Thanks to John Cummings.

src/cmd/upas/bayes/addhash.c

@@ -0,0 +1,66 @@
+#include <u.h>
+#include <libc.h>
+#include <bio.h>
+#include <regexp.h>
+#include "hash.h"
+
+Hash hash;
+
+void
+usage(void)
+{
+	fprint(2, "addhash [-o out] file scale [file scale]...\n");
+	exits("usage");
+}
+
+void
+main(int argc, char **argv)
+{
+	int i, fd, n;
+	char err[ERRMAX], *out;
+	Biobuf *b, bout;
+
+	out = nil;
+	ARGBEGIN{
+	case 'o':
+		out = EARGF(usage());
+		break;
+	default:
+		usage();
+	}ARGEND;
+
+	if(argc==0 || argc%2)
+		usage();
+
+	while(argc > 0){
+		if((b = Bopenlock(argv[0], OREAD)) == nil)
+			sysfatal("open %s: %r", argv[0]);
+		n = atoi(argv[1]);
+		if(n == 0)
+			sysfatal("0 scale given");
+		Breadhash(b, &hash, n);
+		Bterm(b);
+		argv += 2;
+		argc -= 2;
+	}
+
+	fd = 1;
+	if(out){
+		for(i=0; i<120; i++){
+			if((fd = create(out, OWRITE, 0666|DMEXCL)) >= 0)
+				break;
+			rerrstr(err, sizeof err);
+			if(strstr(err, "file is locked")==nil && strstr(err, "exclusive lock")==nil)
+				break;
+			sleep(1000);
+		}
+		if(fd < 0)
+			sysfatal("could not open %s: %r\n", out);
+	}
+		
+	Binit(&bout, fd, OWRITE);
+	Bwritehash(&bout, &hash);
+	Bterm(&bout);
+	exits(0);
+}
+