[GRASS-dev] erratic behavior of v.in.ascii with WinGRASS

[Glynn Clements]

Michael Barton wrote:

> > If the string is parsed by the shell, it needs to be quoted, otherwise
> > it doesn't.
> >
> >> Given these tests and what Glynn said (subsequent post), it seems
> >> safest to always quote or escape the | character in v.in.ascii. In
> >> this regard, is there a problem with making the default separator for
> >> the g.parser section of v.in.ascii "|" instead of the current | ?
> >
> > Yes. That would cause the quotes to be treated as part of the argument
> > to the fs= option.
> 
> I don't understand. Helena suggested that I put quotes around "|",  
> which I did and which worked--from the GUI. So why not make this the  
> default

Because the quotes will become part of the value of the fs= option, so
both the double quote character and the vertical bar character will be
treated as field separators. That will be a problem if you have any
double quote characters within the data.

If you want to pass | as the argument to fs=, pass |, don't pass a
string containing both | and ".

> >> As an aside, the | character seems like an odd default separator for
> >> data fields in GRASS. I suppose it's a holdover from the ancient
> >> past. But the fact that this is also has meaning as a pipe seems to
> >> make it a risky separator in general. What about switching this to
> >> something else in GRASS 7?
> >
> > There's only thing that's "risky" about using "|" is that certain bugs
> > in code which executes commands will show up rather than getting
> > overlooked.
> >
> > If such bugs exist, they should be fixed, rather than having
> > individual cases worked around.
> 
> OK. But I don't understand what needs to be fixed here (though I'd be  
> happy to have whatever needs to be fixed, fixed). I'm hearing quote  
> the | character and don't quote the | character. So I'm confused.

To use the | character as the field separator, you want to ensure that
one element in the argv[] passed to v.in.ascii's main function is
exactly equal to "fs=".

How you do that depdends upon how you're invoking v.in.ascii. E.g. if
you're using the C execl() function:

	execl("v.in.ascii", "v.in.ascii", "fs=|", <other arguments>, NULL);

If you're using Tcl's "open":

	set h [open |v.in.ascii fs=| <other arguments>]

If you're using the shell:

	v.in.ascii fs='|' <other arguments>
or:
	v.in.ascii fs=\| <other arguments>
or:
	v.in.ascii "fs=|" <other arguments>

Python's subprocess.Popen():

	p = Popen(["v.in.ascii", "fs=|", <other arguments>])

And so on.

What matters is that you get a specific string to appear in some
member of argv[].

If you're not sure what's ending up in argv[], add some debugging
statements, or replace the target program with something like the
following:

	#include <stdio.h>
	int main(int argc, const char * const * const argv)
	{
		int i;
		for (i = 0; i < argc; i++)
			printf("argv[%2d]: %s\n", i, argv[i]);
		return 0;
	}

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