awk output to many files

[Henry Spencer]

As has been noted in the past, awk(1) has an annoying limitation on the
number of files it can send output to.  It's hard to get around this,
since the file opens are implicit and there is no way to explicitly
close a file that is no longer needed.  However, it's possible, and
not even very hard, to eliminate this problem in one particular case.
When the file is being used for appending (">>" redirection), then
closing it and re-opening it is a no-op.  The following changes to
awk will let it re-use append-mode file descriptors when it runs low
on descriptors.  There's a substantial performance loss, of course,
but it occurs only when you are genuinely using more files than awk
would normally permit.

All these changes are in awk/run.c.  Line numbers should be considered
approximate only.  Add the following new member to the "files" struct:

	13a14
	> 	int appending;

Add the following new declaration to the local variables in the function
redirprint():

	844a846
	> 	int app;

Make the following changes to code early in redirprint():

	852,856c854,867
	< 	for (i=0; i<FILENUM; i++)
	< 		if (files[i].fp == 0)
	< 			break;
	< 	if (i >= FILENUM)
	< 		error(FATAL, "too many output files %d", i);
	---
	> 	app = -1;
	> 	for (i=0; i<FILENUM && files[i].fp != 0; i++)
	> 		if (files[i].appending)
	> 			app = i;
	> 	if (i >= FILENUM && app == -1)
	> 		error(FATAL, "too many output files %d", i);
	> 	if (i >= FILENUM) {	/* but there is an append we can close */
	> 		fclose(files[app].fp);
	> 		files[app].fp = 0;
	> 		free(files[app].fname);
	> 		files[app].fname = 0;
	> 		files[app].appending = 0;
	> 		i = app;
	> 	}

And, slightly further down in redirprint(), add the following line just
after the "files[i].fname = tostring(x.optr->sval);" line:

	865a877
	> 	files[i].appending = (a == APPEND) ? 1 : 0;

Note that this code makes no attempt to intelligently choose *which*
append-mode file descriptor to close; it probably ought to use LRU or
something like that.
-- 
				Henry Spencer @ U of Toronto Zoology
				{allegra,ihnp4,linus,decvax}!utzoo!henry