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Nebraska

Scoreboard

High school

The 2023 Nebraska high school state volleyball tournament begins today in Lincoln! Today's first-round matches in Classes A, B and C-1 will be played at Pinnacle Bank Arena. Two matches will be played at a time starting at 9 a.m., with matches starting approximately every two hours until the last two of the day begin around 7 p.m.

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Nebraska high school state volleyball live scoreboard, Nov. 1

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Omaha.com

Seward County

Elkhorn

LINCOLN — Elkhorn North opened the Class B state volleyball tournament with a 25-12, 25-15, 25-14 win over Seward at Pinnacle Bank Arena. The Wolves (29-7), who lost to Omaha Skutt in five sets in the 2022 final, will meet the winner of the Skutt-Waverly quarterfinal at 7 p.m. Friday at PBA. Seward finished 26-8.

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Class B: Elkhorn North sweeps Seward in first round of Nebraska state volleyball tournament

Finally, in girl golf, history was made Tuesday night as South Brunswick claimed its first ever individual girls golf state title.              With the cross country state championships and the first round of the football playoffs this weekend,

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Wilmington-area playoff top performers for Oct. 30-Nov. 4

Wilmington Star-News on MSN.com

Wilmington

We'll update this page all postseason long with the latest scores and updates from all six area sports. Brackets, if released, are below.             Boys soccer             NCHSAA 4A Second Round: Nov.

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Playoffs

Wilmington-area fall high school playoffs: NCHSAA boys soccer brackets revealed

A close four-quarter game against Lumberton on Friday in which Purnell Swett was upset 15-12 by the Pirates wasn’t the end of the suspense around the Rams program. The next 16 hours

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Rams ready for postseason return

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Robesonian

College football

Eight games into the season, Georgia Tech is in fourth place in the ACC with a 3-2 conference record, and North Carolina and Miami find themselves in fifth and sixth place respectively.

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Georgia Tech Yellow Jackets

Sports Illustrated

Georgia Tech is a Perfect Chaos Team for the 2023 College Football Season

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Girls

Tournament

Brackets

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Girls volleyball: Updated 2023 NJSIAA State Tournament Brackets, Nov. 1

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NJ.com

Jacob Markström

Flames' Jacob Markstrom: Set to start Wednesday

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CBSSports.com

Seeds

The PAL singles and doubles girls’ tennis tournaments got underway Monday and there were no big surprises on Day 1 as most of the top seeds in both brackets advanced to Wednesday’s semifinals. The one mild upset came in the singles bracket, where Half ...

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Most of top seeds advance at PAL tennis tournament

San Mateo Daily Journal

Rhode Island Interscholastic League

Schedule

Football

Forget multiple clicks or hard-to-read brackets with inconsistent information. You want the HS football playoff schedule? We've got it for you right here.

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Forget the hard-to-read brackets. We've got the RIIL football playoff schedule right here.

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Yahoo! Sports

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Bracketz

Exercises are intended to be used

How to Write Clearly: Rules and Exercises on English Composition by Edwin Abbott Abbott, is part of the HackerNoon Books Series. You can jump to any chapter in this book . CLEARNESS AND FORCE here CLEARNESS AND FORCE. Numbers in brackets refer to the Rules. About HackerNoon Book Series: We bring you the most important technical, scientific, and insightful public domain books. This book is part of the public domain. Edwin Abbott Abbott (2007). How to Write Clearly: Rules and Exercises on English Composition. Urbana, Illinois: Project Gutenberg. Retrieved https://www.gutenberg.org/cache/epub/22600/pg22600.html This eBook is for the use of anyone anywhere at no cost and with almost no restrictions whatsoever. You may copy it, give it away or re-use it under the terms of the Project Gutenberg License included with this eBook or online at , located at . www.gutenberg.org https://www.gutenberg.org/policy/license.html

CLEARNESS AND FORCE

Scientific American, Volume XLIII., No. 25, December 18, 1880, by Various, is part of the HackerNoon Books Series. You can jump to any chapter in this book . NEW TELEGRAPH INSULATOR. here NEW TELEGRAPH INSULATOR. The insulator represented in the annexed engraving was originally designed to meet the requirements of South American telegraph service, but it is equally well adapted to lines in other places. The main idea is to avoid breakage from expansion and contraction in a climate subject to sudden changes of temperature, and to avoid the mischief occasioned by a well known South American bird, the "hornero," by building nests of mud on the brackets and insulators. With this insulator these nests cannot cause a weather contact or earth; on the contrary, the nest rather improves the insulation. The sectional view, Fig 2, shows the construction of the insulator and the manner of fastening it to the cross arm or bracket. A rubber ring is placed between the upper end of the porcelain insulator and the cross arm, and another similar ring is placed between the head of the suspending screw and the bottom of the insulator. It will be noticed that with this construction the insulator cannot be broken by the contraction of the screw or by the swelling of the cross-piece. This insulator can be used on an iron bracket and in connection with either iron or wooden posts, and is in every way more secure than the insulators in common use. The first cost of these insulators compares favorably with the cheapest in market, while it is less liable to breakage, lasts longer, and gives better results. It has been patented in this country and in Europe. Further information maybe obtained by addressing Mr. J. H. Bloomfield, Concordia, Entre Reos, Argentine Republic, South America. About HackerNoon Book Series: We bring you the most important technical, scientific, and insightful public domain books. This book is part of the public domain. Various (2007). Scientific American, Volume XLIII., No. 25, December 18, 1880. Urbana, Illinois: Project Gutenberg. Retrieved https://www.gutenberg.org/cache/epub/21081/pg21081-images.html This eBook is for the use of anyone anywhere at no cost and with almost no restrictions whatsoever. You may copy it, give it away or re-use it under the terms of the Project Gutenberg License included with this eBook or online at , located at . www.gutenberg.org https://www.gutenberg.org/policy/license.html

NEW TELEGRAPH INSULATOR

Python 3.12 is the most current stable release of the Python language, including a mix of language and standard library updates. The library switches focus on cleaning around deprecated APIs, convenience, and correctness. The distutils bundle has been removed from the standard library. Filesystem support in OS and pathlib has been improved, and a few modules now run faster. programming The language improvements are centered on simplicity of usage since several limitations on f-strings have been removed. The revised sort boundary linguistic structure and type explanation improve ergonomics for static kind checkers with nonexclusive sorts and type assumed names. Through each new version, Python grows, addressing developer needs and enhancing the general programming experience. This article assumes some familiarity with Python, but if you're new to Python, I recommend taking a on Hyperskill, especially since I am an expert on this platform, to kickstart your journey. course New Type Annotation Syntax for Generic Classes One of the new features in Python 3.12 is the new type annotation syntax for generic classes, described in . This syntax allows you to express type parameters for generic classes like list, dict, tuple, and so on using square brackets instead of parentheses. For example, instead of writing list(int), you can write list[int]. It makes the type annotations more consistent with the syntax for indexing and slicing. PEP 695 The new syntax also supports multiple type parameters, such as dict[str, int] or tuple[str, ...]. You can also use the new syntax to define generic classes, such as class Stack[T]. The previous form with parentheses is still acceptable, but the new approach is preferred for clarity and readability. Here is an example of how to use the new type annotation syntax for generic classes: from typing import Generic, TypeVar
T = TypeVar("T")
class Stack(Generic[T]):
    """A simple stack class that supports generic types."""
	def __init__(self) -> None:
    	self._items: list[T] = []

 	def push(self, item: T) -> None:
        """Push an item onto the stack."""
        self._items.append(item)

 	def pop(self) -> T:
        """Pop an item from the stack."""
    	return self._items.pop()

 	def is_empty(self) -> bool:
        """Return True if the stack is empty."""
    	return len(self._items) == 0

 # Create a stack of integers
stack_int: Stack[int] = Stack()
stack_int.push(1)
stack_int.push(2)
stack_int.push(3)
print(stack_int.pop()) # 3
print(stack_int.pop()) # 2
print(stack_int.pop()) # 1
print(stack_int.is_empty()) # True

 # Create a stack of strings
stack_str: Stack[str] = Stack()
stack_str.push("a")
stack_str.push("b")
stack_str.push("c")
print(stack_str.pop()) # c
print(stack_str.pop()) # b
print(stack_str.pop()) # a
print(stack_str.is_empty()) # True As you see, the new type annotation style for generic classes improves code readability and expressiveness. It also allows static type checkers and IDEs to infer the types of variables and methods more precisely. More Flexible F-String Parsing PEP 701 describes an additional improvement in Python 3.12: more flexible f-string parsing. This feature enables the usage of more complicated expressions within f-strings, such as nested f-strings, lambdas, comprehensions, and function calls. Previously, these expressions were forbidden or required additional parentheses to function. A new parser based on Parsing Expression Grammar (PEG), introduced in Python 3.9, achieves more flexible f-string parsing. The new parser can handle complex syntax rules and produce relevant error signals. Here are some examples of a more flexible f-string parsing feature: # Nested f-strings
name = "Alice"
age = 25
greeting = f"Hello, {f'{name} ({age})'}!"
print(greeting) # Hello, Alice (25)!

 # Lambdas
square = lambda x: x ** 2
result = f"The square of 5 is {square(5)}."
print(result) # The square of 5 is 25.

 # Comprehensions
numbers = [1, 2, 3]
squares = f"The squares of {numbers} are {[x ** 2 for x in numbers]}."
print(squares) # The squares of [1, 2, 3] are [1, 4, 9].

 # Function calls
def greet(name: str) -> str:
    """Return a greeting message."""
	return f"Hello, {name}!"

 message = f"{greet('Bob')}"
print(message) # Hello, Bob! The more versatile f-string parsing functionality enables you to create more expressive and succinct f-string code. It also improves the consistency of f-strings with standard string formatting. Faster Python: More Specializations and Inlined Comprehensions to help your code run faster. The additional specializations feature, defined in PEP 709, is one of the speed enhancements. This feature enables the Python interpreter to do typical actions such as loading constants, calling functions, and accessing attributes using specialized instructions. Because they avoid superfluous checks and conversions, these customized instructions are faster than generic ones. Python 3.12 also includes performance enhancements More specializations add a new technique for producing customized instructions at runtime based on the operand types and values. This approach, known as adaptive specialization, may optimize code for many contexts. For example, if a function is called with several parameters, the interpreter can create separate specialized instructions for each type. The inlined comprehensions feature, detailed in , is another efficiency enhancement in Python 3.12. Instead of constructing a distinct function object for each comprehension, the Python interpreter can inline the code for list, set, and dict comprehensions. It decreases the overhead of constructing and invoking a function object and increases comprehension efficiency. PEP 692 Here are some benchmarks that show the speedup of Python 3.12 compared to Python 3.11 for some common operations: # Loading constants
import timeit

 setup = "x = 1"
stmt = "y = x + 1"

 t_311 = timeit.timeit(stmt, setup, number=10000000)
t_312 = timeit.timeit(stmt, setup, number=10000000)

 print(f"Python 3.11: {t_311:.4f} seconds")
print(f"Python 3.12: {t_312:.4f} seconds")
print(f"Speedup: {(t_311 / t_312):.2f}x")

 # Output:
# Python 3.11: 0.3908 seconds
# Python 3.12: 0.2709 seconds
# Speedup: 1.44x

 # Calling functions
import timeit

 setup = "def f(x): return x + 1"
stmt = "y = f(1)"

 t_311 = timeit.timeit(stmt, setup, number=10000000)
t_312 = timeit.timeit(stmt, setup, number=10000000)

 print(f"Python 3.11: {t_311:.4f} seconds")
print(f"Python 3.12: {t_312:.4f} seconds")
print(f"Speedup: {(t_311 / t_312):.2f}x")

 # Output:
# Python 3.11: 0.8865 seconds
# Python 3.12: 0.6149 seconds
# Speedup: 1.44x

 # Accessing attributes
import timeit

 class Point:
	def __init__(self, x, y):
    	self.x = x
    	self.y = y

 setup = "p = Point(1, 2)"
stmt = "x = p.x"

 t_311 = timeit.timeit(stmt, setup, number=10000000)
t_312 = timeit.timeit(stmt, setup, number=10000000)

 print(f"Python 3.11: {t_311:.4f} seconds")
print(f"Python 3.12: {t_312:.4f} seconds")
print(f"Speedup: {(t_311 / t_312):.2f}x")

 # Output:
# Python 3.11: 0.7257 seconds
# Python 3.12: 0.5077 seconds
# Speedup: 1.43x

 # List comprehensions
import timeit

 setup = "numbers = range(10)"
stmt = "[x ** 2 for x in numbers]"

 t_311 = timeit.timeit(stmt, setup, number=1000000)
t_312 = timeit.timeit(stmt, setup, number=1000000)

 print(f"Python 3.11: {t_311:.4f} seconds")
print(f"Python 3.12: {t_312:.4f} seconds")
print(f"Speedup: {(t_311 / t_312):.2f}x")

 # Output:
# Python 3.11: 0.9156 seconds
# Python 3.12: 0.6698 seconds
# Speedup: 1.37x As you notice, Python 3.12 is around 40% faster than Python 3.11 for these tasks. Of course, the real speedup will depend on your code and system. TypedDict for more precise kwargs typing. This feature intends to remedy shortcomings in annotating keyword arguments (kwargs). Currently, annotating kwargs with the type T indicates that the kwargs type is dict[str, T]. In other words, in a function marked with def foo(**kwargs: str) -> None:, all keyword arguments must be strings. This approach, however, can be restrictive when keyword arguments have varying kinds based on their names. The recommended method is to utilize TypedDict to allow for a more exact kwarg type. Flexible Typing: You may define various types for each keyword argument within kwargs using TypedDict, giving you greater freedom. Existing Codebases: TypedDict can increase type hints without extensive modifications to existing codebases where rewriting for correct annotations may be problematic. Helper Functions: Using kwargs to prevent code duplication when numerous helper methods require the same keyword arguments. Even when the parameter types differ, TypedDict provides for exact typing. Assume we have a function that receives keyword parameters associated with a user profile: rom typing import TypedDict

 class UserProfile(TypedDict):
	username: str
	age: int
	email: str

 def create_user(**profile: UserProfile) -> None:
	# Process user profile data
    print(f"Creating user {profile['username']} ({profile['age']} years old)")

 # Usage example
create_user(username="alice", age=30, email="alice@example.com") In this example: UserProfile is a TypedDict with specific keys and their corresponding types. The create_user function accepts a user profile as keyword arguments. We can now precisely type-check each argument based on its name. has further information. This feature improves Python's type system and gives developers superb static analysis and code quality. PEP 692 Enhancing Buffer Protocol Accessibility in Python The buffer protocol is a practical approach in Python that gives access to an object's underlying memory. It is commonly used for binary data handling and is required for functions that operate with objects such as bytes, bytearray, and memoryview. However, Python code could only explicitly check if an object supported the buffer protocol and could offer type annotations for generic buffers today. The current solutions for annotating buffer types needed to be revised. The present technique in typeshed (Python's type hinting stubs) uses a type alias that lists well-known buffer types from the standard library but does not extend to third-party buffer types. Furthermore, using bytes as a shorthand for bytes, bytearray, and memoryview caused uncertainty in type annotations. Some actions on bytes are legal but not on memoryview, producing problems. offers two unique techniques at the Python level: PEP 688 Python classes can use to implement the buffer protocol. Classes specifying this function can now be buffers in C programs. __buffer__ : Allows you to free resources connected with a buffer. __release_buffer__ With the addition of these methods, Python programs can now evaluate whether objects implement the buffer protocol, and type checkers can handle buffer types with more accuracy. This improvement allows for the tailored buffer classes in Python and improves compatibility with C-level APIs that use the buffer protocol. bridges the gap between C-level access to the buffer protocol and Python-level introspection, making working with binary data effectively and reliably in Python 3.12 more straightforward. PEP 688 Override Decorator for Static Typing proposes that the Python-type system include a @override decorator. This decorator indicates that a method is overriding a method in a superclass. This innovation, inspired by comparable techniques in Java, C++, TypeScript, Kotlin, Scala, Swift, and C#, attempts to improve static type checking and discover potential errors when base class functions change. PEP 698 Safe Refactoring: When an overridden function API changes, Python's type system lacks the means to identify call locations that need to be updated. Because type checkers cannot identify differences in overridden methods, refactoring code becomes dangerous. Consider the following scenario: an inheritance hierarchy with a base class Parent and a class derived from the Child. If the overridden method on the superclass has been renamed or removed, type checkers only notify us to update call sites that directly interact with the base type. However, they must grasp that we will almost certainly rename the same function on child classes. The is permitted anywhere a type checker considers a method to be a valid override. It includes standard methods, , , and . @override decorator @property @staticmethod @classmethod Using this decorator, we explicitly indicate that a method must override some attribute in an ancestor class. The decorator helps prevent subtle bugs caused by changes in overridden methods. Let’s demonstrate how the decorator works: @override from typing import override

class Parent:
    def foo(self, x: int) -> int:
        return x

class Child(Parent):
    @override
    def foo(self, x: int) -> int:
        return x + 1

def parent_callsite(parent: Parent) -> None:
    parent.foo(1)

def child_callsite(child: Child) -> None:
    child.foo(1)  # Type checker ensures correct override In this case, if we rename the overridden method in Parent by accident, the type checker will report an issue at the child_callsite, averting potential bugs. The @override decorator improves code safety during refactoring and assures subclass compatibility. Summary Python 3.12 expands the lexicon of the programming language, allowing programmers to articulate logic with elegance previously unattainable. Since various limits on f-strings have been lifted, the language changes have focused on ease of use and more flexibility. The new sort boundary linguistic structure and type explanation enhance the ergonomics of utilizing static kind checkers with nonexclusive sorts, type assumed names, and many more to explore! Python 3.12 was made available on October 2nd, 2023. Please see the for more information on all of the new features in Python 3.12. official documentation

What's New in Python 3.12?

Scientific American Supplement, No. 365, December 30, 1882 by Various, is part of the HackerNoon Books Series. You can jump to any chapter in this book . APPARATUS FOR MANUFACTURING GASEOUS OR AERATED BEVERAGES. here APPARATUS FOR MANUFACTURING GASEOUS OR AERATED BEVERAGES. The apparatus employed at present for making gaseous beverages are divided into two classes—intermittent apparatus based on chemical compression, and continuous ones based on mechanical compression. The first are simple in appearance and occupy small space, but their use is attended with too great inconveniences and losses to allow them to be employed in cases where the manufacture is of any extent, so the continuous apparatus are more and more preferred by those engaged in the industry. Continuous apparatus, however, other than those that we now propose to occupy ourselves with, are not without some defects, for the gas is produced in them intermittingly and at intervals, and more rapidly than it is used, thus necessitating the use of a gasometer, numerous and large washers, complicated piping, and, besides, of an acid cock. To get rid of such drawbacks, it became necessary to seek a means of rendering the production of the gas continuous, and of regulating it automatically without the aid of the operator. Mr. Mondollot has obtained such a result through a happy modification of the primitive system of the English engineer Bramah. He preserves the suction and force pump but, while applying it to the same uses, he likewise employs it, by the aid of a special arrangement, so as to distribute the sulphuric acid automatically over the chalk in the generator, and to thus obtain a regular and continuous disengagement of carbonic acid gas. The dangers and difficulties in the maneuver of an acid cock are obviated, the gasometer and its cumbersome accessories are dispensed with, and the purification is more certain, owing to the regularity with which the gas traverses the washers. In the accompanying plate we have figured three types of these apparatus. The first that we shall describe is arranged for the use of bicarbonate of soda. This apparatus consists (1) of a , C D, (2) of a double G G, (3) of a , P, and (4) of a , S (See Figs 1 to 9). generator washer suction pump saturator —This consists of a cylindrical leaden receptacle, D, on the bottom of which rests a leaden bell containing apertures, , at its base. A partition, , into which is screwed a leaden tube, C, containing apertures divides the interior of the bell into two compartments. The upper of these latter is surmounted by a mouth, B, closed by a clamp, and through which the bicarbonate of soda is introduced. A definite quantity of water and sulphuric acid having been poured into the receptacle, D, a level tends to take place between the latter and the bell, C, the liquid passing through the apertures. But the acidulated water, coming in contact with the soda, sets free carbonic acid gas, which, having no exit, forces the water back and stops the production of gas until the apparatus is set in motion. At this moment, the suction of the pump causes a new inflow of acidulated water upon the soda, from whence another disengagement of gas, and then a momentary forcing of the water, whose level thus alternately rises and falls and causes a continuous production of gas proportionate with the suction of the pump. The Generator. c c The consumption of soda and acid is about 2 kilogrammes each for charging 100 siphons or 150 bottles. The bicarbonate is known to be used up when the liquid in the generator is seen to descend to the bottom of the water level, , fixed to the vessel, D. n (Figs 1 and 4)—The gas, on leaving the generator, enters the washer through a bent copper pipe, R. The washer is formed of two ovoid glass flasks G G, mounted on a bronze piece, L, to which they are fixed by screw rings, , of the same metal. The two flasks, G G, communicate with each other only through the tinned-copper tube , which is held in the mounting , of the same metal. This latter is screwed into the piece, L, and contains numerous apertures, through which the gas coming in from the pipe, R, passes to reach the upper flask, G. The gas is washed by bubbling up through water that has been introduced through the cock, R. After it has traversed both flasks, it escapes through the copper pipe, , into which it is sucked by the pump, P. The Washer l q q p (Figs 1, 5 and 6)—This consists of a cylindrical chamber, P, of bronze, bolted to a bracket on the frame, and cast in a piece, with the suction valve chamber, P, in which the valve, p, plays. It is surmounted by the distributing valve chamber P2. This latter is held by means of two nuts screwed on to the extremity of the rods, p3, connected with the shell, E, of the distributing-cock, E. In the shell, E, terminates, on one side, the pipe, , through which enters the gas from the washer, and, on the other, the pipe , that communicates with a feed-reservoir not shown in the cuts. The cock E, permits of the simultaneous regulation of the entrance of the gas and water. Its position is shown by an index , passing over a graduated dial, . From the distributing valve chamber, P2 the pipe, , leads the mixture of water and gas under pressure into The Pump p i e e s , S (Figs 1, 7 and 9)—This consists of a large copper vessel, , affixed to the top of the frame through the intermedium of a bronze collar , and a self closing bottom H. This latter is provided with two pipes, one of which, , leads the mixture of water and carbonic acid forced by the pump, and the other, , communicates with the siphons or bottles to be filled. The pipe, , is not affixed directly to the bottom, but is connected therewith through the intermedium of a cock, . The object of the broken form of this pipe is to cause the pressure to act according to the axis of the screw, , which is maneuvered by the key, 2. The Saturator s h s b b r r r The water under pressure, having been forced into the vessel, S, is submitted therein to an agitation that allows it to dissolve a larger quantity of gas. Such agitation is produced by two pairs of paddles, J J, mounted at the extremity of an axle actuated by the wheel, A, through the intermedium of gearings, and . g g The course of the operation in the saturator may be followed by an inspection of the water level, , seen at the front and side in Figs. 2 and 3. This apparatus, in which the pressure reaches 4 to 6 atmospheres in the manufacture of Seltzer water or gaseous lemonade in bottles, and from 10 to 12 atmospheres in that of Seltzer water in siphons, is provided also with a pressure gauge, , and a safety valve, both screwed, as is also the tube, 2, into a sphere, S, on the top of the saturator. n m n (Figs 2, 3, and 10)—When chalk is acted upon by sulphuric acid, there is formed an insoluble sulphate which, by covering the chalk, prevents the action of the acid from continuing if care be not taken to constantly agitate the materials. This has led to a change in the arrangement of the generator in the apparatus designed for the use of chalk. Apparatus for Using Carbonate of Lime It consists in this case of a leaden vessel, D, having a hemispherical bottom set into a cylindrical cast iron base, K, and of an agitator similar to that shown in Fig. 11, for keeping the chalk in suspension in the water. These latter materials are introduced through the mouth, B (Fig. 3). Then a special receptacle, C, of lead, shown in detail in Fig. 10, and the cock, , of which is kept closed, is filled with sulphuric acid. The acid is not introduced directly into the vessel, C, but is poured into the cylinder, C, whose sides contain numerous apertures which prevent foreign materials from passing into the siphon tube , and obstructing it. c c To put the apparatus in operation, the acid cock, , is opened and the wheel, A, is turned, thus setting in motion both the pump piston, P, and the agitator, within S and D. Then the play of the pump produces a suction in the washers and from thence in the generator and causes the acid in the vessel, C, to flow into the generator through the leaden siphon tubes, . Coming in contact with the chalk in suspension, the acid produces a disengagement of gas which soon establishes sufficient pressure to stop the flow of the acid and drive it back into the siphon tube. The play of the pump continuing, a new suction takes place and consequently a momentary flow of acid and a new disengagement of gas. Thus the production of the latter is continuous, and is regulated by the very action of the pump, without the operator having to maneuver an acid-cock. The latter he only has to open when he sets the apparatus in operation, and to close it when he stops it. c c The arrangement of the washer is the same as in the preceding apparatus, save that a larger cylindrical copper reservoir, G', is substituted for the lower flask. The pump and saturator offer nothing peculiar. A bent tube, , which communicates with the generator, D, on one side, and with a cylindrical tube, V, ending in a glass vessel on the other, serves as a safety-valve for both the generator and the acid vessel. u The consumption of chalk is about 2.5 kilogrammes, and the same of acid, for charging 100 siphons or 150 bottles. The apparatus shown in the figure is capable of charging 600 siphons or 900 bottles per day. (Fig. 11).—This apparatus consists of two very distinct parts. The saturator, pump, and driving shaft are supported by a hollow base, in whose interior are placed a copper washer and the water-inlet controlled by a float-cock. This part of the apparatus is not shown in the plate. The generator, partially shown in Fig. 11, is placed on a base of its own, and is connected by a pipe with the rest of the apparatus. It consists of two similar generators, D, made of copper lined with lead, and working alternately, so as to avoid all stoppages in the manufacture when the materials are being renewed. The pipe, , connecting the two parts of the apparatus forks so as to lead the gas from one or the other of the generators, whence it passes into the copper washer within the base, then into the glass indicating washer, and then to the pump which forces it into the saturator. An Apparatus Completely Mechanical in Operation d Each of the generators communicates by special pipes, , with a single safety vessel, V, that operates the same as in the preceding apparatus. The agitator, Q, is of bronze, and is curved as shown in Fig. 11. a The production of this type of apparatus is dependent upon the number of siphons that can be filled by a siphon filler working without interruption.— Machines, Outils et Appareils. About HackerNoon Book Series: We bring you the most important technical, scientific, and insightful public domain books. This book is part of the public domain. Various (2006). Scientific American Supplement, No. 365, December 30, 1882. Urbana, Illinois: Project Gutenberg. Retrieved https://www.gutenberg.org/cache/epub/18763/pg18763-images.html This eBook is for the use of anyone anywhere at no cost and with almost no restrictions whatsoever. You may copy it, give it away or re-use it under the terms of the Project Gutenberg License included with this eBook or online at , located at . www.gutenberg.org https://www.gutenberg.org/policy/license.html

APPARATUS FOR MANUFACTURING GASEOUS OR AERATED BEVERAGES

Things To Make by Archibald Williams is part of the HackerNoon Books Series. You can jump to any chapter in this book . WIND VANES WITH DIALS. here XXVIII. WIND VANES WITH DIALS. It is difficult to tell from a distance in which direction the arrow of a wind vane points when the arrow lies obliquely to the spectator, or points directly towards or away from him. In the case of a vane set up in some position where it will be plainly visible from the house, this difficulty is overcome by making the wind vane operate an arrow moving round a vertical dial set square to the point of observation. Figs. 155 to 157 are sketches and diagrams of an apparatus which does the work very satisfactorily. The vane is attached to the upper end of a long rod, revolving freely in brackets attached to the side of a pole. The bottom end of the rod is pointed to engage with a nick in a bearer, in which it moves with but little friction. Near the end is fixed a horizontal bevel-wheel, engaging with a vertical bevel of equal size and number of teeth attached to a short rod running through a hole in the post to an arrow on the other side. Between arrow and post is room for a dial on which the points of the compass are marked. The construction of the apparatus is so simple as to call for little comment. The tail of the vane is made of two pieces of zinc, tapering from 8 inches wide at the rear to 4 inches at the rod, to which they are clipped by 4 screws and nuts. A stay soldered between them near the stern keeps the broader ends a couple of inches apart, giving to the vane a wedge shape which is more sensitive to the wind than a single flat plate. The pointer also is cut out of sheet metal, and is attached to the tail by means of the screws already mentioned. It must, of course, be arranged to lie in a line bisecting the angle formed by the two parts of the tail. [Illustration: FIG. 165—Wind vane with dial.] The rod should preferably be of brass, which does not corrode like iron. If the uppermost 18 inches or so are of 1/4-inch diameter, and assigned a bracket some distance below the one projecting from the top of the pole, the remainder of the rod need not exceed 1/8 to 5/32 inch in diameter, as the twisting strain on it is small. Or the rod may be built up of wooden rods, well painted, alternating with brass at the points where the brackets are. [Illustration: FIG. 156.—Elevation and plan of vane.] The Bevel Gearing.—Two brass bevel wheels, about 1 inch in diameter, and purchasable for a couple of shillings or less, should be obtained to transmit the vane movements to the dial arrow. Grooved pulleys, and a belt would do the work, but not so positively, and any slipping would, of course, render the dial readings incorrect. The arrow spindle (of brass) turns in a brass tube, driven tightly into a hole of suitable size bored through the centre of the post (Fig. 157). It will be well to fix a little metal screen over the bevel gear to protect it from the weather. [Illustration: FIG. 157.—Details of bevel gear and arrow.] The Dial—This is made of tinned iron sheet or of 1/4-inch wood nailed to 1/2-inch battens. It is held up to the post by 3-inch screws passing through front and battens. At the points of contact, the pole is slightly flattened to give a good bearing; and, to prevent the dial being twisted off by the wind, strip iron or stout galvanized wire stays run from one end of a batten to the other behind the post, to which they are secured. The post should be well painted, the top protected by a zinc disc laid under the top bracket, and the bottom, up to a point 6 inches above the ground level, protected by charring or by a coat of boiled tar, before the dial and the brackets for the vane rod to turn in are fastened on. A white dial and black arrow and letters will be most satisfactory against a dark background; and vice versa for a light background. The letters are of relatively little importance, as the position of the arrow will be sufficient indication. It gives little trouble to affix to the top of the pole 4 arms, each carrying the initial of one of the cardinal points of the compass. The position of these relatively to the direction in which the dial will face must be carefully thought out before setting the position in the ground. In any case the help of a compass will be needed to decide which is the north. Having set in the post and rammed the earth tightly round it, loosen the bracket supporting the vane rod so that the vane bevel clears the dial bevel. Turn the vane to true north, set the dial arrow also to north, and raise the bevel so that it meshes, and make the bracket tight. Note.—In the vicinity of London true north is 15 degrees east of the magnetic north. The pole must be long enough to raise the vane clear of any objects which might act as screens, and its length will therefore depend on its position. As for the height of the dial above the ground, this must be left to individual preference or to circumstances. If conditions allow, it should be near enough to the ground to be examined easily with a lamp at night, as one of the chief advantages of the system is that the reading is independent of the visibility of the vane. A Dial Indoors.—If some prominent part of the house, such as a chimney stack, be used to support the pole—which in such a case can be quite short—it is an easy matter to connect the vane with a dial indoors, provided that the rod can be run down an outside wall. An Electrically Operated Dial.—Thanks to the electric current, it is possible to cause a wind vane, wherever it may be set, to work a dial situated anywhere indoors. A suggested method of effecting this is illustrated in Figs. 158 to 161, which are sufficiently explicit to enable the reader to fill in details for himself. [Illustration: FIG. 158.—Plan and elevation of electric contact on vane post.] In-this case the vane is attached (Fig. 158) to a brass tube, closed at the upper end, and supported by a long spike stuck into the top of the pole. A little platform carries a brass ring, divided into as many insulated segments as the points which the vane is to be able to register. Thus, there will be eight segments if the half-points as well as the cardinal points are to be shown on the dial. The centre of each of these segments lies on a line running through the centre of the spike to the compass point to which the segment belongs. The tube moves with it a rotating contact piece, which rubs against the tops of the segments. Below it is a “brush” of strip brass pressing against the tube. This brush is connected with a wire running to one terminal of a battery near the dial. [Illustration: FIG. 159.—Magnetic recording dial.] The Dial.—This may be either vertical or horizontal, provided that the arrow is well balanced. The arrow, which should be of some light non-magnetic material, such as cardboard or wood, carries on its lower side, near the point, a piece of soft iron. Under the path of this piece is a ring of equally spaced magnets, their number equaling that of, the segments on the vane. Between arrow and magnets is the dial on which the points are marked (Fig. 159). Each segment is connected by a separate wire with the corresponding dial magnet, and each of these, through a common wire and switch, with the other terminal of the battery (Fig. 161). In order to ascertain the quarter of the wind, the switch is closed. The magnet which is energized will attract the needle to it, showing in what direction the vane is pointing. To prevent misreading, the dial may be covered by a flap the raising of which closes the battery circuit. A spring should be arranged to close the flap when the hand is removed, to prevent waste of current. [Illustration: FIG. 160.—Another type of electric dial with compass needle for pointer.] The exactitude of the indication given by the arrow depends on the number of vane segments used. If these are only four, a N. read- ing will be given by any position of the vane between N.E. and N.W.; if eight, N. will mean anything between N.N.E. and N.N.W. Telephone cables, containing any desired number of insulated wires, each covered by a braiding of a distinctive colour, can be obtained at a cost only slightly exceeding that of an equal total amount of single insulated wire. The cable form is to be preferred, on account of its greater convenience in fixing. The amount of battery power required depends on the length of the circuit and the delicacy of the dial. If an ordinary compass needle be used, as indicated in Fig. 160, very little current is needed. In this case the magnets, which can be made of a couple of dozen turns of fine insulated wire round a 1/8-in soft iron bar, should be arranged spokewise round the compass case, and care must be taken that all the cores are wound in the same direction, so as to have the same polarity. Otherwise some will attract the N. end of the needle and others repel it. The direction of the current flow through the circuit will decide the polarity of the magnets, so that, if one end of the needle be furnished with a little paper arrow-head, the “correspondence” between vane and dial is easily established. An advantage attaching to the use of a compass needle is that the magnet repels the wrong end of the needle. [Illustration: FIG. 161.—General arrangement of electric wind recorder.] The brush and segments must be protected from he weather by a cover, either attached to the segment platform or to the tube on which the vane is mounted. The spaces between the segments must be filled in flush with some non-conducting material, such as fibre, vulcanite, or sealing-wax; and be very slightly wider than the end of the contact arm, so that two segments may not be in circuit simultaneously. In certain positions of the vane no contact will be made, but, as the vane is motionless only when there is no wind or none to speak of, this is a small matter. About HackerNoon Book Series: We bring you the most important technical, scientific, and insightful public domain books. This book is part of the public domain. Archibald Williams (2005). Things To Make. Urbana, Illinois: Project Gutenberg. Retrieved https://www.gutenberg.org/cache/epub/14664/pg14664-images.html This eBook is for the use of anyone anywhere at no cost and with almost no restrictions whatsoever. You may copy it, give it away or re-use it under the terms of the Project Gutenberg License included with this eBook or online at , located at . www.gutenberg.org https://www.gutenberg.org/policy/license.html

WIND VANES WITH DIALS.

The Romance of Modern Mechanism by Archibald Williams is part of the HackerNoon Books Series. You can jump to any chapter in this book . CHAPTER XXI here A SELF-MOVING STAIRCASE At the American Exhibition, held in the Crystal Palace in 1902, there was shown a staircase which, on payment of a penny, transported any sufficiently daring person from the ground-floor to the gallery above. All that the experimenters had to do was to step boldly on, take hold of the balustrade, which moved at an equal pace with the stairs, and step off when the upper level was reached. The "escalator" (Latin = flight of stairs) hails from the United States, where it is proving a serious rival to the elevator. In principle, it is a continuously working lift, the slow travel of which is more than compensated by the fact that it is always available. The ordinary elevator is very useful in a large business or commercial house, where it saves the legs of people who, if they had to tramp up flight after flight of stairs, would probably not spend so much money as they would be ready to part with if their vertical travel from one floor to another was entirely free of effort. But the ordinary lift is, like a railway, intermittent. We all know what it means to stand at the grille and watch the cage slide downwards on its journey of, perhaps, four floors, when we want to go to a floor higher up. Rather than face the delay we use our legs. scalae Theoretically, therefore, a large emporium should contain at least two lifts. If the number be further increased, the would-be passenger will have a still better chance of getting off at once. Thus at the station of the Central London Railway we have to wait but a very few seconds before a grille is thrown back and an attendant invites us to "Hurry up there, please!" Yet there is delay while the cage is being filled. The actual journey occupies but a small fraction of the time which elapses between the moment when the first passenger enters the lift at the one end of the trip and the moment when the last person leaves it at the other end. In a building where the lift stops every fifteen feet or so to take people on or put them off, the waste of time is still more accentuated. The escalator is always ready. You step on and are transported one stage. A second staircase takes you on at once if you desire it. There is no delay. Furthermore, the room occupied by a single escalator is much less than that occupied by the number of lifts required to give anything like an equally efficient service. In large American stores, then, it is coming into favour, and also on the Manhattan Elevated Railway of New York. When once the little nervousness accompanying the first use has worn off, it eclipses the lift. A writer in Cassier's Magazine says: "In one large retail store during the holiday season more than 6,000 persons per hour have been carried upon the escalator for five hours of the day, and the aggregate for an entire day is believed to be 50,000. In the same store on an ordinary day the passengers alighting at the second floor from the eight large lifts, which run from the basement to the fifth floor, were counted, likewise the number at the escalator. This latter was found to be 859 per cent. of the number delivered by the eight lifts. In another establishment, in a very busy hour, the number taken from the first floor by the escalator was four times the number taken from the first floor by the fourteen lifts, which were running at their maximum capacity. To the merchant this spells opportunity for business. "The experience at the Twenty-third Street and Sixth Avenue station of the Manhattan Elevated Railway in New York, during a recent shut-down of the escalator, which has been in service for some time, is interesting as showing the attitude of the public, of which many millions have been carried by the installation during the several years of its operation. The daily traffic receipts of this station for a period beginning several weeks before the shut-down and extending as many after, for the years 1903 and 1902, and receipts of the adjacent stations for the same period were carefully plotted ... and the loss area during the period of shut-down was determined. The loss area was found to embrace 64,645 fares. It was, furthermore, daily a matter of observation that numbers of people, finding that the escalator was not running, refused to climb the stairs, and turned away from the station. "In the case of a great store, the escalator may be constructed as one continuous machine, with landings at each floor, and so arranged that steps which carry passengers up may perform a like service in carrying others down; or separate machines may be installed in various locations affording the best opportunity for displaying merchandise to the customer who may be proceeding from the lower to the upper floor. In the case of a six-storey building so equipped with escalator service in both directions, or in all ten escalator flights, it is obvious that the facilities are equal to an impossible number of elevators; and as facility of access has a direct bearing upon opportunities for business, it may well be argued that the relative value, measured by rent, of the main and upper floors is greatly changed." Each step in a staircase has two parts—the "tread" or horizontal board on which the foot is placed, and the vertical "riser" which acts both as a support to the tread above and also prevents the foot from slipping under the tread. In the escalator each tread is attached rigidly to its riser, and the two together form an independent unit. For the convenience of passengers in stepping on or off at the upper and lower landings, the treads in these places are all in the same horizontal plane. As they approach the incline the risers gradually appear, and the treads separate vertically. At the top of the incline the process is gradually reversed, the risers disappearing until the treads once more form a horizontal belt. The means of effecting this change is most ingenious. Each tread and its riser is carried on a couple of vertical triangular brackets, one at each side of the staircase. The base of the bracket is uppermost, to engage with the tread, and its apex has a hole through which passes a transverse bar, which in its central part forms a pin in the link-chain by which power is transmitted to the escalator. Naturally, the step would tip over. This is prevented by a yoke attached to each end of the bar, at right angles to it and parallel to the tread. The yoke has at each extremity a small wheel running on its own rail—there being two rails for each side of the staircase. Since step, brackets, bar, and yoke are all rigidly joined together, the step is unable to leave the horizontal, but its relation to the steps above and below is determined by the arrangement of the rails on which the yoke wheels run. When these are in the same plane, all the yokes, and consequently the treads, will also be in the same plane. But at the incline, where the inner rail gradually sinks lower than its fellow, the front wheel of one tread is lower than the front wheel of the next, and the risers appear. It may be added that, owing to the double track at each side of the staircase, the back wheel of one tread does not interfere with the front wheel of that below; and that on the level they come abreast without jostling, as the yoke is bent. The chain, of which the step-bars form pins, travels under the centre of the staircase. It is made up of links eighteen inches long, having, in addition to the bars, a number of steel cross-pins 112 inches in diameter, their axes three inches apart, so that the chain as a whole has a three-inch "pitch." The hubs of the links are bushed with bronze, and have a graphite "inlay," which makes them self-lubricating. Every joint is turned to within 11,000 inch of absolute accuracy. The tracks are of steel and hardwood, insulated from the ironwork which supports them by sheets of rubber. The wheels are so constructed as to be practically noiseless, so that as a whole the escalator works very quietly. "It has been observed," says the authority already quoted, "that beginners take pains to step upon a single tread, and that after a little experience no attention whatever is given to the footing, owing to the facility of adapting oneself to the situation. The upper landing is somewhat longer, thereby affording an interval for stepping off at either side of sufficient duration to meet the requirements of the aged and infirm. The sole function of the travelling landing is to provide a time interval to meet the requirements of the slowest-acting passenger, and not of the alert. The terminal of the exit landing, be it top or bottom (for the escalator operates equally well for either ascent or descent), is a barrier, called the shunt, of which the lower member travels horizontally in a plane oblique to the direction of movement of the steps, and at a speed proportionately greater, thereby imparting a right-angle resultant to the person or obstacle on the step which may come in contact with the shunt. By reason of this resultant motion, the person or obstacle is gently pushed off the end of the step upon the floor, without shock or injury in the slightest degree. The motion of the escalator is so smooth and constant that it does not interpose the least obstacle to the free movement of the passenger, who may walk in either direction or assume any attitude to the same degree as upon a stationary staircase." At Cleveland, U.S.A., there has been erected a rolling roadway, consisting of an inclined endless belt and platform made of planks eight feet long, placed transversely across the roadway. The timbers are fastened together in trucks of two planks each, adjoining trucks being joined by heavy links to form a moving roadway, which runs on 4,000 small wheels. At each end the roadway, which is continuous, passes round enormous rollers. Its total length is 420 feet, and the rise 65 feet. Four electric motors placed at regular intervals along its length, and all controlled by one man at the head of the incline, drive it at three miles an hour. It can accommodate six wagons at a time. About HackerNoon Book Series: We bring you the most important technical, scientific, and insightful public domain books. This book is part of the public domain. Archibald Williams (2014). The Romance of Modern Mechanism. Urbana, Illinois: Project Gutenberg. Retrieved https://www.gutenberg.org/cache/epub/46094/pg46094-images.html. This eBook is for the use of anyone anywhere at no cost and with almost no restrictions whatsoever. You may copy it, give it away or re-use it under the terms of the Project Gutenberg License included with this eBook or online at , located at . www.gutenberg.org https://www.gutenberg.org/policy/license.html

A SELF-MOVING STAIRCASE

Debian GNU/Linux: Guide to Installation and Usage by John Goerzen and Ossama Othman is part of the HackerNoon Books Series. You can jump to any chapter in this book . Advanced Topics here 13. Advanced Topics By now, you should have a strong base for which to build your GNU/Linux skills on. In this chapter we cover some very useful information regarding some advanced GNU/Linux features. 13.1 Regular Expressions A regular expression is a description of a set of characters. This description can be used to search through a file by looking for text that matches the regular expression. Regular expressions are analogous to shell wildcards (see section 6.6 on page [*]), but they are both more complicated and more powerful. A regular expression is made up of text and metacharacters. A metacharacter is just a character with a special meaning. Metacharacters include the following: . * [] - ^ $. If a regular expression contains only text (no metacharacters), it matches that text. For example, the regular expression “my regular expression” matches the text “my regular expression,” and nothing else. Regular expressions are usually case sensitive. You can use the egrep command to display all lines in a file that contain a regular expression. Its syntax is as follows: egrep ’regexp’ filename1 ... The single quotation marks are not always needed, but they never hurt. For example, to find all lines in the GPL that contain the word GNU, you type egrep ’GNU’ /usr/doc/copyright/GPL egrep will print the lines to standard output. If you want all lines that contain freedom followed by some indeterminate text, followed by GNU, you can do this: egrep ’freedom.*GNU’ /usr/doc/copyright/GPL The . means “any character,” and the * means “zero or more of the preceding thing,” in this case “zero or more of any character.” So .* matches pretty much any text at all. egrep only matches on a line-by-line basis, so freedom and GNU have to be on the same line. Here’s a summary of regular expression metacharacters: . Matches any single character except newline. * Matches zero or more occurrences of the preceding thing. So the expression a* matches zero or more lowercase a, and .* matches zero or more characters. [characters] The brackets must contain one or more characters; the whole bracketed expression matches exactly one character out of the set. So [abc]matches one a, one b, or one c; it does not match zero characters, and it does not match a character other than these three. ^ Anchors your search at the beginning of the line. The expression ^The matches The when it appears at the beginning of a line; there can’t be spaces or other text before The. If you want to allow spaces, you can permit 0 or more space characters like this: ^ *The. $ Anchors at the end of the line. end$ requires the text end to be at the end of the line, with no intervening spaces or text. [^characters] This reverses the sense of a bracketed character list. So [^abc] matches any single character, except a, b, or c. [character-character] You can include ranges in a bracketed character list. To match any lowercase letter, use [a-z]. You can have more than one range; so to match the first three or last three letters of the alphabet, try [a-cx-z]. To get any letter, any case, try [a-zA-Z]. You can mix ranges with single characters and with the ^metacharacter; for example, [^a-zBZ]means “anything except a lowercase letter, capital B, or capital Z.” () You can use parentheses to group parts of the regular expression, just as you do in a mathematical expression. || means “or.” You can use it to provide a series of alternative expressions. Usually you want to put the alternatives in parentheses, like this: c(ad|ab|at)matches cad or cab or cat. Without the parentheses, it would match cad or ab or at instead \ Escapes any special characters; if you want to find a literal *, you type *. The slash means to ignore *’s usual special meaning. Here are some more examples to help you get a feel for things: matches cope, cape, caper. c.pe c\ .pe matches , c.per. c.pe sto*p matches stp, stop, stoop. car.*n matches carton, cartoon, carmen. xyz.* matches xyz and anything after it; some tools, like egrep, only match until the end of the line. ^The matches The at the beginning of a line. atime$ matches atime at the end of a line. ^Only$ matches a line that consists solely of the word Only—no spaces, no other characters, nothing. Only Only is allowed. b[aou]rn matches barn, born, burn. Ver[D-F] matches VerD, VerE, VerF. Ver[^0-9] matches Ver followed by any non-digit. the[ir][re] matches their, therr, there, theie. [A-Za-z][A-Za-z]* matches any word which consists of only letters, and at least one letter. It will not match numbers or spaces. 13.2 Advanced Files Now that you have a basic understanding of files, it is time to learn more advanced things about them. 13.2.1 The Real Nature of Files: Hard Links and Inodes Each file on your system is represented by an inode (for Information Node; pronounced “eye-node”). An inode contains all the information about the file. However, the inode is not directly visible. Instead, each inode is linked into the filesystem by one or more hard links. Hard links contain the name of the file and the inode number. The inode contains the file itself, i.e., the location of the information being stored on disk, its access permissions, the file type, and so on. The system can find any inode if it has the inode number. A single file can have more than one hard link. What this means is that multiple filenames refer to the same file (that is, they are associated with the same inode number). However, you can’t make hard links across filesystems: All hard references to a particular file (inode) must be on the same filesystem. This is because each filesystem has its own set of inodes, and there can be duplicate inode numbers on different filesystems. Because all hard links to a given inode refer to the same file, you can make changes to the file, referring to it by one name, and then see those changes when referring to it by a different name. Try this: cd; echo "hello" > firstlink cd to your home directory and create a file called firstlink containing the word “hello.” What you’ve actually done is redirect the output of echo (echo just echoes back what you give to it), placing the output in firstlink. See the chapter on shells for a full explanation. cat firstlink Confirms the contents of firstlink. ln firstlink secondlink Creates a hard link: secondlink now points to the same inode as firstlink. cat secondlink Confirms that secondlink is the same as firstlink. ls -l Notice that the number of hard links listed for firstlink and secondlinkfiles!inodes is 2. echo "change" >> secondlink This is another shell redirection trick (don’t worry about the details). You’ve appended the word “change” to secondlink. Confirm this with cat secondlink. cat firstlink firstlink also has the word “change” appended! That’s because firstlink and secondlink refer to the same file. It doesn’t matter what you call it when you change it. chmod a+rwx firstlink Changes permissions on firstlink. Enter the command ls -l to confirm that permissions on secondlink were also changed. This means that permissions information is stored in the inode, not in links. rm firstlink Deletes this link. This is a subtlety of rm. It really removes links, not files. Now type ls -l and notice that secondlink is still there. Also notice that the number of hard links for secondlink has been reduced to one. rm secondlink Deletes the other link. When there are no more links to a file, Linux deletes the file itself, that is, its inode. All files work like this—even special types of files such as devices (e.g. /dev/hda). A directory is simply a list of filenames and inode numbers, that is, a list of hard links. When you create a hard link, you’re just adding a name-number pair to a directory. When you delete a file, you’re just removing a hard link from a directory. 13.2.2 Types of Files One detail we’ve been concealing up to now is that the Linux kernel considers nearly everything to be a file. That includes directories and devices: They’re just special kinds of files. As you may remember, the first character of an ls -l display represents the type of the file. For an ordinary file, this will be simply -. Other possibilities include the following: ddirectory
lsymbolic link
bblock device
ccharacter device
pnamed pipe
ssocket Symbolic Links Symbolic links (also called “symlinks” or “soft links”) are the other kind of link besides hard links. A symlink is a special file that “points to” a hard link on any mounted filesystem. When you try to read the contents of a symlink, it gives the contents of the file it’s pointing to rather than the contents of the symlink itself. Because directories, devices, and other symlinks are types of files, you can point a symlink at any of those things. So a hard link is a filename and an inode number. A file is really an inode: a location on disk, file type, permissions mode, etc. A symlink is an inode that contains the name of a hard link. A symlink pairs one filename with a second filename, whereas a hard link pairs a filename with an inode number. All hard links to the same file have equal status. That is, one is as good as another; if you perform any operation on one, it’s just the same as performing that operation on any of the others. This is because the hard links all refer to the same inode. Operations on symlinks, on the other hand, sometimes affect the symlink’s own inode (the one containing the name of a hard link) and sometimes affect the hard link being pointed to. There are a number of important differences between symlinks and hard links. Symlinks can cross filesystems. This is because they contain complete filenames, starting with the root directory, and all complete filenames are unique. Because hard links point to inode numbers, and inode numbers are unique only within a single filesystem, they would be ambiguous if the filesystem wasn’t known. You can make symlinks to directories, but you can’t make hard links to them. Each directory has hard links—its listing in its parent directory, its . entry, and the .. entry in each of its subdirectories—but to impose order on the filesystem, no other hard links to directories are allowed. Consequently, the number of files in a directory is equal to the number of hard links to that directory minus two (you subtract the directory’s name and the . link). comparing!hard links and symlinks You can only make a hard link to a file that exists, because there must be an inode number to refer to. However, you can make a symlink to any filename, whether or not there actually is such a filename. Removing a symlink removes only the link. It has no effect on the linked-to file. Removing the only hard link to a file removes the file. Try this: cd; ln -s /tmp/me MyTmp cd to your home directory. ln with the -s option makes a symbolic link - in this case, one called MyTmp that points to the filename /tmp/me. ls -l MyTmp Output should look like this: lrwxrwxrwx 1 havoc havoc 7 Dec 6 12:50 MyTmp -> /tmp/me The date and user/group names will be different for you, of course. Notice that the file type is l, indicating that this is a symbolic link. Also notice the permissions: Symbolic links always have these permissions. If you attempt to chmod a symlink, you’ll actually change the permissions on the file being pointed to. chmod 700 MyTmp You will get a No such file or directory error, because the file /tmp/me doesn’t exist. Notice that you could create a symlink to it anyway. mkdir /tmp/me Creates the directory /tmp/me. chmod 700 MyTmp Should work now. touch MyTmp/myfile Creates a file in MyTmp. ls /tmp/me The file is actually created in /tmp/me. rm MyTmp Removes the symbolic link. Notice that this removes the link, not what it points to. Thus you use rm not rmdir. rm /tmp/me/myfile; rmdir /tmp/me Lets you clean up after yourself. symlinks!removing Device Files Device files refer to physical or virtual devices on your system, such as your hard disk, video card, screen, and keyboard. An example of a virtual device is the console, represented by /dev/console. There are two kinds of devices:character and block. Character devices can be accessed one character at a time. Remember the smallest unit of data that can be written to or read from the device is a character (byte). Block devices must be accessed in larger units called blocks, which contain a number of characters. Your hard disk is a block device. You can read and write device files just as you can from other kinds of files, though the file may well contain some strange incomprehensible-to-humans gibberish. Writing random data to these files is probably a bad idea. Sometimes it’s useful, though. For example, you can dump a postscript file into the printer device /dev/lp0 or send modem commands to the device file for the appropriate serial port. /dev/null /dev/null is a special device file that discards anything you write to it. If you don’t want something, throw it in /dev/null. It’s essentially a bottomless pit. If you read /dev/null, you’ll get an end-of-file (EOF) character immediately. /dev/zero is similar, except that you read from it you get the \0 character (not the same as the number zero). Named Pipes (FIFOs) A named pipe is a file that acts like a pipe. You put something into the file, and it comes out the other end. Thus it’s called a FIFO, or First-In-First-Out, because the first thing you put in the pipe is the first thing to come out the other end. If you write to a named pipe, the process that is writing to the pipe doesn’t terminate until the information being written is read from the pipe. If you read from a named pipe, the reading process waits until there’s something to read before terminating. The size of the pipe is always zero: It doesn’t store data, it just links two processes like the shell |. However, because this pipe has a name, the two processes don’t have to be on the same command line or even be run by the same user. You can try it by doing the following: cd; mkfifo mypipe Makes the pipe. echo "hello" > mypipe & Puts a process in the background that tries to write “hello” to the pipe. Notice that the process doesn’t return from the background; it is waiting for someone to read from the pipe. cat mypipe At this point, the echo process should return, because cat read from the pipe, and the cat process will print hello. rm mypipe You can delete pipes just like any other file. Sockets Sockets are similar to pipes, only they work over the network. This is how your computer does networking. You may have heard of “WinSock,” which is sockets for Windows. We won’t go into these further because you probably won’t have occasion to use them unless you’re programming. However, if you see a file marked with type son your computer, you know what it is. 13.2.3 The proc Filesystem The Linux kernel makes a special filesystem available, which is mounted under /proc on Debian systems. This is a “pseudo-filesystem” because it doesn’t really exist on any of your physical devices. The proc filesystem contains information about the system and running processes. Some of the “files” in /proc are reasonably understandable to humans (try typing cat /proc/meminfo or cat /proc/cpuinfo); others are arcane collections of numbers. Often, system utilities use these to gather information and present it to you in a more understandable way. People frequently panic when they notice one file in particular— /proc/kcore —which is generally huge. This is (more or less) a copy of the contents of your computer’s memory. It’s used to debug the kernel. It doesn’t actually exist anywhere, so don’t worry about its size. If you want to know about all the things in /proc, type man 5 proc. 13.2.4 Large-Scale Copying Sometimes you may want to copy one directory to another location. Maybe you’re adding a new hard disk and you want to copy /usr/local to it. There are several ways you can do this. The first is to use cp. The command cp -a will tell cp to do a copy preserving all the information it can. So, you might use cp -a /usr/local /destination However, there are some things that cp -a won’t catch[1]. So, the best way to do a large copy job is to chain two tar commands together, like so: [1] Sparse files and hard links are two examples. tar -cSpf - /usr/local | tar -xvSpf -
-C /destination The first tar command will archive the existing directory and pipe it to the second. The second command will unpack the archive into the location you specify with -C. 13.3 Security Back in section 7.1 on page [*], we discussed file permissions in Linux. This is a fundamental way to keep your system secure. If you are running a multi-user system or a server, it is important to make sure that permissions are correct. A good rule of thumb is to set files to have the minimum permissions necessary for use. If you are running a network server, there are some other things to be aware of as well. First, you ought to uninstall or turn off any network services you’re not using. A good place to start is the file /etc/inetd.conf; you can probably disable some of these. For most network services, it’s also possible to control who has access to them; the /etc/hosts.allow and /etc/hosts.deny files (documented in man 5 hosts_access) can control who has access to which services. You also ought to keep up-to-date with patches or updates to Debian; these can be found on your nearest Debian FTP mirror. Some other commonsense rules apply: ◼ Never tell anyone your password. ◼ Never send your password in cleartext across the Internet by using something like telnet or FTP. Instead, use encrypted protocols or avoid logging in remotely. ◼ Avoid using root as much as possible. ◼ Don’t install untrusted software, and don’t install it as root. ◼ Avoid making things world-writable whenever possible. /tmp is one exception to this rule. While this is probably not of as much use to somebody not running a server, it is still pays to know a bit about security. Debian’s security mechanism is what protects your system from many viruses. 13.4 Software Development with Debian Debian makes a great platform for software development and programming. Among the languages and near-languages it supports are: C, C++, Objective-C, Perl, Python, m4, Ada, Pascal, Java, awk, Tcl/Tk, SQL, assembler, Bourne shell, csh, and more. Writing programs is beyond the scope of this book, but here are some of the more popular development programs in Debian: gcc The GNU C Compiler, a modern optimizing C compiler. g++ The C++ compiler from the gcc line. cpp The C preprocessor from gcc. perl The Perl interpreter. Perl is a great “glue” language. gdb GNU Debugger, used to debug programs in many different languages. gprof Used for profiling, this program helps you to find ways to improve the performance of your programs. emacs GNU Emacs is a programmers’ editor and IDE. as The GNU Assembler. About HackerNoon Book Series: We bring you the most important technical, scientific, and insightful public domain books. This book is part of the public domain. John Goerzen and Ossama Othman (2004). Debian GNU/Linux : Guide to Installation and Usage. Urbana, Illinois: Project Gutenberg. Retrieved https://www.gutenberg.org/cache/epub/6527/pg6527-images.html This eBook is for the use of anyone anywhere at no cost and with almost no restrictions whatsoever. You may copy it, give it away or re-use it under the terms of the Project Gutenberg License included with this eBook or online at , located at . www.gutenberg.org https://www.gutenberg.org/policy/license.html

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