Intro to Shell Programming: Writing a Simple Web Gallery

A Simple Script

So you're not a programmer, you say? If you can string a few shell commands together, it's not much of a step from there to programming.

To demonstrate that, I'll take you through the steps of writing a very simple web gallery script: one that will take your images and build a little web page to show them off.

Your script will need to do some image operations like resizing from the command-line. For that, I recommend ImageMagick, available as a package in just about every Linux distro. Just apt-get install imagemagick or yum install imagemagick or whatever your distro prefers, and you're ready to go. If you prefer GraphicsMagick, a fork of ImageMagick, that's okay too. All the basic commands are the same.

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For this project, you'll also want a directory with some images in it. You can create a directory with mkdir dirname or use your favorite file manager. Then copy some images into it. Be sure to copy, not move: you'll be making changes to images in this directory, and you wouldn't want to overwrite the originals.

In a shell, change directory (cd) into your new image directory; you'll be running your script from there.

Create your shell script

To create your shell script, use a text editor, not a word processor like OpenOffice. If you don't have a favorite text editor yet, check out the recent LinuxPlanet articles on Kate.

A shell script is, at its most basic, a list of commands you want the shell to run. It starts with a magic line:

#! /bin/sh

That's called a shebang line, because the # character is usually pronounced "hash" and the !, "bang". It lets you run your script like a program, by just typing the program name, and Linux will figure out that it's a shell script, run by the shell, /bin/sh.

There's one other step you need before you can run your shell script: you need to make it executable. Choose a file name (say, gal for gallery) and save your shell script. Then, in a shell, you can change its permissions this way:

chmod ugo+x gal

(that means "Make the file executable for user, group and other.") If you prefer using gui tools, right-click on your newly created script, choose Properties and look for the Permissions tab: you can make the script executable there.

Now you have a shell script, and it's runnable. But it doesn't do anything. That's the next step.