DATA_DIR override with environment variable (#333)

src/common.hpp

@@ -0,0 +1,20 @@
+// SPDX-License-Identifier: Apache-2.0
+/*
+ * Copyright (C) 2023 Gwenhael Goavec-Merou <[email protected]>
+ */
+
+#ifndef SRC_COMMON_HPP_
+#define SRC_COMMON_HPP_
+
+#include <string>
+
+/*!
+ * \brief return shell environment variable value
+ * \param[in] key: variable name
+ * \param[in] def_val: value to return when not found
+ * \return variable value or def_val
+ */
+const std::string get_shell_env_var(const char* key,
+	const char *def_val="") noexcept;
+
+#endif  // SRC_COMMON_HPP_