A simple program like a cat will trigger an oops. As I'm not able to get informations with the USB, I'm porividing the culprit to you.

#include "cat.h"
#include "builtins.h"

#include <stdio.h>

static void usage(char *execname)
{
    printf("usage : %s file\n", execname);
}


int builtin_cat(char **args)
{
    if (args[1] == NULL || args[2] != NULL) {
        usage(args[0]);
        return -1;
    }

    FILE* file = NULL
    file = fopen(args[1], "r");
    if(file == NULL) {
        perror("cat");
        return -1;
    }
    int c = 0;
    while(!feof(file) && !ferror(file) && ++c < 100)
        putchar(fgetc(file));
    if(ferror(file)) {
        perror("ls");
        fclose(file);
        return -1;
    }
    fclose(file);
    return 0;

}