> On Aug 12, 2016, at 2:41 PM, rain1_AT_openmailbox.org wrote:
>
> Hello!
>
> GNU Bash is 138227 lines of code. I wrote a simpler shell* in 800 lines: https://notabug.org/rain1/s/
>
> *It is not a true POSIX shell. You can't run existing scripts with it. It's technically just a command interpreter.
>
> With that out the way here's an overview of how it works:
>
> Tokenization [tokenizer.c]: Instead of the strange and complex way that normal shells work (where "$X" is different to $X for example) s works by a strict tokenize -> variable expansion -> parse -> execute pipeline. This makes it much easier to program with and less likely for scripts to break simply because your CWD has a space in it.
>
> Variable expansion [variables.c]: The expander supports both $FOO and ${FOO} syntax, it just resolves environment variables.
>
> Parsing [parser.c]: There are just 3 binary operations |, && and || and '&' optional at the end of a line. There is no "if" or looping or anything. parser.c is 85 lines of code and uses my region [region.c] based allocator to simplify teardown of the structure when it needs to be free'd.
>
> [interpreter.c] The interpreter is a simple recursive process that walks the AST, creating pipes and forking off children.
>
> [supporting/*.c] Instead of redirection operators like <, > and >> being part of the language they are simply provided as supporting programs that should be added to the $PATH: < is basically just cat. The redirection operators are all packaged together in busybox style. Similarly glob is not part of the language, it is a 20 line script instead. You use it like this: glob rm *py
>
> [builtins.c] Of course a shell cannot do everything by external tools - so the builtins cd, source, set, unset are provided (and treated specially by the interpreter).
>
> It can run scripts you supply, shebang works, using it in a terminal interactively works. In theory enough for practical every day use.
>
> Except for the low linecount (it is even smaller than execline) and simplicity of the lexical aspect of the shell language it does not have strong benefits over existing shells (especially since it is not POSIX compatible) but I hope that the code may be interesting or refreshing to others who are unhappy with the excess of bloat most software has.
>
>
I think it's pretty cool. There are some interesting shortcuts, like the redirection and glob not as built-ins, and trying to be just a shell and not a scripting language. It also seems to have a consistent ideology behind it, in a good sense.
Received on Sat Aug 13 2016 - 08:31:19 CEST