Command Line

Use Case

A Use Case is a thing an actor perceives from the system. A Use Case maps actors with functions. Importantly, the actors need not be people. As an example, a system can perform the role of an actor, when it communicate with another system. In another angle a Use Case encodes a typical user interaction with the system. In particular, it: Captures some user-visible function. Achieves some concrete goal for the user. A complete set of Use Cases largely defines the requirements for your system: everything the user can see, and would like to do.

less

A sophisticated interactive pager program for looking at information on a terminal, one screenful (or "page") at a time. The name is a pun on the more program.

bc

Arbitrary precision calculator

crontab

Automate commands

csplit

Break files at specific locations.

cc

C compiler

ctags

C function references (for vi)

splint

C program analyzer

lprm

Cancel a printer request

chmod

Change access modes on files.

cd

Change directory

chgrp

Change file group

chown

Change file owner.

Class Diagram

Class diagrams are widely used to describe the types of objects in a system and their relationships. Class diagrams model class structure and contents using design elements such as classes, packages and objects. Class diagrams describe three different perspectives when designing a system, conceptual, specification, and implementation. These perspectives become evident as the diagram is created and help solidify the design. The Class diagrams, physical data models, along with the system overview diagram are in my opinion the most important diagrams that suite the current day rapid application development requirements.

clear

Clear the screen

dircmp

Compare directories

comm

Compare items in two sorted files

diff3

Compare three different files

cmp

Compare two files, byte by byte

diff

Compare two files, line by line.

sdiff

Compare two files, side by side.

gzip

Compress files to free up space

ssh

Connect to another system securely

cpio

Copy archives in or out

cp

Copy files

scp

Copy files to remote system securely.

ln

Create filename aliases.

file

Determine a file's type

cal

Display calendar

zcat

Display contents of compressed files

gzcat

Display contents of compressed files (may be linked to zcat)

more

Display files by screenful

finger

Display information about users

date

Display or set date

strings

Display text strings found in binary files

od

Dump input in various formats

make

Execute commands in a specified order

at

Execute commands later

gunzip

Expand compressed (.gz and .z) files

bunzip2

Expand files compressed with bzip2 (.bz2 files)

tar

File tree and tape archiver

locate

Find a file somewhere on the system based on its name. The program uses a database of files that is usually automatically rebuilt, nightly.

uniq

Find repeated or unique lines in a file

printf

Format and print command-line arguments

iconv

General-purpose character-encoding conversion tool

man

Get information on a command

lpq

Get printer status

ftp

Interactive File Transfer Program

lex

Lexical analyzer generator

top

List every program running

ls

List files or Directories

ld

Loader

mkdir

Make a directory

banner

Make posters from words

paste

Merge columns or switch order

join

Merge different columns into a database

Method Overloading

Method overloading is the ability to define several methods all with the same name. public class MyLogger { public void LogError(Exception e) { // Implementation goes here } public bool LogError(Exception e, string message) { // Implementation goes here } }

Method Overriding

Method overriding is a language feature that allows a subclass to override a specific implementation of a method that is already provided by one of its super-classes. A subclass can give its own definition of methods but need to have the same signature as the method in its super-class. This means that when overriding a method the subclass's method has to have the same name and parameter list as the super-class' overridden method. using System; public class Complex { private int real; public int Real { get { return real; } } private int imaginary; public int Imaginary { get { return imaginary; } } public Complex(int real, int imaginary) { this.real = real; this.imaginary = imaginary; } public static Complex operator +(Complex c1, Complex c2) { return new Complex(c1.Real + c2.Real, c1.Imaginary + c2.Imaginary); } public override string ToString() { return (String.Format("{0} + {1}i", real, imaginary)); } } In above example I have extended the implementation of the sample Complex class given under operator overloading section. This class has one overridden method named ToString, which overrides the default implementation of the standard ToString method to support the correct string conversion of a complex number.

MVC

Model The classes which are used to store and manipulate state, typically in a database of some kind. View The user interface bits (in this case, HTML) necessary to render the model to the user. Controller The brains of the application. The controller decides what the user's input was, how the model needs to change as a result of that input, and which resulting view should be used.

sed

Non-interactive text editor

yacc

Parser generator. Can be used with lex

sleep

Pause during processing

expr

Preform arithmetic and comparisons

nohup

Preserve a running job after logging out

md5sum

Print a file checksum using the Message Digest 5 (MD5) algorithm.

cksum

Print a file checksum, POSIX standard algorithm.

dirname

Print all but the last component of a pathname.

basename

Print the last component of a pathname, optionally removing a suffix.

id

Print user and group ID and name information

pwd

Print working directory

xargs

Process many arguments in manageable portions

script

Produce a transcript of your login session

fmt

Produce roughly uniform line lengths

line

Read a line of input

mailx

Read or send mail

nice

Reduce a job's priority

strip

Remove data from an object file

rmdir

Remove directories

rm

Remove files

echo

Repeat command-line arguments on the output

spell

Report misspelled words

fgrep

Search files for literal words

find

Search the system for filenames matching patterns or attributes

cut

Select columns for display

lpr

Send to the printer

stty

Set or display terminal settings

passwd

Set your login password

du

Show disk usage

env

Show environment variables

df

Show free disk space

ps

Show processes

head

Show the first few lines of a file.

tail

Show the last few lines of a file

who

Show who is logged on

slogin

Sign on to remote Unix using secure shell.

sort

Sort or merge files

split

Split files evenly

biff

Stands for "A dog named Biff" This command, which turns on asynchronous mail notification, was actually named after a dog. Courtesy of Eric Cooper, Carnegie Mellon University: "I can confirm the origin of biff, if you're interested. Biff was Heidi Stettner's dog, back when Heidi (and I, and Bill Joy) were all grad students at U.C. Berkeley and the early versions of BSD were being developed. Biff was popular among the residents of Evans Hall, and was known for barking at the mailman, hence the name of the command."

cat

Stands for "Catenate" "Catenate" is an obscure word meaning "to connect in a series", which is what the cat command does to one or more files. This is not to be confused with C/A/T, the Computer Aided Typesetter.

egrep

Stands for "Extended grep" The egrep command uses fancier regular expressions than the grep command. Many people use the egrep command for its internal algorithms, which are more sophisticated than the grep and fgrep commands. Also, the egrep command is usually the fastest of the three programs.

grep

Stands for "Global regular expression print" The grep command is used to print all lines matching a certain pattern grep [OPTIONS] PATTERN [FILE...] grep searches the named input FILEs (or standard input if no files are named, or if a single hyphen-minus (-) is given as file name) for lines containing a match to the given PATTERN. By default, grep prints the matching lines.

nroff, troff

Stands for "New roff, Typesetter new roff" These two commands are descendants of the roff command, which was a re-implementation of the Multics runoff program. The runoff program would "run off" a good copy of a document.

Perl

Stands for "Practical extraction and report language" The Perl language is a text, process, and file manipulation tool, created by Larry Wall. Perl bridges the gap between shell and C programming, and is free and completely portable. The acronym is one of many variants proposed, with varying degrees of seriousness, as the true origin of the name. However, this is currently regarded as apocryphal.

RDDs

Stands for "Resilient Distributed Datasets" RDD is a logical reference of a dataset which is partitioned across many server machines in the cluster. RDDs are Immutable and are self recovered in case of failure. dataset could be the data loaded externally by the user.

SOA

Stands for "System Oriented Architecture" A collection of encapsulated services which communicate over a network, are joined through loose coupling, and can be joined, deleted, and reused in other places in the architecture. This allows companies and designs to be more agile.

tee

Stands for "T" The tee command is named after plumbing terminology for a T-shaped pipe splitter. This Unix command splits the output of another command, sending it to a file and to the terminal.

rc

Stands for "runcom (as in .cshrc or /etc/rc)" The rc command derives from the runcom facility from the MIT CTSS system, ca. 1965. From Brian Kernighan and Dennis Ritchie, as told to Vicki Brown: "There was a facility that would execute a bunch of commands stored in a file; it was called runcom for "run commands", and the file began to be called "a runcom". rc in Unix is a fossil from that usage."

su

Switch to a different user

test

Test a condition

tcsh

The "Tenex" C shell: A much enhanced version of csh

info

The GNU info system for online documentation

pdksh

The Public Domain Korn shell

awk

The awk scripting language was named by its authors, Al Aho, Peter Weinberger, and Brian Kernighan. awk 'pattern {action}' input-file > output-file This means: take each line of the input file; if the line contains the pattern apply the action to the line and write the resulting line to the output-file.

Data Access Layer

The data access layer (DAL), which is a key part of every n-tier system, is mainly consist of a simple set of code that does basic interactions with the database or any other storage device. These functionalities are often referred to as CRUD (Create, Retrieve, Update, and Delete). The data access layer need to be generic, simple, quick and efficient as much as possible. It should not include complex application/ business logics.

Operator Overloading

The operator overloading (less commonly known as ad-hoc polymorphisms) is a specific case of polymorphisms in which some or all of operators like +, - or == are treated as polymorphic functions and as such have different behaviors depending on the types of its arguments. public class Complex { private int real; public int Real { get { return real; } } private int imaginary; public int Imaginary { get { return imaginary; } } public Complex(int real, int imaginary) { this.real = real; this.imaginary = imaginary; } public static Complex operator +(Complex c1, Complex c2) { return new Complex(c1.Real + c2.Real, c1.Imaginary + c2.Imaginary); } } I above example I have overloaded the plus operator for adding two complex numbers. There the two properties named Real and Imaginary has been declared exposing only the required "get" method, while the object's constructor is demanding for mandatory real and imaginary values with the user defined constructor of the class.

csh

The original BSD C shell

sh

The original Bourne shell, particularly on commercial Unix systems.

Three-Tier Architecture

The three-tier architecture has the following three tiers: Presentation Tier or Web Server: User Interface, displaying/ accepting data/ input to/ from the user Application Logic/ Business Logic/ Transaction Tier or Application Server: Data validation, acceptability check before being added to the database and all other business/ application specific operations Data Tier or Database server: Simple reading and writing method to database or any other storage, connection, command, stored procedures etc

strace

Trace signals and system calls

truss

Trace signals and system calls

tr

Translate (redefine) characters

bzip2

Very high quality file compression program

vi

Visual text editor

Polymorphism

a programming language's ability to process objects differently depending on their data type or class. More specifically, it is the ability to redefine methods for derived classes.

wc

count lines, words, and characters

Find (unix)

find <startingpoint> <options> <search term>

pr

format and paginate for printing.

ex

line editor underlying vi

mv

move or rename files or directories

kill

terminate a running command

bash

the GNU Project's Bourne Again Shell

ksh

the Korn shell, either an original or clone, depending on the operating system

zsh

the Z-shell