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#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
**
** License: 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);
}
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