--- /dev/null
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <sys/types.h>
+#include <sys/stat.h>
+#include <fcntl.h>
+#include <unistd.h>
+#include <errno.h>
+
+/**
+ ** grok -- program to a alter bytes at an offset
+ **
+ ** Sometimes it useful to alter bytes in a binary file.
+ ** To those who would 'just use emacs', the binary is not always a file on disk.
+ **
+ ** codedr@gmail.com
+ **
+ ** Licence: Public Domain
+ */
+
+int
+main(int argc, char **argv)
+{
+ int i, dc = 0, fd;
+ int sz, cnt, offset;
+ char *fn;
+ unsigned char *buf, *data;
+ /* grok fn offset data */
+
+ if (3 > argc) {
+ fputs("usage: grok fn offset [cdata]+\n", stderr);
+ exit(1);
+ }
+ fn = argv[1];
+ offset = strtol(argv[2], NULL, 16);
+ data = (unsigned char *) calloc(argc - 2, sizeof(unsigned char));
+ for (i = 3; i < argc; i++) {
+ long x;
+ x = strtol(argv[i], NULL, 16);
+ data[dc++] = 0xff & x;
+ }
+
+ if (0 > (fd = open(fn, O_RDWR))) {
+ fprintf(stderr, "cannot open %s, errno %d\n", fn, errno);
+ exit(2);
+ }
+
+ if (0 > lseek(fd, offset, SEEK_SET)) {
+ fprintf(stderr, "cannot seek to %x, errno %d\n", offset, errno);
+ exit(2);
+ }
+
+ buf = (unsigned char *) calloc(dc, sizeof(unsigned char));
+
+ if (0 > (cnt = read(fd, buf, dc))) {
+ fprintf(stderr, "cannot read %d bytes at %x, errno %d\n",
+ dc, offset, errno);
+ exit(3);
+ }
+ printf("read %d of %d bytes\n", cnt, dc);
+ /* dumpBuf(buf, cnt); */
+
+ if (0 > lseek(fd, offset, SEEK_SET)) {
+ fprintf(stderr, "cannot seek to %x, errno %d\n", offset, errno);
+ exit(2);
+ }
+
+ if (0 > (sz = write(fd, data, cnt))) {
+ fprintf(stderr, "cannot write %d bytes at %x, errno %d\n",
+ cnt, offset, errno);
+ exit(4);
+ }
+ printf("wrote %d of %d bytes\n", sz, cnt);
+ exit(0);
+}