Fix Tarantool's start in background

$ TT_PID_FILE=tarantool.pid TT_LOG=tarantool.log TT_BACKGROUND=true TT_LISTEN=3301 tarantool -e 'box.cfg{}'
$ tail -3 tarantool.log
2021-11-02 16:05:43.672 [2341202] main init.c:696 E> LuajitError: cannot read stdin: Resource temporarily unavailable
2021-11-02 16:05:43.672 [2341202] main F> fatal error, exiting the event loop
2021-11-02 16:05:43.672 [2341202] main F> fatal error, exiting the event loop
$

commit 1b33012 (origin/gh-5999)
Author: Roman Khabibov <roman.habibov@tarantool.org>
Date:   Tue Mar 9 16:47:11 2021 +0300

    box: set box.cfg options via environment variables

commit 9db64ae
Author: Roman Tsisyk <roman@tarantool.org>
Date:   Thu Aug 17 16:59:16 2017 +0300

    lua: add '-' command line option

Closes #6128

src/lua/init.c

@@ -36,6 +36,7 @@
 #endif
 
 #include <lua.h>
+#include <stdio.h>
 #include <lauxlib.h>
 #include <lualib.h>
 #include <lj_cdata.h>
@@ -45,6 +46,8 @@
 #include "version.h"
 #include "backtrace.h"
 #include "coio.h"
+#include <stdio.h>
+#include "cfg.h"
 #include "lua/fiber.h"
 #include "lua/fiber_cond.h"
 #include "lua/fiber_channel.h"
@@ -647,6 +650,17 @@ run_script_f(va_list ap)
 		is_a_tty = inj->iparam;
 	});
 
+        /*
+	int background = 0;
+	lua_getglobal(L, "box");
+        if (lua_isnil(L, -1)) {
+            lua_getfield(L, -1, "cfg");
+            if (lua_istable(L, -1)) {
+                    background = cfg_geti("background");
+            }
+        }
+        */
+
 	if (path && strcmp(path, "-") != 0 && access(path, F_OK) == 0) {
 		/* Execute script. */
 		if (luaL_loadfile(L, path) != 0)
@@ -659,6 +673,12 @@ run_script_f(va_list ap)
 			goto luajit_error;
 		if (lua_main(L, argc, argv) != 0)
 			goto error;
+	} else if (is_option_e_ran) {
+                /* Execute a string passed with option -e */
+		if (luaL_loadstring(L, "print()") != 0)
+			goto luajit_error;
+		if (lua_main(L, argc, argv) != 0)
+			goto error;
 	} else if (!is_option_e_ran) {
 		interactive = true;
 	}

test/box-tap/gh-5602-environment-cfg-test-cases.lua

@@ -67,5 +67,13 @@ if arg[1] == '5' then
     end
     test:is(err_msg, exp_err, 'bad strip_core value')
 end
+if arg[1] == '6' then
+    test:plan(5)
+    test:ok(status, 'box.cfg is successful')
+    test:is(box.cfg['listen'], '3301', 'listen')
+    test:is(box.cfg['background'], true, 'background')
+    test:is(box.cfg['pid_file'], 'tarantool.pid', 'pid file')
+    test:is(box.cfg['log'], 'tarantool.log', 'log file')
+end
 
 os.exit(test:check() and 0 or 1)

test/box-tap/gh-5602-environment-vars-cfg.test.lua

@@ -39,6 +39,11 @@ local cases = {
     'TT_BACKGROUND=true TT_VINYL_TIMEOUT=60.1',
     'TT_SQL_CACHE_SIZE=a',
     'TT_STRIP_CORE=a',
+    ('%s %s %s %s'):format(
+        'TT_LISTEN=3301',
+        'TT_LOG=tarantool.log',
+        'TT_PID_FILE=tarantool.pid',
+        'TT_BACKGROUND=true'),
 }
 
 test:plan(1)