sub a { 
     print "letter a";
}

sub b {
     print "letter b";
}

sub mother_mary {
     print "whispers softly";
}
1;

##</code><code>##

require Foo;

mother_mary();
print " ";
b();
print "\n";



##</code><code>##

$ perl require.pl 
whispers softly Letter B

##</code><code>##

package Foo;
sub a{
        print "Letter A";
}
sub b{
        print "Letter B";
}
sub mother_mary {
        print "whispers softly";

}
1;


##</code><code>##

$ perl require.pl 
Undefined subroutine &main::mother_mary called at require.pl line 3.