Writing HTML with m4
It's amazing how easy it is to write simple HTML pages—and the availability of WYSIWYG (what you see is what you get) HTML editors like Netscape Gold lulls one into a mood of “don't worry, be happy”. However, managing multiple, inter-related pages of HTML rapidly gets very difficult. I recently had a slightly complex set of pages to put together, and I started thinking, “there has to be an easier way.”
I immediately turned to the WWW and looked up all sorts of tools—but quite honestly I was rather disappointed. Mostly, they were what I would call “typing aids”—instead of having to remember arcane incantations like <a href="link"7gt;text</a> text, you are given a button or a magic keychord like alt-ctrl-j which remembers the syntax and does all the typing for you.
Linux to the rescue—since HTML is built as ordinary text files, the normal Linux text management tools can be used. This includes revision control tools such as rcs and the text manipulation tools like awk, Perl, etc. These tools offer significant help in version control and managing development by multiple users as well as automating the process of displaying information from a database (the classic grep |sort |awk pipeline).
The use of these tools with HTML is documented elsewhere, e.g., Jim Weirich's article in Linux Journal Issue 36, April 1997, “Using Perl to Check Web Links”. I highly recommend this article as yet another way to really flex those Linux muscles when writing HTML.
What I will cover here is work I've done recently using the pre-processor m4 to maintain HTML. The ideas can very easily be extended to the more general SGML case.
I decided to use m4 after looking at various other pre-processors including cpp, the C front-end, which is perhaps a little too C-specific to be useful with HTML. m4 is a generic and clean macro expansion program, and it's available under most Unices including Linux.
Instead of editing *.html files, I create *.m4 files with my favourite text editor. These files look something like the following:
m4_include(stdlib.m4) _HEADER(`This is my header') <P>This is some plain text<P> _HEAD1(`This is a main heading') <P>This is some more plain text<P> _TRAILER
The format is just HTML code, but you can include files and add macros rather like in C. I use a convention that my new macros are in capitals and start with an _ character to make them stand out from HTML language and to avoid name-space collisions.
The m4 file is then processed as follows to create an .html file using the command:
m4 -P <file.m4 >file.html
This process is especially easy if you create a makefile to automate these steps in the usual way. For example:
.SUFFIXES: .m4 .html .m4.html: m4 -P <$*.m4 >$*.html DEFault: index.html *.html: stdlib.m4 all: default PROJECT1 PROJECT2 PROJECT1: (cd project2; make all) PROJECT2: (cd project2; make all)Some of the most useful commands in m4 are listed here with their cpp equivalents shown in parentheses:
m4_include: includes a common file into your HTML (#include)
m4_define: defines an m4 variable (#define)
m4_ifdef: a conditional (#ifdef)
m4_changecom: change the m4 comment character (normally #)
m4_debugmode: control error diagnostics
m4_traceon/off: turn tracing on and off
m4_incr, m4_decr: simple arithmetic
m4_eval: more general arithmetic
m4_esyscmd: execute a Linux command and use the output
m4_divert(i): This is a little complicated, so skip on first reading. It is a way of storing text for output at the end of normal processing. It will come in useful later, when we get to automatic numbering of headings. It sends output from m4 to a temporary file number i. At the end of processing, any text which was diverted is then output, in the order of the file number i. File number -1 is the bit bucket and can be used to comment out chunks of comments. File number 0 is the normal output stream. Thus, for example, you can use m4_divert to divert text to file 1, and it will only be output at the end.
|Making Linux and Android Get Along (It's Not as Hard as It Sounds)||May 16, 2013|
|Drupal Is a Framework: Why Everyone Needs to Understand This||May 15, 2013|
|Home, My Backup Data Center||May 13, 2013|
|Non-Linux FOSS: Seashore||May 10, 2013|
|Trying to Tame the Tablet||May 08, 2013|
|Dart: a New Web Programming Experience||May 07, 2013|
- RSS Feeds
- Making Linux and Android Get Along (It's Not as Hard as It Sounds)
- New Products
- Drupal Is a Framework: Why Everyone Needs to Understand This
- A Topic for Discussion - Open Source Feature-Richness?
- Home, My Backup Data Center
- Validate an E-Mail Address with PHP, the Right Way
- New Products
- Tech Tip: Really Simple HTTP Server with Python
- Developer Poll
- git-annex assistant
46 min 10 sec ago
- direct cable connection
1 hour 8 min ago
- Agreed on AirDroid. With my
1 hour 18 min ago
- I just learned this
1 hour 23 min ago
1 hour 53 min ago
- not living upto the mobile revolution
4 hours 44 min ago
- Deceptive Advertising and
5 hours 20 min ago
- Let\'s declare that you have
5 hours 20 min ago
- Alterations in Contest Due
5 hours 22 min ago
- At a numbers mindset, your
5 hours 23 min ago
Enter to Win an Adafruit Prototyping Pi Plate Kit for Raspberry Pi
It's Raspberry Pi month at Linux Journal. Each week in May, Adafruit will be giving away a Pi-related prize to a lucky, randomly drawn LJ reader. Winners will be announced weekly.
Fill out the fields below to enter to win this week's prize-- a Prototyping Pi Plate Kit for Raspberry Pi.
Congratulations to our winners so far:
- 5-8-13, Pi Starter Pack: Jack Davis
- 5-15-13, Pi Model B 512MB RAM: Patrick Dunn
- Next winner announced on 5-21-13!
Free Webinar: Linux Backup and Recovery
Most companies incorporate backup procedures for critical data, which can be restored quickly if a loss occurs. However, fewer companies are prepared for catastrophic system failures, in which they lose all data, the entire operating system, applications, settings, patches and more, reducing their system(s) to “bare metal.” After all, before data can be restored to a system, there must be a system to restore it to.
In this one hour webinar, learn how to enhance your existing backup strategies for better disaster recovery preparedness using Storix System Backup Administrator (SBAdmin), a highly flexible bare-metal recovery solution for UNIX and Linux systems.