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Medium 9780596006280

The Shell

Barrett, Daniel J. O'Reilly Media ePub

In order to run commands on a Linux system, you'll need somewhere to type them. That "somewhere" is called the shell, which is Linux's command-line user interface: you type a command and press Enter, and the shell runs whatever program (or programs) you've requested. To run a shell, see Fedora: A First View.

For example, to see who's logged in, you could execute this command in a shell:

(The dollar sign is the shell prompt, which means the shell is ready to run a command.) A single command can also invoke several programs at the same time, and even connect programs together so they interact. Here's a command that redirects the output of the who program to become the input of the wc program, which counts lines of text in a file; the result is the number of lines in the output of who:

telling you how many users are logged in.[7] The vertical bar, called a pipe, makes the connection between who and wc.

A shell is actually a program itself, and Linux has several. We focus on Bash (the "Bourne-Again Shell"), located in /bin/bash, which is the Fedora Linux default.

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Medium 9780596101619

Map Local Weather Conditions

Rich Gibson O'Reilly Media PDF



Map Local Weather Conditions

uses a spatial query against PostGIS, a set of spatial extensions to PostgreSQL, to determine which district contains the given point. Finally, it passes the answer back to the site’s JavaScript in your browser.

You can find out more about PostGIS at http://postgis. O’Reilly’s Web Mapping Illustrated offers a good tutorial on PostGIS, as well.

Similarly, lets you navigate crimes by city ward, and there’s a “Find your ward” feature on the ward page: http://www. For ward and ZIP Code pages, uses the Google Maps polyline-drawing API to draw the border for the given ward or ZIP Code on the map. I did this by obtaining the ward and ZIP

Code boundaries in ESRI Shapefile format from the City of Chicago’s GIS department at I loaded the shapefiles into a

PostgreSQL database and converted the data into longitude-latitude coordinates using the conversion functions in PostGIS. Finally, it was just a matter of feeding the points into the Google Maps polyline-drawing API, and voila: we have ward and ZIP Code borders.

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Medium 9780596101398

9. Alternative UIs

Jack D. Herrington O'Reilly Media ePub

Use MapServer and PHP to build dynamic maps within your web application.

There has been a recent surge in the popularity of digital mapping. Part of this has been fueled by access to open source mapping tools and free geospatial data; it also hasn't hurt to see killer applications like Google Maps and MapQuest come on the scene. These are popular incarnations of some exciting web mapping technology that you too can use. With a few pieces of mapping data, a mapping programming library, and a PHP script, almost anyone can create custom and interactive maps.

Several open source mapping tools are available, from desktop applications to web-enabled mapping services. One of these is the University of Minnesota MapServer ( With a large user base, active community, and dedicated developers, it is a powerful product for publishing maps over the Web.

MapServer is actively used as the back end to many PHP web page frontends. For example, the Chameleon ( and Mapbender ( products both use PHP extensively. Also available is a powerful implementation of Ajax-based web mapping called ka-Map.

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Medium 9780596009502

15. Gathering Data with Forms

Jessica Mantaro O'Reilly Media ePub

As you know by now, FrontPage can really help you get your message out to the world. And if you're like most Web authors, you've probably filled your pages with content and formatted them nicely for the viewing pleasure of your visitors. But what if you want to let your audience reciprocate and tell you a thing or two? Maybe you've wondered how to create user registration forms so you know who's visiting your site, or perhaps you'd like to create a discussion section where viewers can see messages posted by others and submit a response.

When you want to gather information from viewers, you'll need to create a Web form: an HTML page that includes interactive fields in which a visitor can type or make a selection. You've probably filled out thousands of forms yourselfto do things like subscribe to the PTA newsletter or access your Web-based email account.

This chapter introduces you to forms and the many ways FrontPage lets you manage them. You can create your own form manually or use a FrontPage form template (a ready-made form-creating tool). You'll learn how to collect the data you're receiving in a variety of formatsfrom email to text files, or you can even pipe the info you're gathering into a database. And you'll also learn a few form-related tricks, like how to make sure that visitors fill in certain fields and how to let them know they've successfully filled out and submitted your form.

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Medium 9781937538576

5 Exposure and Metering

Glenn Rand Rocky Nook-IPS ePub

© Tim Meyer

Exposure refers to the capture of light on the camera’s sensor or film. Factors affecting exposure include the camera’s aperture and shutter speed as well as the speed of the sensor or film. When any one of these three factors remains constant, then the other two variables establish the exposure.

Though many portrait photographers believe they do not need to consider shutter speed because they use electronic flash, there are several situations where the shutter speed is crucial, such as when needing to include an unlighted background.

All photography is based on a 2:1 factor. Doubling the ISO increases the film or sensor’s sensitivity by a factor of 2. Both f-stops and shutter speeds are based on this doubling/halving function.

If the ISO is held constant (the method used for film), then f/4 at 1/125, f/5.6 at 1/60, f/8 at 1/30, and f/11 at 1/15 will all be equivalent exposures. (With digital sensors, the ISO is flexible.)

If the shutter speed is held constant, then f/11 at 400 ISO, f/8 at 200 ISO, and f/5.6 at 100 ISO will all be equivalent exposures.

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