[GRASS-dev] g.mlist as C implementation?

[Glynn Clements]

Hamish wrote:

> I noticed parts of the script may be a bit fragile/inefficient, which is
> of concern for a module mainly intended as a scripting tool.
> 
> - The script relies on "echo -n"; not portable?

Nope. According to the official specification, echo doesn't accept any
switches. OTOH, the GNU version doesn't support the \c sequence. IOW,
there is no portable way to echo a string without appending a newline.

>   http://www.opengroup.org/onlinepubs/009695399/utilities/echo.html
> 
> 
> +    g.list type=$type mapset=$mapset \
> +	| grep -v '^-\+$' \
> +	| grep -v "files available" \
> +	| grep -vi "mapset" \
> +	| sed 's/  */\n/g' \
> +	| grep -v '^$' \
> +	| grep "$search" \
> +	| sort \
> +	| while read i
> 
> - combine the groups of sequential greps into single calls with the \|
>   "OR" expr.

The second and third can certainly be combined that way, provided that
you can use (or not use) -i for both (which is probably the case). I'm
not sure whether you can include the anchors (^ and $) within a
branch.

Hmm; this is wrong:

	grep -vi "mapset"

Nothing (other than common sense) prevents you from creating a map
named "mapset".

> - The `grep -v "files available"` will fail when translated,
>     'raster files available in mapset <PERMANENT>:'
>   I assume the `grep -vi "mapset"` is there as a poor workaround for that.
>   ("mapset" will not be as translated as often as "files available") :-/

One more reason why we need a g.list which isn't quite so "hostile" to
scripting.

> Is there a standard C library fn we can call to get regex support?
> Direct pattern searching in g.list would be preferable; I agree that
> a DIY reimplementation is a lot more trouble than it is worth. (unless
> some standard GPL code is copied verbatim into a new G_regex() libgis fn)?
> things like r.out.mpeg have basic map-name matching capabilities already.

For regular expressions, regcomp(), regexec(), regfree() and
regerror() are specified by POSIX.1. For shell "glob" patterns,
fnmatch() is specified by POSIX.2. None of these are specified by
either version of ANSI C, so we would need additional libraries for
Windows.

-- 
Glynn Clements <glynn at gclements.plus.com>