Tool to unroll nested parameter expansions

Tool to unroll nested parameter expansions

[Felix Rosencrantz]

Anyone have a tool that can take a nested parameter expression (e.g. 
pats="${(@)${(@M)tmp1:#-g*}#-g}" ) , and break it down into simpler
substeps, so it is easier to read.

Some of the completion code uses complex parameter expansions, that
are difficult to read, and it would be useful if there was something
that could break it down into smaller more understandable steps, like
a line per ${} section.

-FR.

Re: Tool to unroll nested parameter expansions

[Bart Schaefer]

On Sat, 4 Dec 2004, Felix Rosencrantz wrote:

> Anyone have a tool that can take a nested parameter expression [...] and
> break it down into simpler substeps, so it is easier to read.

Unfortunately a tool to do this has to contain the equivalent of the 
entire shell parser, because a parameter expansion can contain $(...)
which can in turn contain arbitrary shell code (including other parameter
expansions, which would confuse any attempt to simplify the parse).

The "obvious" thing would be to instrument paramsubst() so you could see 
the dissection as the shell parses it (perhaps when both VERBOSE and 
XTRACE are set, or some such) but paramsubst() is already 1900 lines of 
subst.c, so that prospect is not appealing.