It's useful to be able to do different things in a manifest depending on the value of some variable or expression. Puppet provides several ways to do this. The first is the if statement.
An if statement has the
following form:
if EXPRESSION {
OPTIONAL_SOMETHING
}The part of the manifest represented by OPTIONAL_SOMETHING
will only be applied if the value of EXPRESSION is true. We'll learn more about expressions later in the chapter, but for now let's take a simple example:
if $eggs == 61 {
notify { 'Glory be, eggs have just gone up to 61¢ a dozen!': }
}Here the EXPRESSION is:
$eggs == 61
The == operator means "is equal to".
Note
Note the difference between $eggs == 61 and $eggs = 61
$eggs = 61 has a different meaning to Puppet. The single = operator has the effect of assigning the value 61 to the variable $eggs, while the double == operator tests equality. So in conditional expressions—expressions in an if statement, for example—we always use ==, not =.
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