=over

=item use Module LIST

=item use Module

=item use Module VERSION LIST

=item use VERSION

Imports some semantics into the current package from the named module,
generally by aliasing certain subroutine or variable names into your
package.  It is exactly equivalent to

    BEGIN { require Module; import Module LIST; }

except that Module I<must> be a bareword.

If the first argument to C<use> is a number, it is treated as a version
number instead of a module name.  If the version of the Perl interpreter
is less than VERSION, then an error message is printed and Perl exits
immediately.  This is often useful if you need to check the current
Perl version before C<use>ing library modules that have changed in
incompatible ways from older versions of Perl.  (We try not to do
this more than we have to.)

The C<BEGIN> forces the C<require> and C<import()> to happen at compile time.  The
C<require> makes sure the module is loaded into memory if it hasn't been
yet.  The C<import()> is not a builtin--it's just an ordinary static method
call into the "C<Module>" package to tell the module to import the list of
features back into the current package.  The module can implement its
C<import()> method any way it likes, though most modules just choose to
derive their C<import()> method via inheritance from the C<Exporter> class that
is defined in the C<Exporter> module.  See L<Exporter>.  If no C<import()>
method can be found then the error is currently silently ignored.  This
may change to a fatal error in a future version.

If you don't want your namespace altered, explicitly supply an empty list:

    use Module ();

That is exactly equivalent to

    BEGIN { require Module }

If the VERSION argument is present between Module and LIST, then the
C<use> will call the VERSION method in class Module with the given
version as an argument.  The default VERSION method, inherited from
the Universal class, croaks if the given version is larger than the
value of the variable C<$Module::VERSION>.  (Note that there is not a
comma after VERSION!)

Because this is a wide-open interface, pragmas (compiler directives)
are also implemented this way.  Currently implemented pragmas are:

    use integer;
    use diagnostics;
    use sigtrap qw(SEGV BUS);
    use strict  qw(subs vars refs);
    use subs    qw(afunc blurfl);

Some of these these pseudo-modules import semantics into the current
block scope (like C<strict> or C<integer>, unlike ordinary modules,
which import symbols into the current package (which are effective
through the end of the file).

There's a corresponding "C<no>" command that unimports meanings imported
by C<use>, i.e., it calls C<unimport Module LIST> instead of C<import()>.

    no integer;
    no strict 'refs';

If no C<unimport()> method can be found the call fails with a fatal error.

See L<perlmod> for a list of standard modules and pragmas.

=back