mush - the Memory Unsafe SHell

mush.c

/**
 * mush - the Memory Unsafe SHell
 * a crappy shell written in dirty C
 * 
 * A couple words from the dev:
 *   "I hate this"
 *   "it can run commands"
 *   "wow this thing can't even cd"
 **/

#include <linux/limits.h>
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <sys/types.h>
#include <sys/wait.h>
#include <pwd.h>
#include <string.h>
#include <limits.h>
#include <errno.h>

int main(void) {
    for (;;) {
        // fetch and display prompt infos
        char* username = getpwuid(getuid())->pw_name;
        char hostname[HOST_NAME_MAX];
        gethostname(hostname, HOST_NAME_MAX);
        char cwd[PATH_MAX];
        getcwd(cwd, PATH_MAX);
        printf("%s@%s %s $ ", username, hostname, cwd);
        
        // grab all input up to \n
        char input[513];
        scanf("%512[^\n]", input);
        while (getchar() != '\n');

        // split '&&' chained commands
        int cmds_count = 0;
        char** cmds = NULL;
        char* cmd = strtok(input, "&&");
        while (cmd != NULL) {
            cmds = reallocarray(cmds, cmds_count+1, sizeof(*cmds));
            if (cmds == NULL) {
                exit(EXIT_FAILURE);
            }
            cmds[cmds_count++] = cmd;
            cmd = strtok(NULL, "&&");
        }

        // run all commands until either finished or one failed
        for (int i = 0; i < cmds_count; i++) {
            // split cmd into argv for execvp
            int exec_argc = 0;
            char** exec_argv = NULL;
            char* arg = strtok(cmds[i], " ");
            while (arg != NULL) {
                exec_argv = reallocarray(exec_argv, exec_argc+1, sizeof(*exec_argv));
                if (exec_argv == NULL) {
                    exit(EXIT_FAILURE);
                }
                exec_argv[exec_argc++] = arg;
                arg = strtok(NULL, " ");
            }
            // NULL terminate argv
            exec_argv[exec_argc] = NULL;

            // fork to execute cmd
            pid_t cmd_pid = fork();
            switch(cmd_pid) {
                case -1:
                    perror("fork failed");
                    exit(EXIT_FAILURE);
                case 0:
                    execvp(exec_argv[0], exec_argv);
                    // exit with code 127 in case execvp fails
                    // mimics bash's "command not found"
                    perror("exec failed");
                    exit(127);
            }
            
            // wait for forked command
            int cmd_status;
            waitpid(cmd_pid, &cmd_status, 0);

            // print exit code
            int exit_code = WEXITSTATUS(cmd_status);
            printf("Exit Code: %d\n", exit_code);

            // stop if last command exited with error
            if (exit_code != 0) {
                break;
            }
        }
    }
    // if we somehow break from the loop exit with failure
    exit(EXIT_FAILURE);
}