A simple C program that adds remove-on-copy support to "tar c | tar x" command

tar_remove_on_copy.c

/*
  remove_on_copy.c: Remove each file listed in tar archive once they sent to stdout

  Usage:
     stdin: Tar archive (only ustar format is supported) created by tar -c
    stdout: Tar extract command (tar -x)

  Option:
    -v      Enable verbose output

  Example usage:
    tar -c . | ./remove_on_copy | tar -xp -C /
    # equivalent to:
    # rsync --remove-source-files . /

  This file can be built with:
    gcc remove_on_copy.c -lm -o remove_on_copy
*/

#include <stdbool.h>
#include <stdlib.h>
#include <stdio.h>
#include <string.h>
#include <unistd.h>
#include <math.h>

bool verbose = false;

int main (int argc, char * argv[]) {
  int exitstatus = 0;
  if ( argc > 1 && strcmp(argv[1], "-v") == 0 ) verbose = true;

  // process each file in archive
  while (true) {
    char name[100], octal_size[12], type[1];

    // filename (first 100 byte)
    {
      read(STDIN_FILENO, name, 100);

      if (name[0] == '\0') {
        // exit if filename is empty (extra empty blocks created by tar)
        break;
      } else {
        // write it back to stdout
        write(STDOUT_FILENO, name, 100);
      }
    }

    // metadata between filename and file size (24 bytes)
    {
      // read it from stdin and pass it to stdout
      char buf[24];
      read(STDIN_FILENO, buf, 24);
      write(STDOUT_FILENO, buf, 24);
    }

    // file size in octal (12 bytes)
    {
      read(STDIN_FILENO, octal_size, 12);
      write(STDOUT_FILENO, octal_size, 12);
    }

    // metadata between file size and type flag (20 bytes)
    {
      char buf[20];
      read(STDIN_FILENO, buf, 20);
      write(STDOUT_FILENO, buf, 20);
    }

    // type flag (1 byte)
    {
      read(STDIN_FILENO, type, 1);
      write(STDOUT_FILENO, type, 1);
    }

    // remaining metadata (355 bytes)
    {
      char buf[355];
      read(STDIN_FILENO, buf, 355);
      write(STDOUT_FILENO, buf, 355);
    }

    // 100 + 24 + 12 + 20 + 1 + 355 = 512, end of file meta

    // calculate number of blocks taken by the file, write all blocks
    // to stdout (contain contents of the file)
    int  size = strtol(octal_size, NULL, 8),
        block = ceil(size / 512.0);

    //if (verbose == true) fprintf(stderr, "[tar_remove_on_copy]: \e[0;33mname: %s, type: %c, size: %dB\e[0m\n", name, type[0], size);

    for (int i=0; i < block; i++) {
      // each block takes 512 bytes
      char buf[512];
      read(STDIN_FILENO, buf, 512);
      write(STDOUT_FILENO, buf, 512);
    }

    // ignore directory, remove file only
    if (type[0] != '5') {
      // remove the file
      if ( remove(name) == 0 ) {
        if (verbose == true) fprintf(stderr, "[tar_remove_on_copy]: \e[1;32mFile removed: %s\e[0m\n", name);
      } else {
        fprintf(stderr, "[tar_remove_on_copy]: \e[1;31m%s%s\e[0m\n", "Failed to remove file: ", name);
        exitstatus = 1;
      }
    }

    fflush(stderr);
  }

  return exitstatus;
}