Initial commit

.gitignore

@@ -0,0 +1,3 @@
+*.o
+vsh
+*~

Makefile

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+CC=gcc
+CFLAGS=-Wall -Werror -std=c99
+OBJS=argbuild.o vsh.o
+BINARY=vsh
+
+.PHONY: clean all debug release
+
+all: debug
+
+release: $(BINARY)
+
+debug:	CFLAGS += -g
+debug:	$(BINARY)
+
+$(BINARY): $(OBJS)
+	$(CC) -o $@ $(CFLAGS) $(OBJS) $(LDLIBS)
+
+%.o: %.c %.h
+	$(CC) -c $< -o $@ $(CFLAGS)
+
+clean:
+	rm $(OBJS) $(BINARY)

argbuild.c

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+#include "argbuild.h"
+
+#include <stdlib.h>
+#include <string.h>
+
+void add_arg(char* argument, arg_t* args){
+  arg_elt_t* toadd = malloc(sizeof(arg_elt_t));
+  toadd->arg = argument;
+  toadd->next = NULL;
+  if(args->end != NULL){
+    args->end->next = toadd;
+  }
+  args->end = toadd;
+  if(args->first == NULL){
+    args->first = toadd;
+  }
+  ++(args->argc);
+}
+
+arg_t* build_args(char* cmd, unsigned int cmd_max_len){
+  arg_t* to_return = malloc(sizeof(arg_t));
+  to_return->first = NULL;
+  to_return->end = NULL;
+  to_return->argc = 0;
+
+  int sub_start = 0;
+  int sub_end = 0;
+
+  for(unsigned int i = 0; i < cmd_max_len; ++i){
+    if(cmd[i] == '\0'){
+      break;
+    }
+    if(cmd[i] == ' ' || cmd[i] == '\n'){
+
+      //Ignore multiple spaces between arguments
+      if(cmd[i] == ' ' && cmd[i + 1] == ' '){
+	continue;
+      }
+
+      char delineate = cmd[i];
+
+      sub_end = i;
+      int new_str_siz = (sub_end - sub_start) + 1;
+
+      //Make sure the string is not empty
+      if(new_str_siz > 1){
+	//Temporarily add a null terminator in the cmd string to make
+	//strncpy's job easier
+	cmd[i] = '\0';
+	char* arg_str = malloc(sizeof(char) * new_str_siz);
+	//Copy the argument into the new string
+	strncpy(arg_str, &cmd[sub_start], new_str_siz);
+	//Add back in the space char that was replaced by null
+	//terminator
+	cmd[i] = delineate;
+	//Now add the string to our linked list of arg elts
+	add_arg(arg_str, to_return);
+	//Make sub_start point to the next char after cmd[i], which is
+	//a space
+	sub_start = i + 1;	
+      }
+    }
+  }
+
+  return to_return;
+}
+
+char** get_args(arg_t* args, int* numargs){
+  if(args->argc <= 0){
+    return NULL;
+  }
+
+  char** to_return = malloc(sizeof(char) * (args->argc + 1));
+  *numargs = 0;
+  for(arg_elt_t* it = args->first; it != NULL; it = it->next){
+    to_return[(*numargs)++] = it->arg;
+  }
+
+  //The last elt in this array is a null pointer
+  to_return[args->argc] = '\0';
+
+  return to_return;
+}
+
+void free_args(arg_t* tofree){
+  arg_elt_t* it = tofree->first;
+  while(it != NULL){
+    arg_elt_t* next = it->next;
+    if(it != NULL){
+      free(it->arg);
+    }
+    free(it);
+    it = next;
+  }
+  free(tofree);
+}

argbuild.h

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+#ifndef ARG_BUILD_H
+#define ARG_BUILD_H
+
+typedef struct arg_elt{
+  struct arg_elt* next;
+  char* arg;
+} arg_elt_t;
+
+typedef struct args{
+  arg_elt_t* first;
+  arg_elt_t* end;
+  int argc;
+} arg_t;
+
+arg_t* build_args(char* cmd, unsigned int cmd_max_len);
+char** get_args(arg_t* args, int* numargs);
+void free_args(arg_t* tofree);
+
+#endif

vsh.c

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+#include <stdio.h>
+#include <unistd.h>
+#include <stdlib.h>
+#include <sys/wait.h>
+#include <assert.h>
+
+#include "argbuild.h"
+
+#define DIR_STR_SIZ 1024
+
+int main(int argc, char** argv, char** envp){
+  char running = 1;
+  char pwd[DIR_STR_SIZ];
+  const long ARG_MAX = sysconf(_SC_ARG_MAX);
+  char cmdbuf[ARG_MAX];
+
+  char user_prompt = '$';
+  if(geteuid() == 0)
+    user_prompt = '#';
+
+  puts("Welcome to vsh, the Vukelich Shell.\n");
+
+
+  while(running){
+
+    //Get the current working directory.  If an error occurs, then
+    //set the pwd string to empty
+    if(getcwd(pwd, DIR_STR_SIZ) != pwd){
+      pwd[0] = '\0';
+    }
+
+    printf("%s %c ", pwd, user_prompt);
+
+    if(fgets(cmdbuf, ARG_MAX, stdin) != cmdbuf){
+      puts("\nExiting");
+      running = 0;
+      continue;
+    }
+
+    arg_t* args = build_args(cmdbuf, ARG_MAX);
+    int child_argc;
+    char** arg_ary = get_args(args, &child_argc);
+
+    if(!fork()){
+      execve(arg_ary[0], arg_ary, envp);
+      printf("%s: %s: Command not found\n", argv[0], arg_ary[0]);
+      return 1;
+    }
+    wait(NULL);
+    free(arg_ary);
+    free_args(args);
+
+  }
+
+  return 0;
+}