On Fri, Feb 18, 2011 at 9:35 PM, Greg Wooledge <wool...@eeg.ccf.org> wrote:
> On Fri, Feb 18, 2011 at 11:25:48AM +0800, Clark J. Wang wrote: > > A global var can always be declared out of a func (usually at the > beginning > > of the script) so what's the main intention of introducing a new `-g' > > option? > > The main reason, as I understand it, is so that you can declare an > associative array inside a function and have it be readable in the > caller. Unlike all other variables (strings, regular arrays), associative > arrays *must* be declared. But the declare builtin had the unfortunate > (for some purposes) side effect of also marking the variable as local. > > Prior to bash 4.2, any such associative array would have to be declared > outside the function. So, imagine a function like: > > # pqp - parse query parameters > # Input: QUERY_STRING environment variable > # Output: associative array 'qparams' containing CGI parameters as keys. > # (If a parameter is repeated, only the last instance is retained.) > > In bash < 4.2, the caller would have to pre-define the qparams associative > array, because the function cannot declare it at the global scope. > In bash 4.2, the function can create the array itself. Is that a huge > difference? Maybe not, but it's just more natural to do it the 4.2 way. > > Thanks for the kind explanation, Greg. I think the problem is that if people do not understand the feature requirement so they just cannot understand the feature well unless the feature works in a straightforward way. That's why I asked the question. > > And If we can declare/modify a global var in a func but we cannot read it > > from in the func I don't think the feature is very useful to people. > > Your example was interesting, but it was extremely convoluted. I tell > people over and over that writing big complicated shell scripts (or > worse, "reusable libraries" of shell code... *shudder*) is simply a > BAD idea. But nobody ever listens. > > Agree. I was offen depressed because of that. :) > In the normal case, when you write a shell script that only has one or > two functions in it, and there's no shadowing of global variables with > local variables by the same name, everything works as you expect. I'll > let you and Chet hammer out what to do in the more complex cases. > -- Clark J. Wang
