The OpenNET Project / Index page

[ новости /+++ | форум | теги | ]

Интерактивная система просмотра системных руководств (man-ов)

 ТемаНаборКатегория 
 
 [Cписок руководств | Печать]

perlboot (1)
  • >> perlboot (1) ( Solaris man: Команды и прикладные программы пользовательского уровня )
  • perlboot (1) ( Разные man: Команды и прикладные программы пользовательского уровня )
  • 
    
    

    NAME

         perlboot - Beginner's Object-Oriented Tutorial
    
    
    

    DESCRIPTION

         If you're not familiar with objects from other languages,
         some of the other Perl object documentation may be a little
         daunting, such as the perlobj manpage, a basic reference in
         using objects, and the perltoot manpage, which introduces
         readers to the peculiarities of Perl's object system in a
         tutorial way.
    
         So, let's take a different approach, presuming no prior
         object experience. It helps if you know about subroutines
         (the perlsub manpage), references (the perlref manpage et.
         seq.), and packages (the perlmod manpage), so become
         familiar with those first if you haven't already.
    
         If we could talk to the animals...
    
         Let's let the animals talk for a moment:
    
             sub Cow::speak {
               print "a Cow goes moooo!\n";
             }
             sub Horse::speak {
               print "a Horse goes neigh!\n";
             }
             sub Sheep::speak {
               print "a Sheep goes baaaah!\n"
             }
    
             Cow::speak;
             Horse::speak;
             Sheep::speak;
    
         This results in:
    
             a Cow goes moooo!
             a Horse goes neigh!
             a Sheep goes baaaah!
    
         Nothing spectacular here.  Simple subroutines, albeit from
         separate packages, and called using the full package name.
         So let's create an entire pasture:
    
             # Cow::speak, Horse::speak, Sheep::speak as before
             @pasture = qw(Cow Cow Horse Sheep Sheep);
             foreach $animal (@pasture) {
               &{$animal."::speak"};
             }
    
         This results in:
             a Cow goes moooo!
             a Cow goes moooo!
             a Horse goes neigh!
             a Sheep goes baaaah!
             a Sheep goes baaaah!
    
         Wow.  That symbolic coderef de-referencing there is pretty
         nasty.  We're counting on `no strict subs' mode, certainly
         not recommended for larger programs.  And why was that
         necessary?  Because the name of the package seems to be
         inseparable from the name of the subroutine we want to
         invoke within that package.
    
         Or is it?
    
         Introducing the method invocation arrow
    
         For now, let's say that `Class->method' invokes subroutine
         `method' in package `Class'.  (Here, "Class" is used in its
         "category" meaning, not its "scholastic" meaning.) That's
         not completely accurate, but we'll do this one step at a
         time.  Now let's use it like so:
    
             # Cow::speak, Horse::speak, Sheep::speak as before
             Cow->speak;
             Horse->speak;
             Sheep->speak;
    
         And once again, this results in:
    
             a Cow goes moooo!
             a Horse goes neigh!
             a Sheep goes baaaah!
    
         That's not fun yet.  Same number of characters, all
         constant, no variables.  But yet, the parts are separable
         now.  Watch:
    
             $a = "Cow";
             $a->speak; # invokes Cow->speak
    
         Ahh!  Now that the package name has been parted from the
         subroutine name, we can use a variable package name.  And
         this time, we've got something that works even when `use
         strict refs' is enabled.
    
         Invoking a barnyard
    
         Let's take that new arrow invocation and put it back in the
         barnyard example:
    
    
             sub Cow::speak {
               print "a Cow goes moooo!\n";
             }
             sub Horse::speak {
               print "a Horse goes neigh!\n";
             }
             sub Sheep::speak {
               print "a Sheep goes baaaah!\n"
             }
    
             @pasture = qw(Cow Cow Horse Sheep Sheep);
             foreach $animal (@pasture) {
               $animal->speak;
             }
    
         There!  Now we have the animals all talking, and safely at
         that, without the use of symbolic coderefs.
    
         But look at all that common code.  Each of the `speak'
         routines has a similar structure: a `print' operator and a
         string that contains common text, except for two of the
         words.  It'd be nice if we could factor out the commonality,
         in case we decide later to change it all to `says' instead
         of `goes'.
    
         And we actually have a way of doing that without much fuss,
         but we have to hear a bit more about what the method
         invocation arrow is actually doing for us.
    
         The extra parameter of method invocation
    
         The invocation of:
    
             Class->method(@args)
    
         attempts to invoke subroutine `Class::method' as:
    
             Class::method("Class", @args);
    
         (If the subroutine can't be found, "inheritance" kicks in,
         but we'll get to that later.)  This means that we get the
         class name as the first parameter (the only parameter, if no
         arguments are given).  So we can rewrite the `Sheep'
         speaking subroutine as:
    
             sub Sheep::speak {
               my $class = shift;
               print "a $class goes baaaah!\n";
             }
    
         And the other two animals come out similarly:
    
             sub Cow::speak {
               my $class = shift;
               print "a $class goes moooo!\n";
             }
             sub Horse::speak {
               my $class = shift;
               print "a $class goes neigh!\n";
             }
    
         In each case, `$class' will get the value appropriate for
         that subroutine.  But once again, we have a lot of similar
         structure.  Can we factor that out even further?  Yes, by
         calling another method in the same class.
    
         Calling a second method to simplify things
    
         Let's call out from `speak' to a helper method called
         `sound'.  This method provides the constant text for the
         sound itself.
    
             { package Cow;
               sub sound { "moooo" }
               sub speak {
                 my $class = shift;
                 print "a $class goes ", $class->sound, "!\n"
               }
             }
    
         Now, when we call `Cow->speak', we get a `$class' of `Cow'
         in `speak'.  This in turn selects the `Cow->sound' method,
         which returns `moooo'.  But how different would this be for
         the `Horse'?
    
             { package Horse;
               sub sound { "neigh" }
               sub speak {
                 my $class = shift;
                 print "a $class goes ", $class->sound, "!\n"
               }
             }
    
         Only the name of the package and the specific sound change.
         So can we somehow share the definition for `speak' between
         the Cow and the Horse?  Yes, with inheritance!
    
         Inheriting the windpipes
    
         We'll define a common subroutine package called `Animal',
         with the definition for `speak':
    
    
    
             { package Animal;
               sub speak {
                 my $class = shift;
                 print "a $class goes ", $class->sound, "!\n"
               }
             }
    
         Then, for each animal, we say it "inherits" from `Animal',
         along with the animal-specific sound:
    
             { package Cow;
               @ISA = qw(Animal);
               sub sound { "moooo" }
             }
    
         Note the added `@ISA' array.  We'll get to that in a minute.
    
         But what happens when we invoke `Cow->speak' now?
    
         First, Perl constructs the argument list.  In this case,
         it's just `Cow'.  Then Perl looks for `Cow::speak'.  But
         that's not there, so Perl checks for the inheritance array
         `@Cow::ISA'.  It's there, and contains the single name
         `Animal'.
    
         Perl next checks for `speak' inside `Animal' instead, as in
         `Animal::speak'.  And that's found, so Perl invokes that
         subroutine with the already frozen argument list.
    
         Inside the `Animal::speak' subroutine, `$class' becomes
         `Cow' (the first argument).  So when we get to the step of
         invoking `$class->sound', it'll be looking for `Cow->sound',
         which gets it on the first try without looking at `@ISA'.
         Success!
    
         A few notes about @ISA
    
         This magical `@ISA' variable (pronounced "is a" not "ice-
         uh"), has declared that `Cow' "is a" `Animal'.  Note that
         it's an array, not a simple single value, because on rare
         occasions, it makes sense to have more than one parent class
         searched for the missing methods.
    
         If `Animal' also had an `@ISA', then we'd check there too.
         The search is recursive, depth-first, left-to-right in each
         `@ISA'.  Typically, each `@ISA' has only one element
         (multiple elements means multiple inheritance and multiple
         headaches), so we get a nice tree of inheritance.
    
         When we turn on `use strict', we'll get complaints on
         `@ISA', since it's not a variable containing an explicit
         package name, nor is it a lexical ("my") variable.  We can't
         make it a lexical variable though (it has to belong to the
         package to be found by the inheritance mechanism), so
         there's a couple of straightforward ways to handle that.
    
         The easiest is to just spell the package name out:
    
             @Cow::ISA = qw(Animal);
    
         Or allow it as an implicitly named package variable:
    
             package Cow;
             use vars qw(@ISA);
             @ISA = qw(Animal);
    
         If you're bringing in the class from outside, via an
         object-oriented module, you change:
    
             package Cow;
             use Animal;
             use vars qw(@ISA);
             @ISA = qw(Animal);
    
         into just:
    
             package Cow;
             use base qw(Animal);
    
         And that's pretty darn compact.
    
         Overriding the methods
    
         Let's add a mouse, which can barely be heard:
    
             # Animal package from before
             { package Mouse;
               @ISA = qw(Animal);
               sub sound { "squeak" }
               sub speak {
                 my $class = shift;
                 print "a $class goes ", $class->sound, "!\n";
                 print "[but you can barely hear it!]\n";
               }
             }
    
             Mouse->speak;
    
         which results in:
    
             a Mouse goes squeak!
             [but you can barely hear it!]
    
         Here, `Mouse' has its own speaking routine, so
         `Mouse->speak' doesn't immediately invoke `Animal->speak'.
         This is known as "overriding".  In fact, we didn't even need
         to say that a `Mouse' was an `Animal' at all, since all of
         the methods needed for `speak' are completely defined with
         `Mouse'.
    
         But we've now duplicated some of the code from
         `Animal->speak', and this can once again be a maintenance
         headache.  So, can we avoid that?  Can we say somehow that a
         `Mouse' does everything any other `Animal' does, but add in
         the extra comment?  Sure!
    
         First, we can invoke the `Animal::speak' method directly:
    
             # Animal package from before
             { package Mouse;
               @ISA = qw(Animal);
               sub sound { "squeak" }
               sub speak {
                 my $class = shift;
                 Animal::speak($class);
                 print "[but you can barely hear it!]\n";
               }
             }
    
         Note that we have to include the `$class' parameter (almost
         surely the value of `"Mouse"') as the first parameter to
         `Animal::speak', since we've stopped using the method arrow.
         Why did we stop?  Well, if we invoke `Animal->speak' there,
         the first parameter to the method will be `"Animal"' not
         `"Mouse"', and when time comes for it to call for the
         `sound', it won't have the right class to come back to this
         package.
    
         Invoking `Animal::speak' directly is a mess, however.  What
         if `Animal::speak' didn't exist before, and was being
         inherited from a class mentioned in `@Animal::ISA'?  Because
         we are no longer using the method arrow, we get one and only
         one chance to hit the right subroutine.
    
         Also note that the `Animal' classname is now hardwired into
         the subroutine selection.  This is a mess if someone
         maintains the code, changing `@ISA' for <Mouse> and didn't
         notice `Animal' there in `speak'.  So, this is probably not
         the right way to go.
    
         Starting the search from a different place
    
         A better solution is to tell Perl to search from a higher
         place in the inheritance chain:
    
    
             # same Animal as before
             { package Mouse;
               # same @ISA, &sound as before
               sub speak {
                 my $class = shift;
                 $class->Animal::speak;
                 print "[but you can barely hear it!]\n";
               }
             }
    
         Ahh.  This works.  Using this syntax, we start with `Animal'
         to find `speak', and use all of `Animal''s inheritance chain
         if not found immediately.  And yet the first parameter will
         be `$class', so the found `speak' method will get `Mouse' as
         its first entry, and eventually work its way back to
         `Mouse::sound' for the details.
    
         But this isn't the best solution.  We still have to keep the
         `@ISA' and the initial search package coordinated.  Worse,
         if `Mouse' had multiple entries in `@ISA', we wouldn't
         necessarily know which one had actually defined `speak'.
         So, is there an even better way?
    
         The SUPER way of doing things
    
         By changing the `Animal' class to the `SUPER' class in that
         invocation, we get a search of all of our super classes
         (classes listed in `@ISA') automatically:
    
             # same Animal as before
             { package Mouse;
               # same @ISA, &sound as before
               sub speak {
                 my $class = shift;
                 $class->SUPER::speak;
                 print "[but you can barely hear it!]\n";
               }
             }
    
         So, `SUPER::speak' means look in the current package's
         `@ISA' for `speak', invoking the first one found.
    
         Where we're at so far...
    
         So far, we've seen the method arrow syntax:
    
           Class->method(@args);
    
         or the equivalent:
    
           $a = "Class";
           $a->method(@args);
    
         which constructs an argument list of:
    
           ("Class", @args)
    
         and attempts to invoke
    
           Class::method("Class", @Args);
    
         However, if `Class::method' is not found, then `@Class::ISA'
         is examined (recursively) to locate a package that does
         indeed contain `method', and that subroutine is invoked
         instead.
    
         Using this simple syntax, we have class methods, (multiple)
         inheritance, overriding, and extending.  Using just what
         we've seen so far, we've been able to factor out common
         code, and provide a nice way to reuse implementations with
         variations.  This is at the core of what objects provide,
         but objects also provide instance data, which we haven't
         even begun to cover.
    
         A horse is a horse, of course of course -- or is it?
    
         Let's start with the code for the `Animal' class and the
         `Horse' class:
    
           { package Animal;
             sub speak {
               my $class = shift;
               print "a $class goes ", $class->sound, "!\n"
             }
           }
           { package Horse;
             @ISA = qw(Animal);
             sub sound { "neigh" }
           }
    
         This lets us invoke `Horse->speak' to ripple upward to
         `Animal::speak', calling back to `Horse::sound' to get the
         specific sound, and the output of:
    
           a Horse goes neigh!
    
         But all of our Horse objects would have to be absolutely
         identical.  If I add a subroutine, all horses automatically
         share it.  That's great for making horses the same, but how
         do we capture the distinctions about an individual horse?
         For example, suppose I want to give my first horse a name.
         There's got to be a way to keep its name separate from the
         other horses.
    
    
         We can do that by drawing a new distinction, called an
         "instance".  An "instance" is generally created by a class.
         In Perl, any reference can be an instance, so let's start
         with the simplest reference that can hold a horse's name: a
         scalar reference.
    
           my $name = "Mr. Ed";
           my $talking = \$name;
    
         So now `$talking' is a reference to what will be the
         instance-specific data (the name).  The final step in
         turning this into a real instance is with a special operator
         called `bless':
    
           bless $talking, Horse;
    
         This operator stores information about the package named
         `Horse' into the thing pointed at by the reference.  At this
         point, we say `$talking' is an instance of `Horse'.  That
         is, it's a specific horse.  The reference is otherwise
         unchanged, and can still be used with traditional
         dereferencing operators.
    
         Invoking an instance method
    
         The method arrow can be used on instances, as well as names
         of packages (classes).  So, let's get the sound that
         `$talking' makes:
    
           my $noise = $talking->sound;
    
         To invoke `sound', Perl first notes that `$talking' is a
         blessed reference (and thus an instance).  It then
         constructs an argument list, in this case from just
         `($talking)'.  (Later we'll see that arguments will take
         their place following the instance variable, just like with
         classes.)
    
         Now for the fun part: Perl takes the class in which the
         instance was blessed, in this case `Horse', and uses that to
         locate the subroutine to invoke the method.  In this case,
         `Horse::sound' is found directly (without using
         inheritance), yielding the final subroutine invocation:
    
           Horse::sound($talking)
    
         Note that the first parameter here is still the instance,
         not the name of the class as before.  We'll get `neigh' as
         the return value, and that'll end up as the `$noise'
         variable above.
    
    
         If Horse::sound had not been found, we'd be wandering up the
         `@Horse::ISA' list to try to find the method in one of the
         superclasses, just as for a class method.  The only
         difference between a class method and an instance method is
         whether the first parameter is an instance (a blessed
         reference) or a class name (a string).
    
         Accessing the instance data
    
         Because we get the instance as the first parameter, we can
         now access the instance-specific data.  In this case, let's
         add a way to get at the name:
    
           { package Horse;
             @ISA = qw(Animal);
             sub sound { "neigh" }
             sub name {
               my $self = shift;
               $$self;
             }
           }
    
         Now we call for the name:
    
           print $talking->name, " says ", $talking->sound, "\n";
    
         Inside `Horse::name', the `@_' array contains just
         `$talking', which the `shift' stores into `$self'.  (It's
         traditional to shift the first parameter off into a variable
         named `$self' for instance methods, so stay with that unless
         you have strong reasons otherwise.)  Then, `$self' gets de-
         referenced as a scalar ref, yielding `Mr. Ed', and we're
         done with that.  The result is:
    
           Mr. Ed says neigh.
    
    
         How to build a horse
    
         Of course, if we constructed all of our horses by hand, we'd
         most likely make mistakes from time to time.  We're also
         violating one of the properties of object-oriented
         programming, in that the "inside guts" of a Horse are
         visible.  That's good if you're a veterinarian, but not if
         you just like to own horses.  So, let's let the Horse class
         build a new horse:
    
    
    
           { package Horse;
             @ISA = qw(Animal);
             sub sound { "neigh" }
             sub name {
               my $self = shift;
               $$self;
             }
             sub named {
               my $class = shift;
               my $name = shift;
               bless \$name, $class;
             }
           }
    
         Now with the new `named' method, we can build a horse:
    
           my $talking = Horse->named("Mr. Ed");
    
         Notice we're back to a class method, so the two arguments to
         `Horse::named' are `Horse' and `Mr. Ed'.  The `bless'
         operator not only blesses `$name', it also returns the
         reference to `$name', so that's fine as a return value.  And
         that's how to build a horse.
    
         We've called the constructor `named' here, so that it
         quickly denotes the constructor's argument as the name for
         this particular `Horse'.  You can use different constructors
         with different names for different ways of "giving birth" to
         the object (like maybe recording its pedigree or date of
         birth).  However, you'll find that most people coming to
         Perl from more limited languages use a single constructor
         named `new', with various ways of interpreting the arguments
         to `new'.  Either style is fine, as long as you document
         your particular way of giving birth to an object.  (And you
         were going to do that, right?)
    
         Inheriting the constructor
    
         But was there anything specific to `Horse' in that method?
         No.  Therefore, it's also the same recipe for building
         anything else that inherited from `Animal', so let's put it
         there:
    
    
    
           { package Animal;
             sub speak {
               my $class = shift;
               print "a $class goes ", $class->sound, "!\n"
             }
             sub name {
               my $self = shift;
               $$self;
             }
             sub named {
               my $class = shift;
               my $name = shift;
               bless \$name, $class;
             }
           }
           { package Horse;
             @ISA = qw(Animal);
             sub sound { "neigh" }
           }
    
         Ahh, but what happens if we invoke `speak' on an instance?
    
           my $talking = Horse->named("Mr. Ed");
           $talking->speak;
    
         We get a debugging value:
    
           a Horse=SCALAR(0xaca42ac) goes neigh!
    
         Why?  Because the `Animal::speak' routine is expecting a
         classname as its first parameter, not an instance.  When the
         instance is passed in, we'll end up using a blessed scalar
         reference as a string, and that shows up as we saw it just
         now.
    
         Making a method work with either classes or instances
    
         All we need is for a method to detect if it is being called
         on a class or called on an instance.  The most
         straightforward way is with the `ref' operator.  This
         returns a string (the classname) when used on a blessed
         reference, and `undef' when used on a string (like a
         classname).  Let's modify the `name' method first to notice
         the change:
    
           sub name {
             my $either = shift;
             ref $either
               ? $$either # it's an instance, return name
               : "an unnamed $either"; # it's a class, return generic
           }
    
         Here, the `?:' operator comes in handy to select either the
         dereference or a derived string.  Now we can use this with
         either an instance or a class.  Note that I've changed the
         first parameter holder to `$either' to show that this is
         intended:
    
           my $talking = Horse->named("Mr. Ed");
           print Horse->name, "\n"; # prints "an unnamed Horse\n"
           print $talking->name, "\n"; # prints "Mr Ed.\n"
    
         and now we'll fix `speak' to use this:
    
           sub speak {
             my $either = shift;
             print $either->name, " goes ", $either->sound, "\n";
           }
    
         And since `sound' already worked with either a class or an
         instance, we're done!
    
         Adding parameters to a method
    
         Let's train our animals to eat:
    
    
    
           { package Animal;
             sub named {
               my $class = shift;
               my $name = shift;
               bless \$name, $class;
             }
             sub name {
               my $either = shift;
               ref $either
                 ? $$either # it's an instance, return name
                 : "an unnamed $either"; # it's a class, return generic
             }
             sub speak {
               my $either = shift;
               print $either->name, " goes ", $either->sound, "\n";
             }
             sub eat {
               my $either = shift;
               my $food = shift;
               print $either->name, " eats $food.\n";
             }
           }
           { package Horse;
             @ISA = qw(Animal);
             sub sound { "neigh" }
           }
           { package Sheep;
             @ISA = qw(Animal);
             sub sound { "baaaah" }
           }
    
         And now try it out:
    
           my $talking = Horse->named("Mr. Ed");
           $talking->eat("hay");
           Sheep->eat("grass");
    
         which prints:
    
           Mr. Ed eats hay.
           an unnamed Sheep eats grass.
    
         An instance method with parameters gets invoked with the
         instance, and then the list of parameters.  So that first
         invocation is like:
    
           Animal::eat($talking, "hay");
    
    
    
         More interesting instances
    
         What if an instance needs more data?  Most interesting
         instances are made of many items, each of which can in turn
         be a reference or even another object.  The easiest way to
         store these is often in a hash.  The keys of the hash serve
         as the names of parts of the object (often called "instance
         variables" or "member variables"), and the corresponding
         values are, well, the values.
    
         But how do we turn the horse into a hash?  Recall that an
         object was any blessed reference.  We can just as easily
         make it a blessed hash reference as a blessed scalar
         reference, as long as everything that looks at the reference
         is changed accordingly.
    
         Let's make a sheep that has a name and a color:
    
           my $bad = bless { Name => "Evil", Color => "black" }, Sheep;
    
         so `$bad->{Name}' has `Evil', and `$bad->{Color}' has
         `black'.  But we want to make `$bad->name' access the name,
         and that's now messed up because it's expecting a scalar
         reference.  Not to worry, because that's pretty easy to fix
         up:
    
           ## in Animal
           sub name {
             my $either = shift;
             ref $either ?
               $either->{Name} :
               "an unnamed $either";
           }
    
         And of course `named' still builds a scalar sheep, so let's
         fix that as well:
    
           ## in Animal
           sub named {
             my $class = shift;
             my $name = shift;
             my $self = { Name => $name, Color => $class->default_color };
             bless $self, $class;
           }
    
         What's this `default_color'?  Well, if `named' has only the
         name, we still need to set a color, so we'll have a class-
         specific initial color.  For a sheep, we might define it as
         white:
    
           ## in Sheep
           sub default_color { "white" }
    
         And then to keep from having to define one for each
         additional class, we'll define a "backstop" method that
         serves as the "default default", directly in `Animal':
    
           ## in Animal
           sub default_color { "brown" }
    
         Now, because `name' and `named' were the only methods that
         referenced the "structure" of the object, the rest of the
         methods can remain the same, so `speak' still works as
         before.
    
         A horse of a different color
    
         But having all our horses be brown would be boring.  So
         let's add a method or two to get and set the color.
    
           ## in Animal
           sub color {
             $_[0]->{Color}
           }
           sub set_color {
             $_[0]->{Color} = $_[1];
           }
    
         Note the alternate way of accessing the arguments: `$_[0]'
         is used in-place, rather than with a `shift'.  (This saves
         us a bit of time for something that may be invoked
         frequently.)  And now we can fix that color for Mr. Ed:
    
           my $talking = Horse->named("Mr. Ed");
           $talking->set_color("black-and-white");
           print $talking->name, " is colored ", $talking->color, "\n";
    
         which results in:
    
           Mr. Ed is colored black-and-white
    
    
         Summary
    
         So, now we have class methods, constructors, instance
         methods, instance data, and even accessors.  But that's
         still just the beginning of what Perl has to offer.  We
         haven't even begun to talk about accessors that double as
         getters and setters, destructors, indirect object notation,
         subclasses that add instance data, per-class data,
         overloading, "isa" and "can" tests, `UNIVERSAL' class, and
         so on.  That's for the rest of the Perl documentation to
         cover.  Hopefully, this gets you started, though.
    
    
    
    

    SEE ALSO

         For more information, see the perlobj manpage (for all the
         gritty details about Perl objects, now that you've seen the
         basics), the perltoot manpage (the tutorial for those who
         already know objects), the perlbot manpage (for some more
         tricks), and books such as Damian Conway's excellent Object
         Oriented Perl.
    
    
    

    COPYRIGHT

         Copyright (c) 1999, 2000 by Randal L. Schwartz and
         Stonehenge Consulting Services, Inc.  Permission is hereby
         granted to distribute this document intact with the Perl
         distribution, and in accordance with the licenses of the
         Perl distribution; derived documents must include this
         copyright notice intact.
    
         Portions of this text have been derived from Perl Training
         materials originally appearing in the Packages, References,
         Objects, and Modules course taught by instructors for
         Stonehenge Consulting Services, Inc. and used with
         permission.
    
         Portions of this text have been derived from materials
         originally appearing in Linux Magazine and used with
         permission.
    
    
    
    


    Поиск по тексту MAN-ов: 




    Партнёры:
    PostgresPro
    Inferno Solutions
    Hosting by Hoster.ru
    Хостинг:

    Закладки на сайте
    Проследить за страницей
    Created 1996-2024 by Maxim Chirkov
    Добавить, Поддержать, Вебмастеру