Command Line Media / "Media Bashing"
While the command line, or shell, is a text-based interface, this does not mean that manipulating other kinds of media, image, sound, video, is excluded. Far from it, many command line tools offer extremely useful and uniquely powerful functionality difficult to achieve with GUI programs. In addition, by applying the basics of pipelining and abstraction (through creating your own scripts with parameters), the command line enables highly particular and personal media tools to be created by pulling existing tools together in novel ways.
Considering the difference between graphical / interactive software and textual / non-interactive, you could compare:
|graphical / interactive||command-line / non-interactive|
|the GIMP or Photoshop||ImageMagick|
|Cinelerra or Final Cut||ffmpeg|
So the difference is not simply whether a program uses graphics or not -- Command-line programs are designed to perform a very specific task, and typically are specified textually according to a strict syntax (command-line options, etc.) They are non-interactive in the sense that you start them up, they do their thing, and you get the result -- you don't typically influence them while they are running. However, you often can work interactively with these programs through cycles of making changes to a script, running it, observing the result and repeating.
Making a "frontpage" snapshot tool
An exercise to build a simple tool to support visual comparison of front pages newssites a la Sarah Charlesworth's Modern History (1978). The work, among many other works of interest, can be seen as part of the Order Of Things exhibition until Jan 4, 2009 at the MuKHA, Antwerp.
Exercise explores the principle of:
- simple command line tools focused on doing a simple task
- the idea of a pipeline to join various commands together
- introducing the concept of a variable to make a personal "tool"
- cron jobs to automate a process over a long time period
Getting a grip on a tool
Command line programs, as focused and "simple" as they may be, often take some time to get used to. The initial man-page dump of possible options may seem overwhelming at first, but if you simply have a little discipline to try some variations, and above all to record your successes (in a text file and/or by taking notes on a printed copy of a man page), you can soon feel comfortable to use the new program.
We start with the tool wget.
First, simply try to run it:
Too much information! A pipeline to the rescue!
wget --help | less
Man has an option to output print-friendly postscript output. It's described on the "man" man page. (That's right: "man man"!)
man -t wget
man -t wget > wget.ps
Now you can print the postscript file, or view with a viewer like evince:
Necessary Tools / Topics
- Shell basics: cd, pwd, mv, cp
- Connecting to a "remote" server with ssh
- ImageMagick: montage
- man pages
- command line options
Examples of wget
Start from these examples, culled from the web. Try the examples out, alter the options. Find the options used in the (printed) man page of wget. Collect working (or interesting non-working) commands in a text file, and add comments to remind yourself why they were noteworthy.
To download all the files in a "directory listing":
wget -r -np -nd http://example.com/packages/
wget -r -nd -np --follow-tags=img http://www.colourlovers.com -A.jpg,.jpeg montage *.jpg ../public_html/montage.jpg
Blurps out this file:
(Notice the wget is run from a different directory the where the picture is placed)
Assignment for next week
Chapter 4 introduces some Turtle Graphics!