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LinuxWorld: Using the m4 Macro Processor

Apr 26, 2000, 15:43 (0 Talkback[s])
(Other stories by Paul Dunne)

[ Thanks to S.Ramaswamy for this link. ]

"Chief among the the unsung heroes of Linux and Unix is m4. Unsung? Well, for instance, although m4 has been a standard part of Unix since version 7, no mention is made of it in that great O'Reilly & Associates book, Unix Power Tools. What is it about m4 that makes it so useful, and yet so overlooked? m4 -- a macro processor -- unfortunately has a dry name that disguises a great utility. A macro processor is basically a program that scans text and looks for defined symbols, which it replaces with other text or other symbols. Thus, m4 is a powerful general-purpose utility that can be used to automate many tasks people often end up doing in sed, awk, perl, and even their favorite text editor. Even so, it still doesn't seem like a macro processor is that big of a deal. Unix developers already have a built-in macro processor, in the form of the C preprocessor, in their compiler. Perhaps this is what accounts for m4's relative neglect. Whatever the case may be, this article will show Linux users the power and usefulness of this software tool."

"The contemporary implementation of m4 on a Linux system is GNU m4, which follows System V Release 3 m4, with extensions. I am aware of no other version of m4 that has been ported to Linux. m4 implementations on BSD may differ slightly. However, m4 is m4, and this article should be useful for other Unix users, too. The latest version is 1.4, which was released in October 1994."

"The most important of the built-in macros is define(), which allows users to define their own macros. For example, define(author, Paul Dunne) defines a macro "author" -- any occurrence of which will expand to the string "Paul Dunne". m4 expands macro names into their defining text as soon as it possibly can."

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