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9 Programming in M4sh
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M4sh, pronounced "mash", is aiming at producing portable Bourne shell
scripts.  This name was coined by Lars J. Aas, who notes that, according
to the Webster's Revised Unabridged Dictionary (1913):

     Mash \Mash\, n.  [Akin to G. meisch, maisch, meische, maische,
     mash, wash, and prob. to AS. miscian to mix.  See "Mix".]

       1. A mass of mixed ingredients reduced to a soft pulpy state by
          beating or pressure...

       2. A mixture of meal or bran and water fed to animals.

       3. A mess; trouble.  [Obs.]  -Beau. & Fl.

   M4sh reserves the M4 macro namespace ‘^_AS_’ for internal use, and
the namespace ‘^AS_’ for M4sh macros.  It also reserves the shell and
environment variable namespace ‘^as_’, and the here-document delimiter
namespace ‘^_AS[A-Z]’ in the output file.  You should not define your
own macros or output shell code that conflicts with these namespaces.

* Menu:

* Common Shell Constructs::     Portability layer for common shell constructs
* Polymorphic Variables::       Support for indirect variable names
* Initialization Macros::       Macros to establish a sane shell environment
* File Descriptor Macros::      File descriptor macros for input and output