Print list of ALL environment variables

Question

I would like to print a list of all environment variables and their values. I searched the Stackoverflow and the following questions come close but don't answer me:

How to discover what is available in lua environment? (it's about Lua environment not the system environment variables)
Print all local variables accessible to the current scope in Lua (again about _G not the os environment variables)
http://www.lua.org/manual/5.1/manual.html#pdf-os.getenv (this is a good function but I have to know the name of the environment variable in order to call it)

Unlike C, Lua doesn't have envp** parameter that's passed to main() so I couldn't find a way to get a list of all environment variables. Does anybody know how I can get the list of the name and value of all environment variables?

score 5 · Answer 1 · answered Oct 03 '11 at 09:54

5

Standard Lua functions are based on C-standard functions, and there is no C-standard function to get all the environment variables. Therefore, there is no Lua standard function to do it either.

You will have to use a module like luaex, which provides this functionality.

answered Oct 03 '11 at 09:54

Nicol Bolas

449,505
63
781
982

4

@AlexStack: Not quite. `argv` refers to the command-line arguments passed to the program. `envp` refers to environment variables, but it's non-standard. – Keith Thompson Mar 04 '13 at 18:39

score 2 · Answer 2 · answered Aug 13 '13 at 16:13

You can install the lua-posix module. Alternatively, RedHat installations have POSIX routines built-in, but to enable them, you have to do a trick:

  cd /usr/lib64/lua/5.1/
  # (replace 5.1 with your version)
  ln -s ../../librpmio.so.1 posix.so
  # (replace the "1" as needed)
  lua -lposix
  > for i, s in pairs(posix.getenv()) do print(i,s,"\n") end

The trick is in creating a soft-link to the RPM's "io" directory and to naming the soft-link the same name of the library LUA will attempt to open. If you don't do this, you get:

./librpmio.so: undefined symbol: luaopen_librpmio

or similar.

score 2 · Answer 3 · answered Apr 18 '15 at 11:35

2

local osEnv = {}

for line in io.popen("set"):lines() do 
  envName = line:match("^[^=]+")
  osEnv[envName] = os.getenv(envName)
end

this would not work in some cases, like "no valid shell for the user running your app"

answered Apr 18 '15 at 11:35

Daniel Podolsky

81
3

1

It could also fail if some environment variable names or values contain newlines or other funny characters. – Keith Thompson Oct 14 '15 at 22:47

score 2 · Accepted Answer · answered Oct 04 '11 at 13:30

This code was extracted from an old POSIX binding.

static int Pgetenv(lua_State *L)        /** getenv([name]) */
{
    if (lua_isnone(L, 1))
    {
        extern char **environ;
        char **e;
        if (*environ==NULL) lua_pushnil(L); else lua_newtable(L);
        for (e=environ; *e!=NULL; e++)
        {
            char *s=*e;
            char *eq=strchr(s, '=');
            if (eq==NULL)       /* will this ever happen? */
            {
                lua_pushstring(L,s);
                lua_pushboolean(L,0);
            }
            else
            {
                lua_pushlstring(L,s,eq-s);
                lua_pushstring(L,eq+1);
            }
            lua_settable(L,-3);
        }
    }
    else
        lua_pushstring(L, getenv(luaL_checkstring(L, 1)));
    return 1;
}

well, this is one way to solve the problem using C. Apparently there's no pure-Lua function that does this. Thanks anyway. — AlexStack, Oct 07 '11 at 14:24
@AlexStack, as mentioned by Nicol, there is no pure-Lua function because `environ` is not ANSI C, just POSIX. — lhf, Oct 07 '11 at 14:48

score 1 · Answer 5 · answered Jun 09 '21 at 20:15

1

An easy 2 liner:

    buf = io.popen("env", '*r')
    output = buf:read('*a')
    print(output) -- or do whatever

answered Jun 09 '21 at 20:15

Mysterion

11
1

Print list of ALL environment variables

5 Answers5