basic shell

main.c

@@ -0,0 +1,117 @@
+#include <stdlib.h>
+#include <string.h>
+#include <unistd.h>
+#include <stdint.h>
+#include <stdio.h>
+#include <readline/readline.h>
+#include <sys/wait.h>
+#include <signal.h>
+#include <setjmp.h>
+
+static sigjmp_buf restart_jmp_buf;
+static const int restart_value = 69;
+static volatile sig_atomic_t jump_active = 0;
+
+void sigint_handler(int signo)
+{
+  if(!jump_active)
+  {
+    return;
+  }
+  siglongjmp(restart_jmp_buf, restart_value);
+}
+
+char** split_input(char* input)
+{
+  const size_t alloc_size = ((strlen(input) + 1) / 2) + 1;
+  char** command = malloc(alloc_size * sizeof(char*));
+  if (command == NULL)
+  {
+    perror("malloc failed");
+    exit(1);
+  }
+  const char* separator = " ";
+  char* parsed;
+  uint32_t index = 0;
+  parsed = strtok(input, separator);
+  while (parsed != NULL)
+  {
+    command[index] = parsed;
+    index++;
+    parsed = strtok(NULL, separator);
+  }
+  command[index] = NULL;
+  return command;
+}
+
+int cd(char* path)
+{
+  return chdir(path);
+}
+
+int main()
+{
+  struct sigaction s;
+  s.sa_handler = sigint_handler;
+  sigemptyset(&s.sa_mask);
+  s.sa_flags = SA_RESTART;
+  struct sigaction s_old;
+  sigaction(SIGINT, &s, &s_old);
+
+  int stat_loc;
+
+  if(sigsetjmp(restart_jmp_buf, 1) == restart_value)
+  {
+    printf("\n");
+  }
+  jump_active = 1;
+  
+  while(true)
+  {
+    char* input = readline("arsh> ");
+    if(input == NULL) //CTRL + D
+    {
+      continue;
+    }
+    char** command = split_input(input);
+    
+    if(strcmp(command[0], "cd") == 0)
+    {
+      if (cd(command[1]) < 0)
+      {
+	perror(command[1]);
+      }
+
+      continue; //skip fork()
+    }
+    if(strcmp(command[0], "exit") == 0)
+    {
+      int32_t status_code = command[1] != NULL ? atoi(command[1]) : 0;
+      exit(status_code);
+    }
+    
+    pid_t child_pid = fork();
+    if (child_pid < 0) 
+    {
+      perror("Fork failed");
+      exit(1);
+    }
+    if (child_pid == 0)
+    {
+      sigaction(SIGINT, &s_old, NULL);
+      //never returns if call is successful
+      if(execvp(command[0], command) < 0)
+      {
+	perror(command[0]);
+	exit(1);
+      }
+    }
+    else
+    {
+      waitpid(child_pid, &stat_loc, WUNTRACED);
+    }
+
+    free(input);
+    free(command);
+  }
+}