Add env parameter to exec_sh()

Before passing the cmd to exec() we set the required environment
variables.

Also add the test for it.

include/utils/process.hpp

@@ -16,7 +16,7 @@ namespace process_util {
   void fork_detached(std::function<void()> const& lambda);
 
   void exec(char* cmd, char** args);
-  void exec_sh(const char* cmd);
+  void exec_sh(const char* cmd, const vector<pair<string, string>>& env = {});
 
   int wait(pid_t pid);
 

src/utils/process.cpp

@@ -124,9 +124,14 @@ namespace process_util {
   /**
    * Execute command using shell
    */
-  void exec_sh(const char* cmd) {
+  void exec_sh(const char* cmd, const vector<pair<string, string>>& env) {
     if (cmd != nullptr) {
       static const string shell{env_util::get("POLYBAR_SHELL", "/bin/sh")};
+
+      for (const auto& kv_pair : env) {
+        setenv(kv_pair.first.data(), kv_pair.second.data(), 1);
+      }
+
       execlp(shell.c_str(), shell.c_str(), "-c", cmd, nullptr);
       throw system_error("execlp() failed");
     }

tests/unit_tests/utils/process.cpp

@@ -32,3 +32,13 @@ TEST(SpawnAsync, exit_code) {
 
   EXPECT_EQ(WEXITSTATUS(status), 42);
 }
+
+TEST(SpawnAsync, env) {
+  pid_t pid = spawn_async([] { exec_sh("exit $EXIT", {{"EXIT", "45"}}); });
+  int status = 0;
+  pid_t res = waitpid(pid, &status, 0);
+
+  EXPECT_EQ(res, pid);
+
+  EXPECT_EQ(WEXITSTATUS(status), 45);
+}