String substitution language, a more general macro facility than the C preprocessor, first really publicised as the '''macro''' processor for [Ratfor] in the book [Software Tools]. It's a sophisticated language, but tricky to use because there's no unique substitution symbol to distinguish macros from ordinary running text.

The [GNU] m4 home page is [http://www.gnu.org/software/m4/m4.html].

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[DKF]: M4 is Turing-Complete, but only really used for [autoconf] hacking now (and that's a fairly heavily modified version).

[Peter da Silva]: It's also used in sendmail for automating the generation of config files.

Back around '82, after I left Berkeley, I was using RSX-11 and feeling UNIX-starved. I took a copy of [Software Tools] and implemented everything in it from '''Ratfor''' through '''ed'''. When I implemented '''macro''' I renamed all the internal symbols so they began with a dollar sign. This made a huge difference in the usability of the language.

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[http://www.linuxselfhelp.com/gnu/autoconf/html_chapter/autoconf_8.html#SEC85] explains the basic syntax of m4, although it is mostly about m4 [quoting hell].

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[LV] So, are there enough benefits to m4 to make it worth a developer's time to use it
with Tcl to write sort of metacode, which would be expanded before execution?
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''[escargo] 28 May 2005'' - I one received several technical reports (I believe from Bell Labs,
but I could be wrong) about different software they had made available, and one of them was for
the '''m6''' macro processor.  I don't know how m4 and m6 differred (nor what happened to m5),
but I used to be an avid follower of macro language development (primarily for the purposes of
software portability).  Anybody else remember anything about m6?
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[Category Language]