require VERSION
require EXPR
require
Demands a version of Perl specified by VERSION, or demands some semantics specified by EXPR or by $_ if EXPR is not supplied.
VERSION may be either a numeric argument such as 5.006, which will be compared to $] , or a literal of the form v5.6.1, which will be compared to $^V (aka $PERL_VERSION). An exception is raised if VERSION is greater than the version of the current Perl interpreter. Compare with use, which can do a similar check at compile time.
Specif