If filename exists the first statements are executed. Otherwise the else statements are executed.
When label names are provided execution jumps to the specified label if the file specified in filename exists. If a second false label is specified, execution will jump to that label if the expression resolves false. Subroutine names can also be specified. When specifying a subroutine name execution will jump to that subroutine and return when the subroutine has completed. If label names are specified Else and Endif are ignored and are unnecessary.
Abbreviation : IFE