cmdline.c

#include <stdio.h>
#include <string.h>
#include <unistd.h>

void print_cmdline(void);

int main(int argc, char **argv) {
    char *end;
    print_cmdline();
    end = argv[argc-1] + strlen(argv[argc-1]);
    memset(*argv, 'X', end-*argv);
    print_cmdline();
    return 0;
}

void print_cmdline() {
    FILE* fd = fopen("/proc/self/cmdline", "r");
    char buf[1024];
    size_t len = fread(buf, 1, 1023, fd);
    buf[len] = '\n';
    fwrite(buf, len+1, 1, stdout);
    fflush(stdout);
}