Programming Perl, 4th Edition

prototype

prototype FUNCTION

This function returns the prototype of a function as a string (or undef if the function has no prototype). FUNCTION is a reference to, or the name of, the function whose prototype you want to retrieve.

If FUNCTION is a string starting with CORE::, the rest is taken as a name for a Perl built-in, and an exception is raised if there is no such built-in. If the built-in is not overridable (such as qw//) or its arguments cannot be expressed by a prototype (such as system), the function returns undef because the built-in does not really behave like a Perl function. Otherwise, the string describing the equivalent prototype is returned.