Evaluates boolean expression cond-1, and if true executes the block of code body-1. If cond-1 is false, then cond-2 is evaluated (if present) and if true body-2 will be executed. This is repeated for each elseif condition in order until one of the conditions is found to be true. If none of the conditionals are true, then the else-body will be executed.

The else and elseif clauses are optional. Any number of elseif clauses may be specified, but only one else, which must be the last clause in the sequence. Any of the bodys may be empty.

If an if expression contains an else clause and the body of every clause produces a value or ends with a statement that does not return (e.g. throw or error or proc declared to return never-returns), then the if expression will produce the value of the body for the branch that is executed. In this case, the if expression may be used in places where values are expected such as the right hand side of an assignment or as an argument to a function.

For examples and a more detailed discussion of if and other conditional forms in Curl see Conditional Constructs in The Developers Guide.