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Asserts a dependency of some kind depending on its argument. (If an argument is not supplied, $_ is used.)

If the argument is a string filename , this function includes and executes the Perl code found in the separate file of that name. This is similar to performing an eval on the contents of the file, except that require checks to see that the library file has not been included already. The function also knows how to search the include path stored in the @INC array.

If require s argument is a number num , the version number of the currently executing Perl binary (as known by $] ) is compared to num , and if smaller, execution is immediately aborted. Thus, a script that requires Perl version 5.003 can have as its first line:

require 5.003;
and earlier versions of Perl will abort.

If require s argument is a package name, require assumes an automatic .pm suffix, making it easy to load standard modules. This is like use , except that it happens at runtime, not compile time, and the import routine is not called.