idea to indent the contents of the blocks of code as we show here; that makes it easier to see what's going on. If you're using a programmers' text editor (as discussed in Chapter 1),it'll do most of the work for you. 2.6.1. Boolean ValuesYou may use any scalar value as the conditional of the if control structure. That's handy if you want to store a true or false value into a variable,like this: $is_bigger = $name gt 'fred';
if ($is_bigger) { ... }
But how does Perl decide whether a given value is true or false? Perl doesn't have a separate Boolean data type as some languages have. Instead,it uses a few simple rules:[*]
There's one trick hidden in those rules. Because the string '0' is the same scalar value as the number 0,Perl has to treat them the same. That means that the string '0' is the only nonempty string that is false. If you need to get the opposite of any Boolean value,use the unary not operator,!. If what follows it is a true value,it returns false; if what follows is false,it returns true: if (! $is_bigger) {
# Do something when $is_bigger is not true
}
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