cleaned up version of https://gist.github.com/samdmarshall/8edb5e246fcbb09ce6e7

c4pture

//
//  main.c
//  c4pture
//
//  Created by Sam Marshall on 12/22/13.
//  Copyright (c) 2013 Sam Marshall. All rights reserved.
//

#include <stdio.h>
#include <stdint.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <sys/fcntl.h>
#include <unistd.h>
#include <errno.h>
#include <string.h>
#include <stdlib.h>

#define TAIG_START 0x8faeac
#define TAIG_LENGTH 0xd134f5
#define CYDIA_START 0x1a842d
#define CYDIA_LENGTH 0x6d24ff

size_t replace_bytes(int fd, uint32_t srcStart, uint32_t srcLen, uint32_t destStart, uint32_t destLen);

int main(int argc, const char *argv[]) {
    int status = 0x0;

    if (argc != 0x2 || strcmp(argv[1], "--help") == 0)
    {
        printf("usage: %s <evasi0n executable path>\n", argv[0]);
        return 0x1;
    }

    struct stat fs;
    char *path = (char *)argv[0x1];
    int statResult = stat(path, &fs);
    if (statResult != 0x0)
    {
        printf("error: file %s not found\n", argv[1]);
        return 0x1;
    }

    int fd = open(path, O_RDWR);

    size_t length = replace_bytes(fd, CYDIA_START, CYDIA_LENGTH, TAIG_START, TAIG_LENGTH);

    if (length == -1) {
        printf("error: (%i) %s\n",errno,strerror(errno));
        status = 0x1;
    } else {
        printf("successfully patched evasi0n7!\n");
    }
    close(fd);

    return status;
}

size_t replace_bytes(int fd, uint32_t srcStart, uint32_t srcLen, uint32_t destStart, uint32_t destLen)
{
    if(srcLen > destLen)
    {
        printf("error: replace_bytes: srcLen > destLen\n");
        exit(1);
        return -1;
    }
    //zero out the place you want to copy to
    lseek(fd, destStart, SEEK_SET);
    uint32_t *zero = calloc(0x1, destLen);
    write(fd, zero, destLen);

    //get data to copy
    lseek(fd, srcStart, SEEK_SET);
    char *buffer = calloc(0x1, srcLen);
    read(fd, buffer, srcLen);

    //replace that shit
    lseek(fd, destStart, SEEK_SET);
    size_t length = write(fd, buffer, srcLen);

    free(zero);
    free(buffer);

    return length;
}