lush/lbuiltin.c

/*
** $Id: lbuiltin.c $
** Shell builtins (cd, exec, umask)
** See Copyright Notice in lua.h
*/

#define lbuiltin_c
#define LUA_LIB

#include <errno.h>
#include <stdlib.h>
#include <string.h>
#include <sys/stat.h>
#include <unistd.h>

#include "lua.h"
#include "lauxlib.h"
#include "lbuiltin.h"


static void push_builtin_result (lua_State *L, int code,
                                 const char *out, const char *err) {
  lua_createtable(L, 0, 3);
  lua_pushinteger(L, code);
  lua_setfield(L, -2, "code");
  lua_pushstring(L, out ? out : "");
  lua_setfield(L, -2, "stdout");
  lua_pushstring(L, err ? err : "");
  lua_setfield(L, -2, "stderr");
}


/*
** builtin_cd(cmd, [dir])
** Change working directory. No arg → $HOME, "-" → $OLDPWD.
** Updates $PWD and $OLDPWD.
*/
static int builtin_cd (lua_State *L) {
  const char *dir;
  char oldpwd[4096];
  char newpwd[4096];

  if (lua_gettop(L) < 2 || lua_isnil(L, 2)) {
    /* no dir argument: use $HOME */
    dir = getenv("HOME");
    if (dir == NULL) {
      push_builtin_result(L, 1, NULL, "cd: HOME not set");
      return 1;
    }
  }
  else {
    dir = luaL_checkstring(L, 2);
    if (strcmp(dir, "-") == 0) {
      dir = getenv("OLDPWD");
      if (dir == NULL) {
        push_builtin_result(L, 1, NULL, "cd: OLDPWD not set");
        return 1;
      }
    }
  }

  /* save current directory */
  if (getcwd(oldpwd, sizeof(oldpwd)) == NULL)
    oldpwd[0] = '\0';

  if (chdir(dir) != 0) {
    char errbuf[4200];
    snprintf(errbuf, sizeof(errbuf), "cd: %s: %s", dir, strerror(errno));
    push_builtin_result(L, 1, NULL, errbuf);
    return 1;
  }

  /* get resolved path */
  if (getcwd(newpwd, sizeof(newpwd)) == NULL)
    newpwd[0] = '\0';

  setenv("OLDPWD", oldpwd, 1);
  setenv("PWD", newpwd, 1);

  push_builtin_result(L, 0, NULL, NULL);
  return 1;
}


/*
** builtin_exec(cmd, program, [args...])
** Replace the shell process via execvp(2).
*/
static int builtin_exec (lua_State *L) {
  int nargs = lua_gettop(L);
  int i;
  char **argv;
  char errbuf[4200];

  if (nargs < 2) {
    push_builtin_result(L, 1, NULL, "exec: command required");
    return 1;
  }

  /* build argv from args 2..nargs (skip "exec" at arg 1) */
  argv = (char **)malloc((size_t)(nargs) * sizeof(char *));
  if (argv == NULL)
    return luaL_error(L, "out of memory");

  for (i = 2; i <= nargs; i++)
    argv[i - 2] = (char *)luaL_checkstring(L, i);
  argv[nargs - 1] = NULL;

  execvp(argv[0], argv);

  /* execvp only returns on failure */
  snprintf(errbuf, sizeof(errbuf), "exec: %s: %s", argv[0], strerror(errno));
  free(argv);
  push_builtin_result(L, 1, NULL, errbuf);
  return 1;
}


/*
** builtin_umask(cmd, [mode])
** No arg: query and print current umask. With arg: set umask from octal string.
*/
static int builtin_umask (lua_State *L) {
  if (lua_gettop(L) < 2 || lua_isnil(L, 2)) {
    /* query mode */
    mode_t old = umask(0);
    char buf[16];
    umask(old);  /* restore */
    snprintf(buf, sizeof(buf), "%04o\n", (unsigned)old);
    push_builtin_result(L, 0, buf, NULL);
    return 1;
  }
  else {
    const char *modestr = luaL_checkstring(L, 2);
    char *endp;
    unsigned long val;
    errno = 0;
    val = strtoul(modestr, &endp, 8);
    if (errno != 0 || *endp != '\0' || endp == modestr || val > 0777) {
      push_builtin_result(L, 1, NULL, "umask: invalid mode");
      return 1;
    }
    umask((mode_t)val);
    push_builtin_result(L, 0, NULL, NULL);
    return 1;
  }
}


void luaopen_builtins (lua_State *L) {
  lua_createtable(L, 0, 3);
  lua_pushcfunction(L, builtin_cd);
  lua_setfield(L, -2, "cd");
  lua_pushcfunction(L, builtin_exec);
  lua_setfield(L, -2, "exec");
  lua_pushcfunction(L, builtin_umask);
  lua_setfield(L, -2, "umask");
  lua_setglobal(L, "__builtins");
}