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Forth-like routines for UNIX/Linux shell

summary

    This subchapter looks at a set of Forth-like routines for use in the BASH UNIX (Linux, Mac OS X) shell.

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Forth-like routines for UNIX/Linux shell

    This subchapter looks at a set of Forth-like routines for use in the BASH UNIX (Linux, Mac OS X) shell.

basic approach

    This supplementary material describes a method for creating Forth-like routines for use in the BASH shell.

    The data and return stacks will be stored using a pair of shell variables, one of which is an array and the other is an ordinary scalar variable.

    The Forth-like routines will be created as shell functions.

    Everything will be stored in a shell function file that can be loaded manually or loaded as part of the normal shell start-up.

    Eventually I intend to write two sets of C source code, one that people can commpile into their own copy of the official BASH source code and one that is part of an entirely new open source shell project that doesn’t have the GNU infecting license. This alternative shell will be designed so that it can run on bare metal, allowing it to be used to deploy embedded systems.

stacks

    Forth uses two stacks: the main data stack and the return stack.

    For the purposes of the BASH shell, we will implement both stacks with a combination of a top of stack pointer variable and an array for the stack. The top of stack pointer will hold the array index of the top of the stack. The stack will build up from the array indexed as one. An empty stack is indicated by having the top of stack pointer variable point to the zero index of the stack array variable. The bottom of the stack will actually be the one index of the stack array variable.

    $ export DataStackPointer=0
    $ declare -a DataStack='zero'; export DataStack
    $ export ReturnStackPointer=0
    $ declare -a ReturnStack='zero'; export ReturnStack
    $

    That’s it for the required variables! And, yes, those could all be placed on one line, but I spread them over four lines for additional clarity.

functions

    These are the functions for a Forth-like working environment. Not all of these functions exist in a real Forth. Most of these functions are have modifications from standard Forth. Many standard Forth functions are missing.

    In particular, this approach treats the stack as a stack of objects. No matter how much memory space an object takes up, it only takes up a single stack slot. In a real Forth, data is stored on the stack as raw binary strings, characters, or numbers and the programmer is responsble for keeping track of how much memory every item actually uses.

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