$ cat proc-self.c
#include <stdio.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>

char *cmdline_fname = "/proc/self/cmdline";

#define BUFSIZE 32

int main(void) {
        int cmdline_fd;
        char cmdline[BUFSIZE];

        cmdline_fd = open(cmdline_fname, O_RDONLY);
        if (cmdline_fd != -1) {
                if (read(cmdline_fd, cmdline, BUFSIZE) != -1) {
                        printf("%s\n", cmdline);
                }
                close(cmdline_fd);
        }
}
$ gcc -o proc-self{,.c}
$ ./proc-self df lkjf lk
./proc-self