getflags: import from 4e, with usage

fixes #6 http://bitbucket.org/rsc/plan9port/issue/6/

http://codereview.appspot.com/95043

cmd/getflags.c

@@ -0,0 +1,82 @@
+#include <u.h>
+#include <libc.h>
+
+void
+usage(void)
+{
+	print("status=usage\n");
+	exits(0);
+}
+
+char*
+findarg(char *flags, Rune r)
+{
+	char *p;
+	Rune rr;
+	
+	for(p=flags; p!=(char*)1; p=strchr(p, ',')+1){
+		chartorune(&rr, p);
+		if(rr == r)
+			return p;
+	}
+	return nil;	
+}
+
+int
+countargs(char *p)
+{
+	int n;
+
+	n = 1;
+	while(*p == ' ')
+		p++;
+	for(; *p && *p != ','; p++)
+		if(*p == ' ' && *(p-1) != ' ')
+			n++;
+	return n;
+}
+
+void
+main(int argc, char *argv[])
+{
+	char *flags, *p, buf[512];
+	int i, n;
+	Fmt fmt;
+	
+	quotefmtinstall();
+	argv0 = argv[0];	/* for sysfatal */
+	
+	flags = getenv("flagfmt");
+	if(flags == nil){
+		fprint(2, "$flagfmt not set\n");
+		print("exit 'missing flagfmt'");
+		exits(0);
+	}
+
+	fmtfdinit(&fmt, 1, buf, sizeof buf);
+	for(p=flags; p!=(char*)1; p=strchr(p, ',')+1)
+		fmtprint(&fmt, "flag%.1s=()\n", p);
+	ARGBEGIN{
+	default:
+		if((p = findarg(flags, ARGC())) == nil)
+			usage();
+		p += runelen(ARGC());
+		if(*p == ',' || *p == 0){
+			fmtprint(&fmt, "flag%C=1\n", ARGC());
+			break;
+		}
+		n = countargs(p);
+		fmtprint(&fmt, "flag%C=(", ARGC());
+		for(i=0; i<n; i++)
+			fmtprint(&fmt, "%s%q", i ? " " : "", EARGF(usage()));
+		fmtprint(&fmt, ")\n");
+	}ARGEND
+	
+	fmtprint(&fmt, "*=(");
+	for(i=0; i<argc; i++)
+		fmtprint(&fmt, "%s%q", i ? " " : "", argv[i]);
+	fmtprint(&fmt, ")\n");
+	fmtprint(&fmt, "status=''\n");
+	fmtfdflush(&fmt);
+	exits(0);
+}