Our first junkcode!

junkcode/codedr@gmail.com-grok/grok.c

+#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);
+}