Issue

I wanna do some bitwise operations (for example xor two files) on files in Linux , and I have no idea how I can do that. Is there any command for that or not?

any help will be appreciated.

Solution

You can map the file with mmap, apply bitwise operations on the mapped memory, and close it.

Alternatively, reading chunks into a buffer, applying the operation on the buffer, and writing out the buffer works too.

Here's an example (C, not C++; since everything but the error handlings is the same) that inverts all bits:

#include <unistd.h>
#include <stdlib.h>
#include <stdio.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <sys/mman.h>
int main(int argc, char* argv[]) {
    if (argc != 2) {printf("Usage: %s file\n", argv[0]); exit(1);}

    int fd = open(argv[1], O_RDWR);
    if (fd == -1) {perror("Error opening file for writing"); exit(2);}

    struct stat st;
    if (fstat(fd, &st) == -1) {perror("Can't determine file size"); exit(3);}

    char* file = mmap(NULL, st.st_size, PROT_READ | PROT_WRITE,
                      MAP_SHARED, fd, 0);
    if (file == MAP_FAILED) {
        perror("Can't map file");
        exit(4);
    }

    for (ssize_t i = 0;i < st.st_size;i++) {
        /* Binary operation goes here.
        If speed is an issue, you may want to do it on a 32 or 64 bit value at
        once, and handle any remaining bytes in special code. */
        file[i] = ~file[i];
    }

    munmap(file, st.st_size);
    close(fd);
    return 0;
}

Answered By - phihag

Answer Checked By - Mary Flores (WPSolving Volunteer)

Wednesday, February 16, 2022

[SOLVED] How to perform bitwise operations on files in linux?

Issue

Solution